Infertility Caused by Abnormalities of the Female Tubular Genitalia

Change

Foaling Rate (%)

PERSISTENT UTERINE INFECTION. Treatment of mares with persistent uterine infections needs to be directed toward the underlying breakdown of the uterine defense and against the microbial agent. The first therapeutic concern should be to remove predisposing causes, such as a breakdown of external genital barriers. Persistent uterine infection frequently follows degenerative or traumatic anatomic changes and loss of integrity of the barriers of ascending infection. Therefore Caslick's surgery, repair of cervical damage and perineal lacerations, and correction of urovagina should precede specific endometrial treatment. All potential sources of contamination, including intrauterine passage of diagnostic and treatment implements, should be minimized. In some mares, recovery follows with sexual rest and no further treatment. Mares that are susceptible to persistent uterine infections should be bred using minimal contamination techniques to avoid bacterial contamination of the uterus.⁷⁴ Antibiotics may be administered by either local or systemic routes. Intraluminal fluid and inflammatory debris should be removed by uterine lavage before local treatment. Drugs and doses are summarized in Table 43.6. Treatment should be based on sensitivity. Mares should be treated during estrus when natural defense is maximal, and strict aseptic technique should be used. The volume of fluid used for antibiotic therapy depends on the size of the uterus. A total volume of 30 to 60 mL is usually sufficient. Treatment should continue daily for 4 to 6 days during the duration of estrus. Repeated contamination may indicate an unsuccessfully resolved predisposing cause. The clitoral fossa should always be con­sidered as a primary location of bacteria grown in these cases. If culture results from the endometrium and clitoral fossa match, the clitoral fossa should be cleaned and treated locally with antibiotics. Removal of the primary microorganism may result in overgrowth of a second bacteria or fungus (superinfec­tion). Critical studies of the efficacy of systemic antibiotics are limited, although effective concentration of amikacin has been measured in the endometrium after systemic administration.⁷⁵ Parenteral administration may be easier, and the opportunity to introduce uterine contamination or cause uterine irritation with treatment is eliminated. Treatment of fungal infections is generally more challenging than treatment of bacterial infections. Culture and sensitivity will determine the choice of antifungal drugs (see Table 43.6). Fungal endometritis may require daily intrauterine infusions for 7 to 10 days to effectively resolve the infection. To avoid intrauterine infusions in the presence of high circulating concentrations of progesterone, treatment can be initiated 1 or 2 days after an injection of PGF2α in diestrual mares and continued until 1 or 2 days after ovulation. A single dose of a benzoylphenyl urea (lufenu- ron) has been suggested to effectively treat mares with fungal endometritis.⁷⁶

Antimicrobial Alternatives and Supplemental Treat­ments. Although suitable antibiotics are the most effective treatment against infectious endometritis, recent research has focused on situations where this treatment alone is not sufficient to eliminate bacterial growth from the uterus. Suggested pres­ence of biofilms, dormant bacteria in the deeper layers of the endometrium, and other barriers may prevent antibiotics from reaching their target and effectively eliminating bacteria.^77-79 Although further evidence may be needed to conclusively confirm some of these hypotheses, their suggestive presence in the uterus have given rise to multiple treatment options to accompany or replace traditional antibiotics. The medical value of most of these treatments is often anecdotal rather than evidence based.

■ TABLE 43.6

Antibacterial Drugs Used for Intrauterine Administration for Treatment of Uterine Infections in Mares

N-acetylcysteine (NAC): This mucolytic substance has been used to reduce the viscosity of mucus in the uterus. In addition, NAC has been suggested to have antiinflammatory, antioxi­dant, and antibacterial activity.⁸⁰ Typically, 30 mL of a 20% solution NAC (200 mg/mL) is diluted in 150 mL of saline and infused into the uterine lumen during estrus, followed by ecbolic treatment or uterine lavage 12 hours after treatment. The treatment protocol has been suggested to be beneficial both 24 to 48 hours prior to breeding and 24 hours prior to antibiotic treatment. Repeated lavage may be indicated if the effluent fluid is cloudy.⁸¹ When used together with antibiotics, the interaction with antimicrobials should be kept in mind. NAC enhances the efficacy of β-lactams but reduces the antibacterial activity of aminoglycosides, fluoroquinolones, and erythromycin. Oral treatment with NAC at 10 mg/ kg did not reduce viscosity of uterine mucus; however, an antiinflammatory effect was observed in one study.⁸² NAC was also suggested to decrease biofilm biomass and reduce bacteria within biofilms of E. coli isolates in vitro.⁷⁹ The same effect, however, was not observed for other bacteria. Intrauterine treatment with NAC is sufficiently proven to be safe and has been suggested to improve pregnancy rates, although the pregnancy data were not supported by 77

controlled experimental conditions.⁷⁷

EDTA-Tris: Tricide® (a third-generation chelator) chelates calcium and magnesium within the bacterial cell wall, which may potentiate the effect of the antibiotic.⁸³ It has been suggested to potentiate the effect of antibiotics on some bacteria, but its effect to disrupt gram-negative biofilms is less clear.⁷⁹ Treatment protocols often consist of intrauterine infusions of 250 to 750 mL Tricide followed by uterine lavage with a buffered saline solution the next day. The treatment is repeated until the effluent fluid is clear, at which time the mare is treated with local antibiotics for 5 days. Tricide can also be added to antibiotics but is not recommended for use together with ceftiofur, penicillin K, or Timentin due to precipitation in the solution.⁸¹

Cationic steroid antimicrobial (CSA): Ceragyn® belongs to a class of peptides that cause depolarization of bacterial cell wall membranes and activate apoptotic pathways. These peptides have been used for various conditions in human medicine because of their biofilm breakdown and broad­spectrum antimicrobial activities. Ceragyn (60 mL; 1 vial) is labeled for use up to 24 hours before or 12 to 48 hours after breeding. The drug has become increasingly popular among equine practitioners, but the authors have not been able to find conclusive data from controlled studies to support its effect on equine endometritis.

Hydrogen peroxide: H₂O₂ has a bactericidal effect on most uterine pathogens. A 1% solution (20 mL of a 3% H₂O₂ solution diluted in 60 mL lactated Ringer's solution [LRS]) has been suggested to be effective on biofilms in vitro.⁷⁹ Information regarding the efficacy of H₂O₂ treatment is anecdotal and needs to be supported by controlled in vivo studies.

bActivate: A proprietary substance marketed as bActivate® has been shown to activate dormant Streptococcus spp. from the equine endometrium.⁷⁸ Dormant bacteria are not sensitive to antibiotics, but after confirmed activation with bActivate, evidenced by a positive culture, mares can successfully be treated with intrauterine infusion of antibiotics. However, fertility data from controlled studies are needed to confirm claims of improved fertility following treatment.

Immune Modulators. The immune response of the equine endometrium has been investigated following bacterial inoculation, and treatment protocols aimed at restoring a normal immune response in susceptible mares have been reported.⁸⁴ Bacterial cell wall extracts: Cell wall extracts of Mycobacterium phlei (MCWE) as well as Propionibacterium acnes have been investigated regarding their effect on the uterine immune system and reproductive performance. Fumoso and col- leagues⁸⁵ found that MCWE treatment of susceptible mares at the time of breeding resulted in an endometrial immune environment similar to that of resistant mares at 24 hours after AI. In a follow-up study,⁸⁶ the authors concluded that MCWE treatment was effective in eliminating inoculated bacteria from the uterus in 70% of treated mares at 7 days after infusion. In another study,⁸⁴ the immune response between 3 and 72 hours after intrauterine inoculation of E. coli was characterized; cytokine expression in MCWE- treated mares was not different from that of untreated mares, but messenger RNA (mRNA) expression of serum amyloid A was suppressed in treated mares. Clinically, MCWE had a favorable effect on the clearance of pathogens and fluid retention.⁸⁴ These results supported a comprehensive clinical study in which problem mares were treated with P. acnes extract (Settle®); the authors found a 10% increase in pregnancy rates compared to untreated controls.⁸⁷ However, the mares received additional treatments and the effect of stallion fertility was not considered in that study.

Plasma: Intrauterine infusion of autologous or heterologous plasma has been used to treat mares with infectious endo­metritis.⁸⁸ The rationale for the treatment was to add immunoglobulins and complement to assist the mares in eliminating pathogens from the uterus. Supplementation of fresh or cryopreserved PMNs into the uterine lumen in mares with persistent endometritis has also been proposed 8991

as an alternative treatment to antibiotics.^89-91

PERSISTENT BREEDING-INDUCED ENDOMETRITIS. Manage­ment of mares susceptible to persistent breeding-induced endometritis should include limiting uterine exposure to semen and bacteria and assisting the uterus to physically clear con­taminants and inflammatory products after breeding.^30,92 Preexisting uterine infections should be resolved before the mare is bred. Exposure to semen should be limited to a single breeding per cycle, if possible. This can be accomplished by closely monitoring follicular development and hormonal treatment to induce ovulation of mature follicles.

Woodward and colleagues³⁷ found that the imbalance of proinflammatory cytokines and inflammatory cytokines in response to semen in susceptible mares is present already within 3 to 6 hours after insemination. This information should serve as a guideline for timing of treatments in susceptible mares after insemination.

Uterine lavage: Infusion of 1 to 2 L of buffered saline solution after breeding is effective in removing accumulated fluid and inflammatory products from the uterus. Because sperm transport to the oviduct is completed within 4 hours after breeding, uterine lavage 6 to 24 hours after breeding will not have a negative effect on fertility.⁵³ The uterine lavage is typically repeated until the recovered effluent fluid is clear. The treatment is often combined with an ecbolic drug in order to facilitate recovery of the infused fluid.^81,90,92

Manual dilation of the cervix in mares with poor cervical dilation may help these mares more effectively clear the uterus of fluid.

Ecbolics. The administration of ecbolic drugs after breed­ing is effective in overcoming impaired myometrial contractility 9395 in susceptible mares.^{93 95}

Oxytocin: Low doses of oxytocin appear to be more effective than high doses.⁹⁶ A common treatment protocol is 10 to 20 IU of oxytocin 4 to 6 hours after breeding, repeated every 6 to 8 hours until the intraluminal fluid has disap­peared. The half-life of oxytocin is relatively short, resulting in approximately 50 minutes of myoelectric activity after the administration of 10 IU.⁹⁷

Carbetocin: Carbetocin is a long-acting oxytocin analog with an extended half-life after administration of 0.175 mg IV.⁹⁸ Limited data are available on the efficacy of carbetocin versus oxytocin.

Prostaglandin: PGF2_α has considerably longer duration on uterine contractility compared to oxytocin.⁹⁵ Treatment is not recommended after ovulation, since PGF2_α and its analogs can cause a delay in the formation of a functional CL when administered within 2 days after ovulation.^36-39 It is the authors' observation that luteolytic doses of PGF_2α are excessive and may cause myometrial “cramp” initially rather than a physiologic contraction that would be more suitable for removing fluid from the uterus. A suitable dose of PGF_2α and its analogs for treatment of equine endometritis has not been established. In severe cases of persistent breeding- induced endometritis, ecbolic treatment is often combined with uterine lavage with 1 to 2 L of buffered saline 6 to 12 hours after breeding.⁸¹

Social interaction with a stallion: Social interaction with a stallion may facilitate normal uterine clearance following breeding. Audio, visual, and physical exposure of mares to a stallion stimulated pituitary oxytocin release and caused uterine contractions.¹⁰⁰ This observation was confirmed in a sub­sequent report.¹⁰¹ Housing susceptible mares close to a tease stallion after breeding may therefore enhance normal uterine activity and clearance.

Immune Modulators. The immune response of the equine endometrium has been investigated following insemina- tion,³⁷ and treatment protocols aimed at restoring a normal immune response in susceptible mares after breeding have been reported.

Corticosteroids: Several studies support a positive clinical effect of corticosteroids on persistent breeding-induced endometritis. A single dose of dexamethasone (50 mg at the time of breed­ing) was found to improve pregnancy rates in mares with more than three risk factors for susceptibility to persistent breeding-induced endometritis.¹⁰² Researchers from Belgium did not observe a positive effect of treatment with 10 mg or 20 mg of dexamethasone 6 to 12 hours after AI in a large group of unclassified mares,¹⁰³ emphasizing the importance of correctly identifying mares as susceptible to persistent endometritis before implementing treatment regimens. Furthermore, mares with a history of excessive postbreeding inflammation had significantly higher pregnancy rates when treated with acetate 9-α-prednisolone (0.1 mg/kg) twice daily compared to control cycles.¹⁰⁴

Although the immune modulation appears to favor resolution of inflammation, it does not mimic that of resistant mares.¹⁰⁵ Recent observations suggest that dexamethasone suppresses the proinflammatory cytokine interleukin-1β (IL-1β) in susceptible mares at 6 hours after breeding.¹⁰⁶ However, no effect was observed for modulating cytokines, which previously had been suggested to differ between susceptible 37

and resistant mares.³⁷

Nonsteroid antiinflammatory drugs (NSAIDs): Because of its modulating effect on inflammation, treatment of susceptible mares with NSAIDs has been studied.¹⁰⁷ Oral administration of Vedaprofen (2 mg/kg) the day before AI, and of 1 mg/ kg twice daily until one day after ovulation, had no effect on fluid accumulation or uterine cytology but resulted in higher pregnancy rates. It should be noted that the mares were also treated with oxytocin (20 IU) three times per day. More research is needed to determine the potential value of this treatment protocol.

Bacterial cell wall extracts: Studying the immune response to semen, Woodward and colleagues¹⁰⁵ found that MCWE downregulated mRNA expression of IL-1β in susceptible mares at 6 hours after AI, supporting previous observations by Fumuso and colleagues.¹⁰⁸ As noted under infectious endometritis, a comprehensive clinical study suggested that treatment of problem mares with P. acnes extract (Settle®) resulted in a 10% increase in pregnancy rates compared to untreated controls.⁸⁷ However, the mares received additional treatments and the effect of stallion fertility was not con­sidered in that study.

Plasma: The use of plasma products has recently been directed toward immunomodulation rather than elimination of pathogens from the uterus. Platelet-rich plasma (PRP) was shown to modulate the uterine inflammatory response to semen,^109,110 including downregulation of mRNA coding for proinflammatory cytokines and NO.¹¹¹ The protocol for treatment with PRP entails separation of 180 mL of whole blood by a special centrifugation system (Angel Cytomedix, Inc., Gaithersburg, Md.) followed by resuspension of the PRP in 10 mL plasma before the mix is being infused into the uterus at 24 to 36 hours prior to breeding.

Lactoferrin: Recombinant human lactoferrin (rhLF) has been demonstrated to be safe to administer in the equine uterus and modulates breeding-induced inflammation.¹¹² It was concluded that intrauterine treatment with 250 μg/mL rhLF may assist susceptible mares to resolve the breeding-induced inflammation in a timely fashion. Clinical trials are needed to confirm this observation.

Electroacupuncture has been used clinically to increase uterine contractility in mares with delayed uterine clearance. Anecdotal reports are encouraging, and further research is necessary.

It is important for the clinician to keep in mind that a tran­sient inflammatory response to semen is normal. Postbreeding treatment of these mares most likely will not improve fertility but may cause even further contamination and interfere with pregnancy. Only 10% to 25% of all broodmares develop a patho­logic, persistent form of breeding-induced endometritis.^19-21 Attention should be given to identifying and managing these mares appropriately in order to optimize reproductive efficiency.

CHRONIC DEGENERATIVE ENDOMETRITIS (ENDOMETRIO­SIS). Degenerative changes of the endometrium such as periglandular fibrosis and glandular dilation are often seen in older multiparous mares. The condition is associated with susceptibility to persistent endometritis⁶⁸ and may result from repeated uterine inflammation. However, the condition has also been observed in older mares without any known history of endometritis, suggesting that degenerative fibrosis of the endometrium can be a process of aging rather than inflam- mation.¹¹³ Because of the possibility of a noninfectious cause of the disease, it was suggested that the condition should be called endometriosis, rather than degenerative endometritis.¹¹³ It is not clear why mares with fibrotic degenerative changes to the endometrium have an impaired physical uterine clearance mechanism. Sclerotic changes in the uterine vascular bed impair blood flow to both the endometrium and the myometrium, which may explain the effect on uterine clearance.¹¹⁴

Several treatments have been suggested for degenerative fibrosis of the endometrium, but consistent results have not been reported. Infusion of dimethyl sulfoxide (DMSO) into the uterine lumen has produced inconsistent results in mares with chronic degenerative endometritis.^115,116

The use of mesenchymal autologous stem cells and autolo­gous conditioned serum has been explored in experimental models as potential treatment alternatives for susceptible mares and mares with degenerative endometrosis.^117-119 A modulation of the inflammatory response to semen was reported as was an indication that regenerative treatment strategies have the potential to restore degenerative changes to the endometrium.

Prognosis and Prevention. Prognosis for fertility after endometritis varies with the severity of inflammation and fibrosis and the inciting cause. Prognosis should take into account the age of the mare, the level of reproductive management, the cause (if known), and the most probable response to treatment.

Metritis

Metritis is classically defined as inflammation of all layers of the uterine wall. Metritis occurs in the first 2 weeks after foaling and commonly follows abortion, dystocia, and RFMs. Equine metritis is often accompanied by endotoxemia and laminitis. Transluminal adhesions between endometrial folds may follow severe metritis.

■ Clinical Signs and Diagnosis Metritis is characterized by uterine accumulation of postpartum secretions, bacteria, and the products of inflammation, with discharge from the cervix and possibly the vulva. Discharge is usually fluid and red-brown and may be fetid. Systemic signs of depression accompanied by neutropenia and leukopenia are apparent with development of endotoxemia. Differential diagnoses include normal lochia and causes of profound depression in the postpartum period as a result of uterine tears and acute abdominal disorders.

■ Treatment and Prognosis Treatment is directed toward removing contamination and microorganisms from the uterus while providing systemic treatment for endotoxemia. Broad-spectrum systemic antibiotics, antiinflammatory drugs, and fluid therapy are indicated. Uterine contamination may be removed by gentle intraluminal infusion of warm water or saline and siphoning off of uterine contents. Vigorous lavage should be avoided, particularly during acute systemic disease. Prognosis depends on severity of clinical signs. If metritis is diagnosed quickly and treatment is instituted, prognosis for fertility and systemic health is good. Prognosis is guarded once endotoxemia and laminitis develop.

Pyometra

Pyometra in mares is an accumulation of purulent exudate in the lumen of the uterus. Impedance to mechanical uterine outflow, such as cervical fibrosis and adhesions of cranial parts of the tract ventrally into the abdomen, often contributes to the development of pyometra. If endometrial irritation causes release of endogenous endometrial PGF_2α, diestrus will be shortened. In some mares, endometrial destruction is so severe that PGF_2α release is inadequate and luteal life is prolonged.²⁷ A variety of bacteria may be involved, including E. coli, Pseudomonas spp., and Streptococcus spp. Cultures may also be negative.

■ Clinical Signs and Diagnosis A purulent vaginal or cervical discharge may be seen. The mare may demonstrate a short diestrus, a normal interestrous interval, or a prolonged diestrus. Some mares with pyometra have mild leukopenia and normocytic-normochromic anemia, secondary to mild sup­pression of erythropoiesis. Transrectal palpation and ultraso­nography reveal a fluid-filled uterus. The uterine wall may be thin and flaccid or thick.

■ Treatment and Prognosis Treatment should involve correction of predisposing causes, fluid evacuation, and local antibiotic treatment. Evacuation of large amounts of fluid from the uterus may result in redistribution of fluid and circulatory shock. The mare should be monitored for signs of circulatory shock, and intravenous fluid may be administered during evacuation of large amounts of fluid from the uterus. The prognosis for life is excellent; however, the prognosis for return to normal fertility is guarded to poor because the conditions that predispose to development of pyometra in mares (cervical stenosis and adhesions) are difficult to treat and because severe endometrial destruction may develop. Endometrial biopsy should precede vigorous treatment. Hysterectomy should be considered if treatment is unsuccessful and if discharge is unacceptable or if adhesions impair athletic ability.

■ Ruminants

Bovine Uterine Infection

Deliveries complicated by dystocia or RFMs may be followed by severe bacterial infections of the uterus. The most sanitary environment possible should be provided for calving. The use of a clean pasture may be most appropriate on some farms, whereas the use of roomy, well-bedded, indoor maternity pens that are cleaned after each delivery may be appropriate on others.

Cows with abnormalities such as hypocalcemia, dystocia, and RFMs around the time of calving are more likely to develop uterine infections than are cows that calve normally. Routine treatment of cows with antibacterial drugs and chemicals has not been shown to be beneficial and may in fact reduce fertility. Postpartum uterine infections may be prevented, or the number of such infections reduced, by strict attention to sanitation in the calving environment and during assistance with delivery, along with proper management during the dry period.¹

Bovine uteri are normally contaminated by a wide variety of microorganisms during the puerperium. Most of the organ­isms are transient residents of the reproductive tract and are soon eliminated from the involuting uteri of normal cows. T. pyogenes can persist in the uteri of cows and act with Fusobac- terium necrophorum and Prevotella (formerly Bacteroides) spp. to cause uterine infections. Coliforms, P aeruginosa, hemolytic streptococci, and gram-positive and gram-negative anaerobic bacteria are also frequently isolated from animals with post­partum uterine disease. T. pyogenes and Clostridium spp. occasion­ally colonize the postpartum uterus synergistically, causing severe gangrenous metritis. Other organisms that appear to have little effect on fertility may colonize the uterus and produce penicillinase, thus influencing the selection and route of administration of drugs used to treat uterine infections.^2,3

■ Clinical Signs and Diagnosis Lochia is normally expelled during the first 2 weeks after calving and may range from dark red or brown to white to clear. If uterine involution is delayed, discharge of lochia may continue until 30 days after calving. Discharge of lochia is not abnormal unless the fluid is fetid or the cow develops other abnormal clinical signs. Abnormalities of uterine involution cannot be diagnosed by palpation per rectum during the first several days after calving when both normal and abnormal uteri are out of reach and cannot be safely retracted. By 10 to 15 days after calving, the entire uterus can be palpated if involution is normal. Fluid should not be palpable within the uterine lumen by 14 to 18 days after calving. Gross reduction in size and histologic repair of the endometrium are complete in dairy cows by 40 to 50 days after calving.

Postpartum metritis in cows is characterized by the presence of variable amounts of lochia within the uterine lumen that may be discerned by palpation per rectum. A vaginal discharge is usually present, but it may become obvious during palpation. Septic or puerperal metritis is characterized by clinical signs of toxemia that may include fever, depression, partial or complete anorexia, and laminitis. Milk yield is depressed, and cows may be unwilling or unable to rise. Some cases may be complicated by tenesmus. Vaginitis and cervicitis may accom­pany metritis. Discharges associated with septic metritis vary from scanty white mucus to copious amounts of red to red-black, watery, malodorous fluid. In some cases inflammation may spread through the uterine wall and cause perimetritis and peritonitis.⁴ Septic metritis in ewes and does is characterized by fever, depression, anorexia, and tenesmus.

Endometritis in cattle is usually observed between 2 and 8 weeks after calving. Discharge can range from white pus to estrual mucus. Purulent exudate may be observed only with palpation or may be found in the cranial vagina and cervical canal on examination with a speculum. The history may indicate that the cow has failed to conceive after several services but the patient is otherwise healthy.

Culture of endometrial fluid is not usually done in individual cases of bovine uterine infection but may be indicated to determine the antibiotic susceptibility of microorganisms on a particular farm or as a part of the diagnostic plan when the incidence of postpartum metritis or endometritis increases suddenly.

Endometrial biopsies are rarely used in cows but have been recommended when complete evaluation is required of the reproductive tracts of cows that do not conceive or that conceive but do not complete their pregnancies.

■ Treatment and Prognosis To be useful in treating uterine infections in cows, an antibiotic must be active against the primary uterine pathogens (T. pyogenes and gram-negative anaerobes), in the presence of organic debris, and in the anaerobic environment of the postpartum bovine uterus.⁵ Oxytetracycline is active against many of the microorganisms that infect the bovine uterus, and its activity is only slightly reduced by organic debris and absence of oxygen. Intrauterine treatment with administration of 4 to 6 g of oxytetracycline per day has been used; however, some preparations of oxytet­racycline irritate the endometrium, cervix, and vagina. Intrauterine antibiotic treatment of dairy cows results in residues in their milk.⁶ For example, oxytetracycline has been found in milk from 447 to 96⁸ hours after intrauterine administration, and thus an appropriate withdrawal period should be enforced and milk residue testing should be conducted.

Penicillin by systemic administration is effective for treatment of uterine infections in cows. Doses of penicillin required to reach the minimum inhibitory concentration of T.pyogenes are 10,000 to 20,000 IU/kg/day. Systemic ceftiofur (2.2 mg/kg IM or SC q24h for 3 to 5 days) achieves adequate concentrations in the uterus and is effective in treating bovine metritis.^9,10

Treatment of septic or puerperal metritis should be directed toward controlling septicemia. Large doses of broad-spectrum systemic antibiotics are indicated, along with fluids and other supportive therapy. Attempts to remove RFMs or irrigate the uterus are contraindicated during the acute phase of the disease. After the patient has recovered from acute septicemia, intra­uterine therapy may be considered.

ANTISEPTIC CHEMICALS. A variety of antiseptic chemicals have been infused into the uterine lumen of cows in attempts to treat metritis and endometritis, but few controlled trial evaluations are available. The potential for endometrial damage by these chemicals needs to be considered carefully.

UTERINE LAVAGE. Lavage of the uterine lumen with large volumes of warm saline (40° to 45° C [104° to 118° F]) removes accumulated fluid and debris. Uterine lavage has been used as an adjunct to antibiotic, antiseptic, and plasma treatment. Catheters designed for nonsurgical embryo recovery are suitable for uterine lavage. Saline is infused into the endometrial cavity in 0.5- to 1-L increments, allowed to reflux through the catheter, and collected for inspection. A milk hose and larger fluid volumes may be used in cattle with larger postpartum uteri, but care must be taken not to enter far into the uterus because it is friable and easily perforated. Massage or partial retraction of the uterus by palpation per rectum may be necessary to increase fluid recovery. The uterine lumen is lavaged repeatedly until the fluid returning through the catheter is no longer turbid.

PROSTAGLANDINS. In cows, repeated administration of PGF_2α results in shortened estrous cycles and may mimic the shortened luteal phase of patients with acute endometritis. PGF_2α therapy alone may be sufficient in mild cases of endo­metritis, or it may be used in combination with intrauterine or systemic therapy. In cases of chronic bovine endometritis, treatment with PGF_2α one or two times at 10- to 14-day intervals decreased the number of days open.¹¹

The prognosis in cows for recovery from endometritis is usually good if the condition does not progress to a more severe form of uterine disease. Septic metritis after dystocia or RFMs may result in permanent impairment of reproductive function, laminitis, or death of the patient despite aggressive therapy.

Pyometra

In dairy cows, pyometra is likely to develop in cows that ovulate before microorganisms that infect the uterus during the post­partum period are eliminated. The CL that develops after the first postpartum ovulation at approximately 15 to 18 days after calving persists, possibly because the abnormal uterine contents suspend release of PGF_2α from the endometrium or sequester it within the uterine lumen. The uterus is brought under the influence of progesterone, which depresses phagocytic activity of uterine neutrophils and closes the cervix, allowing the bacterial infection to persist.¹² Pyometra rarely endangers the general health or life of affected cows. Postcoital pyometra may be caused by T. foetus in natural breeding dairy and beef herds.¹³

PGF_2α is the treatment of choice for bovine pyometra. Treatment is followed in 3 to 6 days by uterine evacuation in 85% to 90% of treated cows. Response to PGF_2α treatment may be bolstered with a repeat injection in 6 to 12 hours. After endometrial lesions are allowed to heal for 30 days, fertility is restored in most patients.

Treatment of cows with GnRH after calving is controversial. In herds with a high prevalence of postpartum uterine infections, treatment with GnRH may decrease fertility by inducing ovulation and CL development; thus the uterus is brought under the influence of progesterone before contaminating bacteria are removed, leading to pyometra.

Perimetritis

Perimetritis may occur in all species as a sequela to severe uterine infections, uterine rupture, penetration of the vagina during mating, traumatic insemination or obstetric procedures, and cesarean section.¹⁴ Perimetritis is characterized by inflam­mation of the peritoneal surface of the uterus and may be accompanied by localized or diffuse peritonitis. Adhesions then develop between the uterus and other pelvic and abdominal organs.

■ Clinical Signs and Diagnosis The clinical signs of perimetritis are those of peritonitis and may include fever, depres­sion, partial or complete anorexia, stasis of the gastrointestinal tract, and evidence of abdominal pain. Abdominal pain is typified by colic in mares and by grinding the teeth (odontoprisis) in cows. In cows the condition should be differentiated from traumatic reticuloperitonitis, displacements of parts of the digestive tract, abomasal ulcers, postpartum metritis, and abdominal fat necrosis. Perimetritis in mares must be differentiated from other causes of colic. Antemortem diagnosis of perimetritis is difficult in sheep and goats that are presented mainly with fever, depression, anorexia, and odontoprisis.

■ Clinical Pathology Cases of acute perimetritis are accompanied by leukopenia, neutropenia, and a degenerative left shift. Further evidence of peritonitis is obtained when peritoneal fluid is obtained by paracentesis and examined for its cellular and microbiologic content.

■ Treatment and Prognosis The cause of perimetritis should be treated if possible. Cases of severe metritis should be treated appropriately, and uterine ruptures sutured if possible. Repair of uterine ruptures inaccessible by flank incisions may be facilitated by intentional prolapse of the uterus after administration of epinephrine, provided the tear is not too close to the cervix (see next section). Treatment with broad­spectrum systemic antibiotics is indicated. Lavage to remove peritoneal exudate has been recommended but is difficult to accomplish, especially in cows in which the rumen, abomasum, and greater omentum make ventral drainage almost impossible and in which fibrinous peritonitis with loculation of infection occurs rapidly. Other supportive treatments such as intravenous fluids and antiinflammatory drugs should be administered.

The prognosis depends on the severity of lesions. Fatalities can occur despite prompt treatment, and surviving animals may be infertile because of mechanical interference with gamete transport caused by adhesions between the genital organs and other pelvic and abdominal tissues. In general, the prognosis for fertility in affected animals is fair at best.

■ Prevention and Control Perimetritis occurs sporadically in individual animals; therefore prevention depends on avoiding the causes. Immature females, especially heifers and fillies, should not be allowed at pasture with adult males to prevent undesired mating complicated by penetration of the vagina. Traumatic obstetric, insemination, and uterine lavage procedures must be avoided. Uterine tears that occur at parturition must be sutured immediately. Postpartum metritis must be treated promptly and appropriately before it progresses to perimetritis.

■ Small Ruminants Uterine infections may follow dystocia and RFMs in sheep and goats, but these infections are not frequently a cause of infertility because in most cases parturition is followed by a few months of sexual rest before the next breeding season. In ewes, RFMs and metritis follow abortion caused by Listeria monocytogenes, Campylobacter spp., and Chlamydophila abortus.

Ewes and does affected with metritis are usually treated with systemic antibiotics such as penicillin, sulfamethazine, oxytetracycline, or ceftiofur. Early and aggressive treatment is indicated.

■ Camelids

Metritis and Endometritis

When camelids breed, the penis is inserted through the cervix and deep into the uterine horns. Unnecessary mating, or overbreeding, is the most important factor causing damage to and contamination of the uterus.¹⁵ Other major contributing factors include RFMs, rectal vaginal tears, and unsanitary obstetric manipulations.¹⁵

Chronic endometritis will often not cause evident clinical signs, whereas acute, postpartum endometritis may cause fever, depression, and signs of shock. A thick, mucoid lochial discharge is normal in the postpartum female for up to a week postpartum. In contrast, thin, watery, fetid discharge is a sign of endometritis.¹⁵

Transrectal ultrasonography and vaginoscopy are helpful in diagnosing endometritis and metritis. Inflamed, thickened uterine walls and hyperechoic, intraluminal fluid may be present on ultrasound examination. Vaginoscopy may reveal cervical discharge. Transrectal ultrasonography may usually be per­formed in llamas. In alpacas, because of smaller size, an extension probe is necessary to facilitate transrectal ultrasonographic evaluation.

Uterine culture and cytology samples from the llama may be obtained using methods similar to those used in the mare and cow. A double-guarded swab prevents environmental contamination. In the alpaca, the swab should be passed through the cervix via visualization using a vaginoscope. These diag­nostics should be performed during the peak follicular phase to ensure ease of passage through the open cervix and more reliable test results.¹⁵ The most common bacteria isolated from the uteri of camelids with endometritis are E. coli, S. zooepi- demicus, β-hemolytic streptococci, Enterococcus, coagulase­negative Staphylococcus, Proteus spp., Enterobacter aerogenes, K. pneumoniae, and T. pyogenes.¹⁵

Uterine biopsy can be a useful diagnostic tool for evaluation of metritis and endometritis in camelids. Endometrial biopsy samples in llamas may be obtained as in the mare. The left horn is perhaps better to target unless a particular pathology is suspected in the right horn, because camelid pregnancies almost always occur in the left horn.¹⁵ Pathologic changes, evaluation, and prognosis are all assumed to be similar to those in the mare.

Treatment for endometritis and metritis is also similar to that described for the mare. Uterine lavage with a warm, isotonic saline solution and oxytocin injection (5 to 10 IU) are the major components of treatment. Intrauterine antibiotic infusion is done after uterine lavage. The most common antibiotics used are penicillin K (1.5 ? 10⁶ U), gentamicin sulfate (200 to 300 mg), and ceftiofur sodium (250 to 500 mg).¹⁵ Antibiotics should be diluted in sterile water or saline (saline should not be used with ceftiofur) and given once daily for 5 to 7 days. Females should be evaluated after cessation of treatment and completion of 2 weeks of sexual rest.

Prevention of endometritis often requires a “minimum contamination breeding technique.”¹⁵ This entails monitoring follicular growth via transrectal ultrasound until the follicle is of preovulatory size, breeding only once, following breeding with an injection of hCG (750 IU) or GnRH, and administering an intrauterine infusion of antibiotics 24 hours after breeding. Females should be evaluated for pregnancy 12 to 14 days after breeding.

Further preventative measures include performing prebreed­ing examinations on all maiden animals to avoid breeding animals that are too young or do not have follicular activity; breeding only females that exhibit strong receptive behavior (as opposed to mere submissive behavior); performing complete gynecologic examinations on all females with a history of infertility, obstetric problems, or postpartum complications; and observing strict rules of hygiene during breeding and obstetric manipulations.¹⁵

Pyometra

Pyometra caused by delayed uterine involution may be observed shortly after parturition. Chronic pyometra is often associated with vaginal or cervical adhesions that may be sequelae to trauma after dystocia or aggressive obstetric manipulation.¹⁵

Anatomic Defects as a Cause of Uterine Infection

The most common anatomic defect associated with genital infections in camelids is pneumovagina. Other defects include urovagina and perineal lacerations. These defects should be corrected to prevent contamination with environmental and fecal organisms.

Endometrial Cysts and Lacunae

■ Mares Endometrial cysts and lymphatic lacunae are common degenerative changes of the endometrium that are more prevalent in mares older than 11 years of age than in younger mares.¹⁶ Endometrial cysts can originate from endo­metrial glands or obstructed lymphatics. Glandular cysts are small (and Prognosis The prolapsed uterus should be washed with clean saline and replaced manually in the standing mare as rapidly as possible. Replacement is aided by sedating the mare and administering epidural anesthesia. The uterus should be supported on a clean sheet held at the level of the pelvis. The uterus should be replaced, beginning with the uterine body and working gradually, replacing the tip of the horns last. Correct positioning of the uterus is important to prevent the prolapse from recurring. Replacement should be followed by treatment with broad-spectrum antibiotics, antiinflammatory drugs, and intravenous isotonic fluids. Treat­ment with oxytocin (10 to 20 IU IM) facilitates uterine involu­tion. Prognosis is related to development of sequelae such as uterine tears, metritis, and endometrial damage.¹⁸

■ Ruminants In cows, most cases of uterine prolapse occur within a few hours after calving. The condition is invariably associated with hypocalcemia, which results in lack of uterine tone and delayed cervical involution. In addition, dystocia frequently precedes uterine prolapse.

Elective uterine prolapse can be induced within 6 to 12 hours after calving by administering epinephrine to relax the uterus for the repair of uterine tears. A 10-mL amount of epinephrine (1:1000) is diluted to 250 mL in sterile saline and administered slowly IV. After 100 mL of the solution has been given, the operator reaches through the cervix, grasps the uterine wall and caruncles, and everts the uterine horn toward the cervix. When sufficient uterine tissue has entered the cervical canal, the patient responds by straining, which assists in completion of the prolapse. Epidural anesthesia is administered to abolish further straining after the prolapse is complete.

Uterine prolapse in does has been associated with dystocia, hypocalcemia, and lack of exercise. The predisposing factors are probably similar for ewes.

■ Clinical Signs and Diagnosis Clinical signs of uterine prolapse are obvious, with maternal caruncles exposed on the uterine endometrium. The membranes may remain attached. Immediately after prolapse occurs the tissues are nearly normal, but within a few hours they become enlarged and edematous. The endometrium is usually contaminated with feces and bedding material. In some cases the prolapsed tissue may be lacerated or severely traumatized and may contain loops of intestines.

Clinical signs that may accompany uterine prolapse include straining, abdominal pain, restlessness, anorexia, and increased pulse and respiratory rates. Parturient paresis is common in affected dairy cows. In most patients these signs are transitory, but shock may complicate some cases.

■ Clinical Pathology Uterine prolapse in cows is frequently accompanied by hypocalcemia and a significant increase in the packed cell volume.¹⁹

■ Treatment and Prognosis The prolapsed tissue should be protected from further damage by wrapping it in wet towels or covering it with a plastic bag. Beef cows should be restrained where they are found, to prevent trauma to the uterus or rupture of the large uterine vessels should an animal try to escape on arrival of the clinician. Treatment of hypocalcemia is usually indicated before replacement of the uterus if the cow is recumbent and semicomatose; otherwise calcium glu­conate is administered after replacement. Epidural anesthesia (3 to 5 cc of 2% lidocaine) is frequently, but not always, required.

The prolapsed tissue is washed with a mild presurgical scrub. The membranes are removed if they can be easily separated from the endometrium but are left in place if removal is difficult. Some clinicians recommend that cows stand during replacement, whereas others have found that the organ can be replaced in recumbent cows if the patient is placed on her sternum with the hind legs drawn straight out behind. The prolapse is placed between the extended limbs. In fresh cases, replacement is relatively easy and is begun at the cervical pole of the organ; the dorsal and ventral parts are massaged alternately back into their normal position. After the ovarian pole has been replaced, the previously prolapsed horn must be straightened and eversion of the uterus corrected; this can be done manually or by intrauterine infusion of warm saline. Administration of clen- buterol is reported to relax the uterus, facilitate replacement, and reduce the need for epidural anesthesia, but its use is illegal in the United States. If the patient has been neglected, accumulated fluid must be reduced by lubricating the tissue with an emollient ointment and then carefully but vigorously massaging the tissue from the ovarian pole toward the cervical pole. The hygroscopic action of sugar when applied liberally to prolapsed uteri is of questionable value.

Oxytocin (5 to 40 IU IM or IV) is frequently administered to stimulate myometrial contractions after the uterus has been replaced. Metritis is a frequent sequela, and appropriate antibiotic treatment is indicated in most cases. Temporary closure of the vulva with heavy sutures after replacement may not be necessary but is practiced by many clinicians. If replace­ment of the prolapsed uterus is impossible or the tissue is severely traumatized, amputation may be indicated; in this case it is important that the uterine arteries be double ligated.²⁰ Euthanasia may also be considered in such instances.

The prognosis varies but is generally favorable if there has been no serious damage to the uterus. Fatalities can occur in cases complicated by shock or by rupture of large uterine vessels. The culling rate from infertility of cows with uterine prolapse is higher than that of their herdmates, and the calving interval is prolonged in affected cows. Barring hypocalcemia, the risk of uterine prolapse at a subsequent calving is no greater than for other cows in the herd.

■ Prevention and Control Because the condition is associated with hypocalcemia in cows, provision of a properly balanced ration before calving is indicated. Although uterine prolapse can occur after an apparently normal delivery, it is more commonly associated with dystocia and forced extraction; therefore prolapse should be anticipated, and the dam observed so that affected patients may receive prompt treatment. Oxytocin (5 to 40 IU IV or IM) may be administered after a dystocia to increase uterine tone and potentially prevent prolapse.

■ Camelids Uterine prolapse in camelids is usually a consequence of dystocia, RFMs, or excessive obstetric manipula­tion. Treatment is the same as described for other species.

Uterine Tumors

Neoplasia uncommonly affects the uterus of domestic animals. Leiomyomas are usually benign and arise from the outer smooth muscle of the uterus without need for a preparatory event. Leiomyomas are not necessarily associated with reproductive failure, and tumors and fetuses can coexist.

The multicentric form of lymphosarcoma may affect the uterus of cattle. Lymphosarcoma also affects does, but a predilec­tion for the uterus is not apparent. Uterine walls affected by lymphosarcoma may contain discrete neoplastic nodules or be diffusely infiltrated.

Carcinomas, chorionepitheliomas, fibromas, fibrosarcomas, rhabdomyosarcomas, and adenosarcomas are rarely reported. Regardless of tumor type, tumors must be differentiated from normal fetuses, mummified or macerated fetuses, placentomes, abscesses, and fat necrosis.

Segmental Defects

Segmental aplasia (white heifer disease) occurs sporadically in all breeds of cattle. In most cases the cranial parts of the genital tract (ovaries, uterine tubes, and cranial part of the uterine horns) are normal, and endometrial secretions from the parts of the uterine horns accumulate because normal drainage through the cervix is impeded. Various defects may be found in affected animals, ranging from nearly complete absence of tubular genital organs to an imperforate hymen that blocks secretion drainage from a normal genital tract.

■ Clinical Signs and Diagnosis Segmental aplasia may be associated with a history of anestrus if fluid accumulation within the uterine horns interferes with release of PGF_2α and luteolysis. Other presenting history may involve infertility or difficulty in AI. On palpation per rectum, various degrees of aplasia may be recognized. Fluid-filled parts of the uterine horns may suggest pregnancy, from which they must be dif­ferentiated. An imperforate hymen may bulge from the vulvar cleft and may be confused with vaginal prolapse, prolapse or eversion of the urinary bladder, cystic vestibular glands, or neoplasia of the vulva or vagina.

■ Treatment and Prognosis The only form of segmental aplasia amenable to treatment is that in which an imperforate hymen occludes an otherwise normal tract. Incision of the hymen is followed by drainage of accumulated secretions and may allow the tract to function normally.

Paramesonephric Duct Aplasia

Aplasia of one paramesonephric duct leads to development of one uterine horn (uterus unicornis). The condition is found in cattle but is rare. Subfertility is the result of prolonged periods of anestrus caused by a persistent CL on the ovary ipsilateral to the missing uterine horn (no local luteolytic signal). The condition can be managed with exogenous PGF_2α in the hope that ovulation will occur on the intact side. Alternatively, the unaccompanied ovary can be surgically removed.

Uterus Didelphis

The caudal parts of the paramesonephric ducts may not fuse properly in cattle, causing duplication of various parts of the caudal tubular tract. Abnormalities of fusion are most common in and around the cervix. The entire cervix may be duplicated, or the cervix and vagina may be normal, with the exception of the presence of a band of tissue extending dorsal to ventral across the external os of the cervix. Partial failure of fusion may involve a part of the cervix, and the affected animal may possess a single uterine body and internal cervical os, duplication of a part of the cervical canal, and a doubled external cervical os. Uterus didelphis results when the cervix and uterine body are completely duplicated. Affected cows may conceive after natural service or if artificially inseminated through the cervix and uterine horn ipsilateral to the ovary about to ovulate. Affected animals may be unable to carry a pregnancy to term because of lack of placental attachment in the nongravid horn.

Hydrometra (Pseudopregnancy in Small Ruminants)

Hydrometra occurs sporadically in sheep and goats and is characterized by accumulation of several liters of clear fluid within the uterus, abdominal distention, persistence of a CL, and subsequent anestrus.²⁰ Previous breeding is not necessary, but the condition may develop after mating, and does are frequently assumed to be pregnant. It can also occur after early embryonic loss in goats or sheep. The cause of hydrometra is unknown, but a deficiency in production or release of PGF_2α from the endometrium has been postulated, as has exposure to phytoestrogens. The clinical signs of hydrometra mimic those of pregnancy. The diagnosis is suspected if the goat fails to show estrus when it cannot possibly have been bred but is in a herd where heat detection is good. Serum progesterone concentrations are elevated, and abdominal enlargement sug­gestive of pregnancy may occur. Blood-based biochemical pregnancy markers will be negative. Amplitude-depth ultrasound for pregnancy is positive because of fluid in the uterus. Trans­abdominal ultrasound reveals anechoic fluid but no fetus or caruncles in the uterus. The animal should be rechecked if fewer than 40 days have elapsed since the last possible breeding, as early pregnancy is possible in such cases. In advanced hydrometra, large anechoic fluid-filled compartments are seen separated by undulating tissue walls, which represent the uterus coiled back on itself. Spontaneous correction is common and varies from red discharge suggestive of early abortion to expulsion of accumulated fluid approximately 150 days after

an infertile mating, so-called cloudburst. No fetus or placenta is passed. Treatment of false pregnancy is with prostaglandin. The clinician needs to keep in mind that this will induce abortion if the ewe or doe has a true pregnancy. An initial dose of 5 to 10 mg of dinoprost (Lutalyse) or 125 to 250 μg of cloprostenol (Estrumate) is given and repeated in 12 days. Estrus and emptying of the uterus occur in 1.5 to 4 days. Oxytocin (50 IU bid for 4 days) is normally reserved for females that retain fluid in the uterus after prostaglandin therapy. The doe frequently becomes pregnant within a few days to weeks after termination of a false pregnancy if a buck is available. Sometimes hydrometra recurs. Suggestions for prevention have included selenium supplementation and breeding on the first heat of the season. The prevalence is surmised to be increased in herds where breeding is delayed in order to obtain winter milk and in does manipulated hormonally to breed out of season.²⁰ Routine pregnancy diagnosis of sheep and goats with transabdominal ultrasound should be advised to permit rebreed­ing during the same season.

Cervical Abnormalities

Cervicitis

Inflammation of the cervix usually accompanies endometritis and vaginitis and is frequently secondary to trauma associated with dystocia and obstetric operations. The mucus-secreting epithelium of the cervix is more resistant to bacterial infection than is the epithelium of the uterus and vagina.

■ Mares The equine cervix is a straight tube made up of layered circular and longitudinal muscle. During estrus it relaxes, and the external os lies on the floor of the anterior vagina. During diestrus or pregnancy, under the influence of proges­terone, the cervix is closed and the external os is elevated off the vaginal floor. Cervicitis or inflammation of the cervix may be iatrogenic or may occur secondary to trauma associated with parturition or dystocia or as an extension of vaginitis or endometritis. Endometritis and infertility follow if the cervix lacks anatomic integrity.

■ Clinical Signs and Diagnosis Infertility and history of an inciting cause such as urine pooling or dystocia may be the only signs of cervicitis in the mare. Cervical hyperemia and edema may be apparent on speculum examination in acute cervicitis. In more chronic injuries, direct digital examination of the cervix of the mare in diestrus may reveal transluminal adhesions or anatomic defects.

For treatment and prognosis in mares, see discussion under Ruminants.

■ Ruminants Similarly, in cows cervicitis is secondary to uterine infections and follows trauma associated with parturition and obstetric manipulations. Infection is usually caused by microorganisms normally present in the cranial vagina such as E. coli, streptococci, staphylococci, and T. pyogenes.

Cervicitis in does and ewes is uncommon but may occur secondary to vaginal and uterine infections and obstetric trauma.

■ Clinical Signs and Diagnosis Examination of cows with a vaginal speculum reveals swelling and edema of the external cervical os. The mucous membrane is hyperemic and inflamed. Mucopurulent exudate may be present in the cervical canal or in the cranial vagina. Hypertrophy of the cervix is common in Bos indicus breeds and their crosses and may be a normal finding; therefore cervical size as detected by palpation per rectum may or may not indicate inflammation. Inflammation of the cervix without contemporary endometritis may not affect fertility. Cervicitis may occur in pregnant cows.

The clinical signs of cervicitis in does and ewes are similar to those in cattle and must be observed with a small vaginal speculum.

■ Treatment and Prognosis Most cases of cervicitis resolve spontaneously when coexisting endometritis and vaginitis improve. Exudate can be flushed from the cervical canal and cranial vagina with warm saline lavages, and a nonirritating antibiotic ointment applied to the affected tissue. Caustic chemi­cals should not be placed in contact with the cervical mucosa. Aggressive treatment with systemic antibiotics is indicated in cases complicated by infection with anaerobic bacteria.

The prognosis for most cases of simple cervicitis is fair to good. However, inflammation of the cervix in mares may progress to more severe cervical abnormalities. Cervical damage is a serious threat to future reproductive performance in mares. Anaerobic infections of the cervix may be fatal.

■ Prevention and Control Obstetric manipulations and operations must be temperate. When the cervix does not dilate properly during parturition, a cesarean section is preferred over forced extraction.

Cervical Lacerations

■ Mares Cervical lacerations are most often seen after dystocia. The condition may result in adhesions and a nonpatent cervix or in failure to seal the uterus during diestrus or preg­nancy. Cervical adhesions in combination with endometritis are a common cause of pyometra in the mare.

■ Clinical Signs and Diagnosis Cervical lacerations can be diagnosed by vaginoscopy and digital examination of the cervix. A digital examination of the cervix is often necessary to evaluate the degree and severity of the laceration. Evaluation of the ability of the cervix to close adequately is best performed during diestrus.

■ Treatment and Prognosis If cervical lacerations are diagnosed shortly after parturition, antimicrobial ointment should be applied frequently to the lesion. Early signs of adhesions should be broken down until the tissue is healed. If the laceration results in an incompetent cervix, it should be corrected surgically. Although surgical repair of cervical lacera­tions has resulted in restored fertility in many mares, the condition is likely to recur at the time of the next parturition. Embryo transfer should be considered if allowed by the breed registry.

Vaginal Abnormalities

Pneumovagina

MARES. Pneumovagina is characterized by aspiration of air, often containing microorganisms, into the vagina. Pneu­movagina is secondary to changes in perineal conformation, which include cranioventral displacement of the reproductive tract, loss of integrity of the vestibulovaginal sphincter, and loss of integrity of the vulvar labia. These changes occur more commonly in older, multiparous mares and those that have had perineal lacerations. Pneumovagina is a common antecedent to infertility.

■ Clinical Signs and Diagnosis In the normal mare, the anus is positioned directly dorsal to the vulva. The perineal body between the dorsal vulva and the anus is thick, muscular, and well formed. The vestibulovaginal sphincter is well formed, and the vulva has a vertical alignment, with 80% of the vulval labia situated below the floor of the pelvis. The vulvar labia form a seal in the normal mare.

Mares prone to pneumovagina are those in which the vulva tilts horizontally at its dorsal aspect, the perineal body is thin, the vulval labia do not form a seal, and the anus lies cranial to the vulva. A scoring system has been developed to evaluate the perineal conformation in mares.¹ The system uses Caslick's index, which equals the distance (in cm) between the dorsal commissure of the vulva and the pelvic floor multiplied by the degrees of declination of the vulvar lips. Mares with a Caslick's index above 150 were found to have subnormal pregnancy rates. Affected mares aspirate air on exercise or when the vulval labia are parted. Aspirated air may be noted on transrectal palpation or vaginal speculum examination. Signs of secondary changes such as vaginitis, cervicitis, or endometritis may be apparent.

■ Treatment and Prognosis Treatment of pneumovagina should be directed toward correcting defective perineal confor­mation. Cranioventral displacement of the reproductive tract in aged mares may be irreversible. Perineal confirmation in thin mares is often improved by increasing the mare's body condi­tion. Pneumovagina is often successfully corrected by surgical closure of the dorsal vagina via Caslick's surgery. Secondary changes should be treated as described elsewhere. Prognosis for correction of pneumovagina is excellent; however, prognosis for fertility depends on the extent of secondary changes.

Urovagina

MARES. The normal vagina in young mares slopes cra- niodorsally and is largely contained within the pelvis. With aging and repeated pregnancy, the cranial vagina may slope cranioventrally and fall below the level of the pelvic floor. Under these conditions urine collects in the anterior vagina. Urine is spermicidal, and the condition is often associated with subfertility.

■ Clinical Signs and Diagnosis In mild cases, a history of infertility may be the only indicator of urovagina. In more severe cases, urine dribbles from the vulva at rest or during exercise and may accumulate on the skin of the hindlimbs. Speculum examination reveals a cranioventral slope of the vagina, variable inflammation of the cranial vagina and cervix, and a pool of urine in the ventral vaginal fornix. Urovagina may occur intermittently or only during estrus.

■ Treatment and Prognosis Surgical procedures to prevent the anterior flow of urine include urethral extension² and vaginoplasty. Prognosis depends on the severity of second­ary endometritis and the success of surgery.

Vaginitis

Vaginitis may occur as a result of ascending infection or exposure to irritants, or secondary to pneumovagina, urovagina, perineal laceration, rectovaginal fistulas, breeding, endometritis, abor­tion, parturition, or dystocia. Occasionally, traumatic wounds may be infected with clostridial or anaerobic organisms; however, most infection is nonspecific.

■ Clinical Signs and Diagnosis Signs may vary from hyperemia evident on speculum examination to mucopurulent exudation from the vulva. Severe trauma and infection may be followed by necrotic vaginitis with tenesmus, fetid discharge, elevated tail, swollen vulva, and systemic signs. Rapid formation of adhesions follows necrotic vaginitis. Metritis, RFMs, and uterine tears also may show systemic signs and vaginal discharge.

■ Treatment and Prognosis The inciting cause should be treated. Animals with mild vaginitis may recover spontane­ously, whereas moderate cases require lavage with dilute antiseptic or antibiotic solutions. Fertility is unaffected in mild vaginitis without extension, and prognosis is good. Severe, necrotic vaginitis is treated with systemic antibiotics, analgesics, and antiinflammatory agents. Caslick's surgery may be necessary to prevent aspiration of air. Local application of antibiotic and steroid-impregnated ointments may help prevent adhesions. Prognosis for severe vaginitis is guarded. Vaginal stenosis and adhesions may follow vaginitis.

■ Prevention and Control Nonspecific vaginitis may be prevented by reducing trauma to the vagina during foaling. Clinicians should elect appropriate methods for relief of dystocia and apply extractive force to fetuses judiciously.

Infectious Pustular Vulvovaginitis

COWS. Infectious pustular vulvovaginitis (IPV) affects cattle and is caused by bovine herpesvirus 1, also the cause of infectious bovine rhinotracheitis (IBR), although the two strains are genetically distinct.⁴ Therefore the respiratory and genital forms of the disease rarely occur concurrently, and abortions usually do not follow an outbreak of the genital form of the disease. IPV is spread by coitus and mechanical means and may affect unbred heifers. The incubation period of IPV is short (1 to 3 days), and the infection spreads rapidly through the herd, affecting 60% to 90% of the animals.

■ Clinical Signs and Diagnosis Early in the course of the disease, IPV is characterized by a mucopurulent vaginal discharge, inflammation of the vaginal and vulvar mucosa, and painful urination. Pustules develop over lymphoid follicles and progress from small (to carry both fetuses to term and deliver without dystocia.² It is much more common for the mare to have a natural reduction to a singleton pregnancy during the embryonic stage or to abort the pregnancy after the fetal stage.^3,4 Some breeds are more commonly diagnosed with twins during the embryonic stage (e.g., Thoroughbreds have 20% to 30% double ovulations and 10% to 15% diagnosed twin pregnancies).

■ Clinical Signs and Diagnosis Mares should be evalu­ated with transrectal ultrasound 13 to 15 days after documented ovulation during a breeding cycle. The ovaries should be examined for more than one active CL, and the uterus should be carefully scanned from the tip of one horn to the other and along the uterine body to the cervix. Equine embryos at this stage are highly mobile within the uterus and may be located anywhere within the uterus. Twin pregnancy should not be ruled out until the entire uterine tract has been scanned for the presence of embryos. After one embryo is found, the remainder of the uterus still must be visualized to ensure the absence of a twin. The embryo proper per se is not visible at this stage of pregnancy, but the embryonic vesicle is easily visualized. Care must be taken not to confuse endometrial cysts with embryos, which sometimes can look deceptively similar. It is helpful to have scanned the mare's uterus using ultrasound before breeding to document the size and location of endometrial cysts.

■ Treatment and Prognosis If twins are confirmed before 16 days of pregnancy, the best way to treat the mare is to manually crush one of the vesicles. This is done by visualizing the twins using transrectal ultrasound and spatially separating them from each other within the uterus. One twin is moved away from the other to the tip of a uterine horn, where it is crushed manually. The remaining embryo should be evaluated 1 to 2 days later to determine its status. Manual reduction of an embryo fixed in the contralateral horn from its twin between days 16 and 20 should be performed at the base of one uterine horn, because embryos are typically “fixed” at this site after day 16. Survival of the remaining embryo is greater than 90% when twin reduction is performed in this manner before day 20.⁵

■ TABLE 43.7

Major Causes of Infectious Equine Abortion

PCR, Polymerase chain reaction.

It is the established practice of some veterinarians to treat mares with a nonsteroidal antiinflammatory agent (e.g., flunixin) and/or altrenogest after a twin-crush procedure. The reasoning behind this practice is that manual stimulation of the uterus may cause a release of oxytocin, signaling a prostaglandin cascade that will result in luteolysis and complete pregnancy loss. No studies have been performed to support this theory; to the contrary, other studies have shown that the release of prostaglandin after the routine twin-crush procedure does not cause a drop in progesterone and that supplementation with antiinflammatory drugs or progesterone makes no difference in the outcome.^5,6

Twins fixed next to each other at the base of the same horn between days 16 and 20 cannot be separated from each other. Manual reduction can still be reliably performed at this stage but will result in the loss of both embryos and the need to breed the mare again on a subsequent cycle. If twins are discovered fixed ipsilaterally between days 16 and 20, the practice of “benign neglect” may be followed for a short time. Since most of these situations will resolve naturally with the resorption of one twin and the persistence of the other, it is a responsible practice to simply monitor the situation to note if one twin regresses. If both twins continue to develop approaching the formation of endometrial cups (day 37 to 38), a decision must be made either to terminate the pregnancy or to refer the mare for advanced, selective twin reduction, which includes transvaginal, ultrasound-guided fetal aspiration⁷; transcutaneous, ultrasound-guided fetal intracardiac injection of procaine penicillin or potassium chloride⁸; or craniocervical dislocation.⁹ The success of these techniques is lower than that of manual crush, and they are performed later in gesta­tion, after the window for manual crushing has been missed. These are all specialty techniques and are beyond the scope of this chapter.

Other Noninfectious Causes of Equine Abortion

In a survey of causes of equine abortion in the United Kingdom from 1988 to 1997, nearly 39% were caused by umbilical cord pathology.¹⁰ Most of the cases (35%) resulted from torsion of the umbilical cord. Twisting of the umbilical cord is common in equine fetuses and often is not pathologic. A diagnosis of abortion caused by umbilical torsion should be made only if localized swelling and discoloration accompany the twisting. Congenital abnormalities may cause abortion. The most common congenital abnormality in equine fetuses is contracted tendons, accounting for 5% of abortions in a study from the United States.¹ Fetuses that implant in the uterine body instead of the base of one of the horns develop placental villous atrophy and usually abort, accounting for 2% of abortions in the same study.

Infectious Causes

Placentitis

Placentitis is the leading cause of equine late-term pregnancy loss in the United States.¹ Bacterial organisms most commonly cultured from aborted fetuses include Streptococcus spp., E. coli, Pseudomonas spp., Klebsiella spp., Staphylococcus spp., and Leptospira spp. Nocardioform actinomycetes are an important cause of placentitis in central Kentucky and have also been reported in Florida.^11-13 Aspergillus fumigatus and Mucor spp. are the most commonly diagnosed causes of mycotic abortion in mares, causing 5% to 30% of infectious equine abortions.

The route of placental infection is believed to most com­monly be ascending via the cervix, which results in loss of chorionic villi around the cervical star. In addition to loss of chorionic villi, additional allanto chorionic lesions may include nodular cystic allantoic masses, edema, necrotic areas of chorion, and necrotic mucoid exudate coating the chorion. Hematogenous placentitis shows a more generalized, diffuse loss of villi.¹ Infection of the placenta results in subsequent infection of the fetus and release of proinflammatory cytokines and prostaglandins from the inflamed placenta, which ultimately leads to mid- to late-term abortion or delivery of a premature foal.¹⁴ The distribution of the avillous chorionic lesion classically noted in mares with ascending or hematogenous placentitis does not fit the pattern noted with nocardioform placentitis. Mares with nocardioform placentitis classically show a loss of chorionic microvilli, covered by brownish, thick, and tenacious exudate in a focal area around the ventral aspect of the uterine body and base of the uterine horns.

The pathogenesis of nocardioform placentitis is still unre­solved. It has been hypothesized that the pathogen is present in the environment or introduced into the mare at the time of breeding and settles in the ventral aspect of the uterus, where infection ensues. Various nocardioform organisms have been reported in soil across the globe, although the pathogenic­ity of most of these organisms has not been determined. Nocardioform organisms isolated from equine placentas include Amycolatopsis spp. and Crossiella equi.ⁱⁱ∙ⁱⁱ∙ⁱ⁵∙ⁱ⁶ These bacteria have been diagnosed only from clinical cases of placentitis and not from the environment.¹⁷ Nocardioform placentitis often results in abortion or premature delivery.¹ Bacteria and resulting inflammation are limited to the interface between the chorion and the endometrium. Because no bacterial invasion or signs of inflammation have been observed in the placental and fetal tissues, the abortion is postulated to be due to nutritional deprivation of the fetus resulting from separation between the chorion and endometrium.

■ Clinical Signs and Diagnosis Premature udder development and vaginal discharge are common signs of pending abortion caused by ascending placentitis. However, when these signs are present, the prognosis is poor even when mares are treated. Transrectal ultrasonography of the allantochorion in an area close to the cervix is useful to detect early signs of placentitis and impending abortion (Fig. 43.6).¹⁸ Ultrasound evaluations may reveal hyperechoic fetal fluids, placental separation, increased or decreased fetal heart rates (normal range 75 ± 7 bpm¹⁹), and thickening of the combined thickness of the uterus and placenta (CTUP). Consistently low or high fetal heart rates are associated with fetal stress. Foals experienc­ing fetal distress often become bradycardic initially and then become tachycardic in the terminal phase of life.^20,21 Serial examinations should be performed to verify fetal well-being or distress. Mares considered “at risk” for pregnancy loss are often examined daily. Fetuses experiencing distress are often evaluated several times a day. Normal measurements of CTUP have been established (Fig. 43.7).^18,22 Mares with placentitis may show increased CTUP, edema of the allantochorion, and separation from the endometrium. A 5-MHz linear transducer should be used for transrectal ultrasonography. The transducer should be positioned 1 to 2 inches cranial to the cervical- placental junction and then moved laterally until a major uterine vessel is visible at the ventral aspect of the uterine body.²² The CTUP should then be measured between the vessel and the allantoic fluid (see Fig. 43.6). It is important to obtain all CTUP measurements from the ventral aspect of the uterine body, because physiologic edema of the dorsal aspect of the allantochorion has been noted in normal pregnant mares during the last month of gestation.²² In addition, care should be exercised to be certain that the amniotic membrane is not adjacent to the allantochorion because this may result in a falsely increased CTUP. To examine the placenta from a transabdominal approach, a 3.5-MHz sector transducer is used most frequently. All four quadrants of the placenta should be examined: right cranial, right caudal, left cranial, and left caudal. Measurements of the CTUP can be made with this technique

FIG. 43.6 Transrectal imaging of the combined thickness of the uterus and placenta (CTUP). Measurements of the CTUP (distance between + and +) were recorded from the ventral part of the uterine body, close to the cervix. a, Placenta adjacent to the cervix; b, allantoic fluid; c, amniotic fluid; d, the amnion. (Modified from Renaudin CD, Troedsson MH, Gillis CL, et al.: Ultrasonographic evaluation of the equine placenta by transrectal and transabdominal approach in the normal pregnant mare. Theriogenology, 47:559, 1997.)

FIG. 43.7 Monthly recordings of transrectal ultrasonographic measurements of the combined thickness of the uterus and placenta (CTUP) in normal mares from 4 months of gestation and throughout the pregnancy. Month 4 is 91 to 120 days; month 5 is 121 to 150 days; month 6 is 151 to 180 days; month 7 is 181 to 210 days; month 8 is 211 to 240 days; month 9 is 241 to 270 days; month 10 is 271 to 300 days; month 11 is 301 to 330 days; month 12 is 331 to 360 days. (Modified from Renaudin CD, Troedsson MH, Gillis CL, et al.: Ultrasonographic evaluation of the equine placenta by transrectal and transabdominal approach in the normal pregnant mare. Theriogenology 47:559, 1997.)

if the fetus is not in close apposition with the uterine wall. Mares with normal pregnancies should have a minimum CTUP of 7.1 ± 1.6 mm and a maximal CTUP of 11.5 ± 2.4 mm.²³ Pregnancies with an increased CTUP have been associated with the delivery of abnormal foals.²³ False-positive results have been reported, and clinical judgment should be exercised before treatment is implemented. Placental separation and purulent material at the ventral aspect of the base of the gravid horn and the uterine body can be observed in mares with nocardioform placentitis. This finding can be identified only by using transabdominal ultrasound.

The gross lesions of the fetus are not specific. An increased amount of fluid in the thoracic and abdominal cavities and an enlarged liver are frequently observed in aborted fetuses. Placental lesions in cases of ascending placentitis are most severe on the chorionic surface at an area from opposite the cervix (“cervical star”) to the body of the placenta. The affected area is edematous, thickened, and discolored or brown with a mucoid or fibronecrotic exudate on the surface. The placenta is characteristically thickened and leathery in cases of mycotic placentitis, with lesions well demarcated from the rest of the chorionic surface. Microorganisms can be isolated from the placenta and several fetal organs, most consistently from the stomach.

Mares with nocardioform placentitis may have premature mammary development but will not have vulvar discharge, owing to the location of the infection. Placental lesions in mares infected with Amycolatopsis spp. and C. equi are located ventrally in the uterine body and at the base of the uterine horns. Affected areas are avillous, thickened, and covered by thick brown or reddish exudate. Differential diagnoses for this clinical presentation include twins and Cellulosimicrobium cellulans 15

placentitis.¹⁵

Prevalence of fungal abortions varies greatly with region. The most common route of fungal infection is ascending via the cervix, and fungal infections may be seen with a mixed bacterial infection. Abortions are observed from mid to late gestation. The chorion generally shows marked evidence of placentitis with edema, thick plaques, and a thick, mucoid exudate. In rare cases, amniotic thickening may be noted. The aborted fetus is often small and emaciated owing to chronic placental insufficiency. Culture of the chorion may be diagnostic but takes time. Culture of the fetus is rarely rewarding. Impres­sion smears of the chorion, as well as sometimes the fetal stomach, may reveal hyphae.

PROGESTERONE. The equine placenta is part of an endocrine fetal-placental interaction that synthesizes and metabolizes progestagens.²⁴ This endocrine function of the placenta is important for maintenance of pregnancy after the endometrial cups and the secondary corpora lutea disappear at approximately day 120 to 150 of gestation. Fetal-placental progesterone is rapidly metabolized to 5α-pregnanes. Mares with placental pathology may have increased plasma concentrations of pro­gestagens as a result of stress to the fetal placental unit.^25,26 Unfortunately, 5α-pregnanes are not readily assayed in a commercial setting, so diagnosis of placental disease using 5α-pregnane concentrations is not possible. There is cross­reactivity between 5α-pregnanes and progesterone using some commercial radioimmunoassays for progesterone. Using an experimental model to induce placentitis, it was found that mares that develop a chronic form of placentitis also develop increased plasma progesterone concentrations.^26,27 Conversely, mares that developed acute placentitis and abortion soon after infection experienced a rapid drop in plasma progesterone concentrations. It has been suggested that serial measurement of plasma progestin concentrations in mares with placentitis might be a useful method to identify mares that may abort or deliver prematurely.²⁶ However, in a recent prospective study

of 700 mares in central Kentucky, with blood collected weekly until the end of pregnancy, progesterone concentrations in the sample obtained during the week preceding abortion were not significantly different from those in mares with normal pregnancy outcome.²⁸ Sensitivity of progesterone assays can be improved when they are combined with evidence of placental thickening as detected using transrectal ultrasonography.²⁷

ESTROGEN. Serum estrogen concentrations are deviated in pregnant mares between 150 and 310 days of gestation.²⁹ The predominant estrogens in pregnant mares are estrone, equilin, equilenin, estradiol-17β, and estradiol-17α. Douglas²⁹ observed that mares aborting from placentitis had serum estrogen concentrations below those normally detected in pregnant mares. These observations were supported by results from a recent prospective study, in which low estradiol-17β sulfate serum concentrations were significantly associated with abnormal pregnancy outcome.²⁸ Based on these findings, it was suggested that supplementation with estradiol cypionate (ECP) or estradiol-17β may prevent abortion in mares with placentitis, but this has not been supported by later research.³⁰

RELAXIN. Relaxin is produced by the equine placenta and can be detected in peripheral blood plasma from day 80 of gestation and then throughout the pregnancy. The role of relaxin during pregnancy is not fully understood, but there is some evidence that placental relaxin production is compromised in mares at risk of aborting their fetuses.³¹ There currently is no commercial test available for equine relaxin.

ADDITIONAL MARKERS FOR PLACENTITIS

Acute Phase Proteins. Serum amyloid A (SAA) remains low throughout gestation but shows a significant increase within 12 hours of parturition and returns to baseline within 60 hours postpartum.³² Interestingly, levels of SAA in peripheral blood have also been reported to increase in mares with experimentally induced placentitis.³³ However, SAA is a nonspecific marker of inflammation with significant increase observed during other sources of inflammation and even after vaccination. Further­more, only a weak association was detected between pending abortion and elevated SAA concentrations in a prospective clinical study.²⁸

Serum Alpha-Fetoprotein (AFP). Elevated AFP has been associated with abnormal pregnancy outcome under clinical conditions, and this protein may be used as a marker for mares with placentitis and/or at risk of aborting.²⁸ In summary, no single test appears to have sufficient specificity, sensitivity, or practicality to accurately detect early subclinical cases of placentitis. A panel of estradiol-17β, AFP, and SAA may serve as the best available method to screen mares for unhealthy pregnancies as well as predict the outcome.

■ Treatment and Prognosis Treatment efforts should be directed at combating infection, reducing inflammation, and controlling myometrial activity. Pregnant mares with clinical signs of placentitis should be treated with systemic broad­spectrum antimicrobials and antiinflammatories. Commonly used antibiotics such as penicillin G sodium or potassium (22,000 IU/kg IV q6h), gentamicin (6.6 mg/kg IV q24h), and trimethoprim-sulfadiazine (30 mg/kg PO bid) cross the placenta and reach therapeutic concentrations in both placental tissues and the allantoic fluid.³⁴ However, the duration of these elevated concentrations was short and below that in blood plasma. This may explain why more than 60% of mares that had been treated for placentitis still cultured positive on endometrial biopsy after foaling.³⁵ It may also explain why antibiotic treatment appears to be necessary for the remainder of gestation in mares with placentitis. Flunixin meglumine (1.1 mg/kg IV or PO q12h) and pentoxifylline (8.5 mg/kg PO bid) have been used to control proinflammatory cytokines associated with placentitis. Treatment with progestins has long been advocated to promote uterine quiescence in mares with uterine pathology. Presumably the anti-prostaglandin effect of progestins contributes to reduced myometrial activity by interfering with upregulation of pros­taglandin and oxytocin receptors.³⁶ Altrenogest at twice the recommended dose (0.088 mg/kg PO q24h) is commonly used.

The efficacy of multimodal, long-term therapy for equine placentitis has been investigated in a large-scale clinical trial.³⁷ Investigators examined records of 477 mares over 6 years. Fifteen mares were diagnosed with placentitis. Criteria for treatment included increased thickness of the uteroplacental unit using transrectal ultrasound, placental separation, and/or vulvar discharge and udder development. The average gesta­tional age at diagnosis was 8.6 months. Mares were treated until abortion or delivery of foal with a combination of systemic antibiotics (trimethoprim-sulfa, ceftiofur, or penicillin and gentimicin); pentoxifylline; altrenogest; and nonsteroidal antiinflammatory agents. Twelve of 15 treated mares (80%) carried their foals to term, and 11 of 15 (73%) delivered live foals. Birth weights of surviving foals from mares treated for placentitis were similar to those of foals from nonaffected mares. The benefit of this treatment strategy is supported by more recent data from a controlled study on experimentally induced placentitis.³⁸ Therefore long-term antibiotic, antiinflammatory, and progestin treatment may positively affect pregnancy outcome in mares with placentitis.

Although most mares are capable of conceiving and suc­cessfully carrying a foal to term in subsequent breedings, reproductive performance may be negatively affected after placentitis, be it induced by the ascending or hematogenous route. Treatments for endometritis, such as uterine lavage and intrauterine infusions of appropriate antibiotics, should be implemented after abortion. Most mares affected by nocar­dioform placentitis do not require subsequent treatment and show no signs of infertility the following breeding season.

Equine Herpesvirus 1 Abortion

The most prevalent viral cause of equine pregnancy loss is equine herpesvirus 1 (EHV-1), which causes abortion, paresis, and neonatal foal death. EHV-4 causes abortion in rare cases. The primary route of transmission of EHV-1 is via the respira­tory tract. The virus invades the respiratory epithelium and establishes a leukocyte-associated viremia. EHV-1 establishes a chronic, possibly lifelong, latent infection. During the initial infection, placental endothelial cells are infected by the virus and transiently present targets to the immune system as the cells present viral particles. The virus eventually inactivates the major histocompatibility complex 1 (MHC-1) ability of the cells to present viral particles, thus evading the immune system.³⁹ After respiratory infection, EHV-1 causes an episode of viremia and infects the fetus via transplacental migration of virus-bearing leukocytes. Respiratory clinical signs in infected mares may be subclinical. The time between infection and abortion varies greatly from less than 2 weeks to several months.⁴⁰ Abortion occurs as a result of a rapid separation of the placenta, causing suffocation of the fetus.⁴¹ Near-term fetuses may be born alive but will die within days. Aborting mares clear the virus quickly from the reproductive tract, and subsequent fertility is often not affected by the disease. Clinical signs and fetal lesions of abortion caused by EHV-1 and those caused by EHV-4 are indistinguishable from each other.⁴⁰

As with all herpesviruses, EHV-1 establishes a latent infection that may recrudesce after stressful events, such as weaning, translocation, introduction of a new animal, or other illnesses. It is unclear whether a reactivation event will cause an abortion, but this is considered likely.⁴² Recrudescent infections are certainly transmissible. Aborted, infected fetal materials are also highly contagious. Both of these sources may be responsible for abortion epizootics. Although epidemic abortions occur, losses may be confined to only a few mares in a herd.

■ Clinical Signs and Diagnosis The primary lesion of EHV-1 is necrotizing vasculitis and thrombosis resulting from lytic infection of the capillary endothelium. The fetus may become infected or remain uninfected, depending on whether the virus crosses the uteroplacental barrier. If transplacental fetal infection occurs late in gestation, a live, infected foal may be born but will not usually survive. Stage of pregnancy during which abortions may occur varies, but the vasculitis is most pronounced from the fifth to ninth months of gestation, and 95% of abortions occur in the last trimester of pregnancy.⁴³

Abortions occur suddenly as sporadic abortions or “abortion storms” without maternal clinical signs. The aborted fetus is fresh, with minimal signs of autolysis. Gross lesions in the fetus include increased fluid in the thoracic and abdominal cavities; congestion and edema of the lungs; hepatomegaly with multifocal, small (~1 mm), yellow-white necrotic foci; subcutaneous edema; and icterus. Histologically, the most characteristic lesion consists of areas of necrosis in lymphoid tissue, liver, adrenal cortex, and the lung, with large intranuclear eosinophilic inclusion bodies. In addition, a hyperplastic necrotizing bronchiolitis is often found. Lymphoid tissues are most commonly affected (nodes, thymus, spleen, and Peyer's patches). Other histopathologic lesions may include mild, multifocal, necrotizing lesions in the liver and adrenal cortex and a hyperplastic, necrotizing bronchiolitis. The placenta may be grossly normal or edematous with no specific microscopic lesions.⁴⁴

Laboratory diagnosis of EHV-1 abortion is done by either direct demonstration of virus (virus isolation or viral antigen) or viral nucleic acid detection (PCR) or indirectly through serologic evidence of recent infection. The placenta, lung, liver, spleen, and thymus should be collected aseptically in suspected cases of EHV-1 abortion for virus detection. Tissue samples for virus isolation should be kept at 4° C, not frozen at -20° C, until inoculated into cell culture. Samples that cannot be processed within a few hours after collection should be stored at -70° C. The identity of virus isolates recovered from tissue specimens must be confirmed by PCR, indirect immu- nofluorescent assays using EHV-1 specific antisera or mono­clonal antibodies, or neutralization assays using EHV-1 specific antisera or monoclonal antibodies. Serologic tests are not considered reliable in EHV-1 diagnosis. It should be kept in mind that serum from mares that aborted may already contain peak levels of antibodies, and no increase in titers will be detectable in subsequently collected sera. Equine fetuses have been found to be capable of producing antibodies to EHV-1 at 200 days of gestation. Maternal serology is of limited diagnostic value because mares may abort several weeks after infection. The rise in serologic titer may have disappeared by the time of the abortion.

■ Treatment and Prognosis Most studies do suggest a beneficial effect of vaccination, and the current recommendation is to vaccinate during the fifth, seventh, and ninth months of gestation.^39,43 Both killed and modified live vaccines are available. The vaccines are not fully protective, and abortion may occur in vaccinated mares. However, consistent vaccination of pregnant mares should be expected to decrease the incidence of abortion storms and sporadic abortions in a herd.

For the effectiveness of a vaccination program to be maxi­mized, it needs to be combined with a management strategy that minimizes exposure of mares to the virus and prevents activation of a latent viral infection. All horses—young, adult, nonpregnant, and pregnant—should be vaccinated to restrict shedding of the virus. Unnecessary stress such as transportation and overcrowding should be avoided. Pregnant mares should be kept separate from other horses on the farm. Newly arrived horses should be isolated from the resident population for 3 weeks, during which time they should be monitored daily for signs of respiratory disease.

After abortion, the fetus and fetal membranes should be transported away from the area without contaminating the surrounding environment. The stall in which the mare aborted should be disinfected with a phenolic or iodinophoric com­pound, and the bedding should be prevented from contaminating other areas on the farm. All pregnant mares on an infected farm should remain on the farm until they have foaled. No horse should leave the farm until 3 to 4 weeks after the last abortion.

Equine Viral Arteritis

Equine viral arteritis (EVA) is caused by equine arteritis virus (EAV). The primary target of EAV is the vascular endothelial cells and macrophages. Shortly after infection EAV can be found in the macrophages and later in the lymph nodes. The virus infects circulating monocytes and becomes systemic in distribution by 3 days after the primary infection, resulting in a carrier state (important in stallions). About a week after the primary infection, EAV infects the blood vessel endothelium and causes enough damage by 10 days after the primary infection to cause abortion. Abortion is likely caused by myometritis and vasculitis. Serum progesterone concentrations (produced exclusively by the placenta in the last half of equine pregnancy) fall to baseline levels before the abortion because of placental hypoxia.

Although the pathophysiology is not well established, fetal death may occur by fetal anoxia secondary to compression of myometrial vessels by edema and decreased progesterone production by the placenta.⁴⁵

■ History and Clinical Signs Clinical signs may be absent or highly variable and may include pyrexia, depression, anorexia, leukopenia, limb edema, stiffness of gait, rhinorrhea and epiphora, conjunctivitis, rhinitis, urticarial rash, localized or diffuse edema, and abortion. Abortion typically occurs at 3 to 10 months of gestation and follows the onset of clinical signs by several days up to 2 months. Abortion rates in outbreaks of EVA have varied from less than 10% to 71%. Less frequently, severe respiratory distress, ataxia, mucosal papular eruptions, submaxillary lymphadenopathy, and intermandibular and shoulder edema may be observed.⁴⁶ Infection is rarely fatal in adults but is more frequently fatal in neonates due to interstitial pneumonia and secondary bacterial infections. Clinical patho­logic findings are variable, inconsistent, and nonspecific and include hypoxia, hypercapnia, respiratory or metabolic acidosis, lymphocytosis or lymphopenia, neutrophilia or neutropenia, thrombocytopenia, and hyperfibrinogenemia. Gross and his­tologic lesions differ in severity with the virulence of the viral strain. Edema, congestion, and hemorrhage of the subcutaneous and lymphoid tissues and viscera are the most common gross lesions. Histologic lesions may be found in the vasculature, lymphoid tissues, lungs, intestines, adrenal glands, kidneys, and skin.⁴⁶ Abortion may occur without any clinical signs in the mare, and the fetus may be fresh or autolyzed. Fetal lesions are uncommon. The infected stallions may serve as long-term carriers, and virus may be transmitted in the semen.

■ Laboratory Diagnosis Laboratory diagnosis of EVA is currently based on any combination of virus isolation, viral nucleic acid or antigen detection, and serology. The most appropriate specimens for virus isolation from live horses include nasopharyngeal swabs or washings, conjunctival swabs, and citrated or ethylenediaminetetraacetic acid (EDTA) blood samples for separation of buffy coat cells. Placenta, fetal fluids, lung, spleen, and lymphoid tissues should be collected for virus isolation to confirm cases of EAV-induced abortion. Reverse transcription PCR (RT-PCR)-based assays (standard and real time) have several potential advantages over the current virus isolation procedure. Serologic diagnosis of EVA is based on virus microneutralization and is standardized by the World Organization for Animal Health (still known by the French abbreviation OIE for Office International des Epizooties) and described in the OIE manual. There are no characteristic lesions of EVA infection in the fetus, although autolysis and myocardial arteritis have been reported. An avidin-biotin complex (ABC) for immunoperoxidase staining using monoclonal antibodies to individual EAV proteins has been used successfully to detect viral antigens in formalin-fixed paraffin-embedded samples, as well as in frozen tissue sections.

■ Epidemiology and Control Transmission may occur venereally from persistently infected stallions to mares. Reproductive performance of venereally infected mares is not affected, but contact transmission from venereally infected mares to late gestational mares may cause abortion. Major outbreaks of EVA were reported in 1953, 1984, and 2006 in the United States. Apart from these incidents, occasional outbreaks have occurred, with abortion occurring at low incidence.⁴⁷ Mares may be isolated after infection but usually do not become carriers. A proportion of naturally infected stallions become persistently infected with EAV and shed the virus constantly in semen. Incidence of seropositive animals is higher in Standardbreds than in Thoroughbreds, and regula­tory guidelines may govern the use of seropositive Thorough­bred stallions. Carrier stallions may be the reservoir for the disease between outbreaks and should be isolated and bred only to immune mares. Mares bred in this way should be isolated for 3 weeks. A modified live-virus attenuated vaccine and a killed-virus vaccine are available for prevention of EAV infection in mares and stallions, although some local regulatory restrictions on use may exist. Vaccination of mares up to 3 months before foaling or in the postpartum period appears to be safe. Vaccinating pregnant mares in the final 2 months of gestation is associated with an increased risk of abortion, and decisions to vaccinate in this period must be weighed against concerns for widespread disease in naturally infected herds.⁴⁸ Control in stallions involves vaccination of seronegative stallions under the guidance of regulatory authorities.

Leptospirosis Abortion

Leptospirosis causes bacterial abortions in some areas and was reported to be responsible for 2.2% of abortions in a Kentucky study.⁴⁹ The serovar responsible shows regional variability. Serovar Leptospirapomona has most commonly been associated with leptospirosis abortion in mares, but Leptospira grippotyphosa, Leptospira hardjo, Leptospira bratislava, and Leptospira icterohemor- rhagiae have also been isolated from sporadic abortions.⁴⁹ Wet environmental conditions are considered important in the dissemination of the disease from wildlife to horses. Infected animals shed the spirochete in their urine, which contaminates groundwater and serves as a source for further infections. Many horses are seropositive for leptospires but are subclinical.

■ Clinical Signs and Diagnosis Clinical signs may include pyrexia, hemoglobinuria, jaundice, and abortion. Aborted chorioallantoic lesions are similar to those of other bacterial placentitis cases (nodular cystic allantoic masses, edema, necrotic areas of chorion, and necrotic mucoid exudate coating the chorion) but may show a diffuse pattern of distribution, indicating a hematogenous source of placental infection. Funisitis has been reported in leptospiral cases of abortion, and examination, both gross and histologic, of the umbilical cord should always be a part of every abortion investigation.⁵⁰ Serologic antibody conversion lasts for years, so serologic diagnoses are not helpful. Gross lesions are nonspecific. Diagnosis is best done by fluorescent antibody (FA) tests or Warthin-Starry (WS) silver stain of the allantochorion and umbilical cord. Demonstration of leptospirosis could aid in rapid diagnosis and have important clinical and therapeutic indications in the case of live-born, weak foals.⁵⁰

■ Treatment and Control Horses may shed spirochetes in urine for up to 90 days; therefore affected animals should be isolated and treated with antibiotics. Aborting mares should be isolated, and the stalls should be disinfected. Infected mares may be treated with streptomycin (10 mg/kg twice daily), penicillin (22,000 to 44,000 IU/kg IM twice daily), or oxytet­racycline (5 to 10 IV mg/kg) for a period of 1 week. Because L. pomona is the most common isolate in the United States, mares should be separated from other leptospiral hosts such as ruminants and pigs. A vaccine against L. pomona is available for horses. Vaccines for cattle are not effective in horses.

Protozoal Abortion

Pregnant mares with equine monocytic ehrlichiosis (Potomac horse fever), caused by the protozoa Neorickettsia risticii, may abort. Abortions caused by N. risticii have been documented in both natural and experimental cases.^51,52 Mares were infected at 90 to 180 days of gestation and aborted at around 217 days of gestation.

■ Clinical Signs and Diagnosis Abortions have been observed 2 to 3 months after clinical signs of ehrlichiosis.⁵³ Abortions were associated with placentitis and RFMs. Fetal histologic lesions include enterocolitis, periportal hepatitis, myocarditis, and lymphoid hyperplasia with necrosis of the mesenteric lymph nodes and spleen. Recovery of the protozoan may be from fetal bone marrow, spleen, lymph node, colon, or liver.^51,52 The diagnosis can be confirmed by identifying a small number of rickettsiae by PCR assay.

■ Treatment and Prevention Treatment with oxytet­racycline (6.6 mg/kg IV once daily) for 5 days in pregnant mares with clinical signs of ehrlichial colitis may prevent or reduce the incidence of abortion. Commercial vaccines against equine ehrlichiosis are available, but the protective effect of vaccines against abortion is unknown.

Neospora caninum is a known protozoal abortifacient in cattle. This protozoan has not been definitively shown to cause abortion in the mare, but its presence has been documented in aborted foals, suggesting the need for further investigation.⁵⁴

Insect-Related Abortion

In the equine breeding season of 2001, central Kentucky horses experienced pregnancy losses estimated to have affected more than 3000 mares (>60% of mares on some farms⁵⁵) and to have resulted in more than $330 million in losses.⁵⁶ The syndrome was named mare reproductive loss syndrome (MRLS). On a much smaller scale, MRLS was documented in mare abortions in north central Florida during the 2006 breeding season. Epi­demiologic studies noted abnormal weather patterns (sudden freezing in mid-April followed by unusually warm springtime temperatures) and positive correlations with the presence of black cherry trees (Prunus serotina) and abnormally large numbers of the eastern tent caterpillar (Malacosoma america- num).ⁱ⁵ Pregnancy loss was later linked to ingestion of the caterpillars themselves, with the toxic agent related to the larval exoskeleton.

■ Clinical Signs and Diagnosis Clinical signs preceding early embryonic death or abortion are typically not observed. Both early (40 to 150 days' gestation) and late (near-term) pregnancies are affected. Hyperechoic amniotic and allantoic fluids can be noted on ultrasonographic examination, along with a dead or dying fetus (slow heart rate, bgcolor=white>Pathology, virus isolation, fetal serology

splenomegaly, hepatopathy