Female Reproductive Disorders

Bruce W. Christensen • Bret R. McNabb • Mats H.T. Troedsson • Elizabeth M. Woodward

Nonpathogenic Infertility

Breeding Season

Mares

The mare is a seasonally polyestrous animal, breeding during seasons of long day length.

■ Clinical Signs During the breeding season, mares ovulate every 21 days (range 19 to 22 days).¹ Estrus (5 to 7 days but variable) is characterized by the presence of an ovarian follicle, serum progesterone level of less than 1 ng/mL, and sexual receptivity. During estrus the cervix is palpably relaxed and the uterus is edematous. One or two follicular waves occur per cycle, and preovulatory follicles are 45 to 60 mm in diameter, often with a cone-shaped appearance on ultrasonography.² Ovulation occurs 24 to 48 hours before the end of estrus and may be accompanied by ovarian sensitivity.¹ The ruptured follicle is replaced by a corpus luteum (CL). Diestrus (luteal phase) is predictable in length because regression of the CL, caused by release of endometrial prostaglandin F_2α (PGF_2α), occurs 14 to 15 days after ovulation.³ During diestrus and early pregnancy the cervix is tight and the uterus has increased tone. Diestrous ovulations occur and may be fertile.⁴ First postpartum estrus (“foal heat”) begins in the week after foaling, and ovula­tion occurs in most mares 7 to 15 days postpartum.

Ruminants

cows. Cows are polyestrous, but seasonal differences in fertility may be caused by climate. The estrous cycle averages 21 days (range 17 to 25 days), and the duration of estrus averages 12 to 16 hours (range 6 to 24 hours).

In the absence of a bull, estrus can be detected in cows by their homosexual (bisexual) activity. Cows that stand to be mounted by another cow are in estrus (standing heat). Secondary signs that may be helpful in detecting estrus include restlessness and increased activity, vulvar hyperemia and edema, and a clear mucous discharge. Errors in heat detection are a common cause of infertility on large dairy farms.⁶ The optimum time for insemination of cows is between 16 and 24 hours after the onset of estrus. Insemination of cows based on standing to be mounted results in a higher pregnancy rate than if it is based on secondary signs of estrus. Well-managed dairy cows with uncomplicated periparturient experiences may ovulate approxi­mately 20 to 25 days after calving, whereas beef cows with nursing calves usually do not ovulate until 40 or more days after calving. The presence of the calf appears to be responsible for the difference in return to cyclicity.⁷

SHEEP. Coarse-wooled breeds of ewes are seasonally polyestrous during the autumn and winter (short photoperiod) in temperate climates. Ovulation can be induced in seasonally anestrous ewes by artificial simulation of day length and temperatures characteristic of autumn (reduced photoperiod and reduced ambient temperature), but the long latency period required for response to manipulation of light and temperature makes the procedure impractical. Ewes of fine-wooled breeds may be polyestrous throughout the year if adequately nourished. The estrous cycle of ewes averages 17 days (range 14 to 19 days), and the duration of estrus averages 36 hours. Ovulation occurs spontaneously 24 hours after the onset of estrus. Ewes display few, if any, signs of estrus unless a male is present. The primary signs of estrus include seeking the ram and standing for mating.

goats. Does in temperate climates are seasonally polyes­trous from late summer until early spring (short photoperiod). Onset of the breeding season in yearling does can be advanced by exposing them to 19 hours of artificial light per day for 70 days beginning in mid to late winter. Termination of artificial light results in a relative decrease in day length and stimulation of estrus and ovulation.⁸ Alternatively, the breeding season may be hastened by exposing does to 14 to 18 hours of light per day for 3 months, followed by a reduction to 6 hours of light per day. The estrous cycle averages 21 days, and estrus lasts 18 to 36 hours. Ovulation occurs spontaneously 24 hours after the onset of estrus. An intact male or male pheromone is usually necessary for estrus detection. The primary signs of estrus are seeking the buck and standing for service. Secondary signs of estrus in does include rapid tail switching, restlessness, increased frequency of urination and vocalization, transient decrease in appetite and milk production, and edema and hyperemia of the vulva. As in sheep, parturition takes place during the anestrous season, and return to cyclicity in does is delayed until the next breeding season.⁸

CAMELIDS. South American camelids bred in North America are nonseasonal. In keeping with management decisions, they are often bred in a seasonal manner to avoid having newborn crias during the hottest or coldest months of the year. Some consider the South American camelids to be polyestrous, whereas others argue that they do not have a true estrous cycle.⁹ These discrepancies arise from the fact that camelids are induced ovulators. Cyclic ovarian activity (e.g., transition from estrus to diestrus) is caused by coital activity.

■ Clinical Signs and Diagnosis Approximately 70% to 80% of cows affected by CFD are anestrus, whereas 20% to 30% display frequent or intense estrus (nymphomania). Cystic ovarian disease affects 10% to 30% of dairy cows. The condition is rare in commercial beef cows because of rigid culling for reproductive failure.

The physical appearance of cows with CFD depends on the duration of the condition. No changes are apparent after a short time, but in long-standing cases relaxation of the pelvic ligaments may result in prominence of the tailhead and masculine characteristics such as a crested neck.

The diagnosis of CFD is based on an accurate history and clinical examination. A history of constant or frequent estrus, short interestrous intervals, or anestrus may suggest CFD. Examination of the ovaries by palpation per rectum reveals the presence of enlarged fluid-filled structures raised above the surface of the ovary that greatly increase total ovarian size. Ovarian cysts are larger (>25 mm) than preovulatory follicles (15 to 25 mm). Differentiation between a single large cyst and several smaller cysts on the same ovary may require ultraso­nographic examination, as does recognition of the presence of partially luteinized cysts (based on peripheral progesterone concentrations).

During palpation of the ovaries, several normal structures may complicate the diagnosis of CFD. Normal preovulatory follicles may approach 25 mm in diameter and have palpable characteristics similar to those of small cysts. During the follicular phase of the estrous cycle, however, the uterus responds to palpation by becoming more turgid, whereas the uterus of a cow with CFD is typically flaccid and unresponsive. In neglected cases of CFD, mucometra may develop and must be differentiated from pregnancy. During the first 5 to 7 days of the estrous cycle, the developing CL may be smooth and soft and is commonly mistaken for an ovarian cyst. More mature CLs are solid and liver-like in consistency, often feature a palpable ovulatory papilla at the apex, and are more easily differentiated from ovarian cysts. However, 10% to 20% of mature CLs may lack an ovulatory papilla, making them more easily confused with ovarian cysts. Ultrasonography is generally more accurate in identifying subtle structural differences than transrectal palpation. Salpingitis, hydrosalpinx, oophoritis, ovarian abscesses, ovarian neoplasms, and cysts of the fimbria are other causes of enlargement of the ovary and surrounding structures that must be differentiated from ovarian cysts.³

Histories that may erroneously suggest CFD include appar­ently short interestrous intervals because of inaccurate detection of estrus. Oxytocin administered to stimulate milk letdown may result in short interestrous intervals that may spuriously be suggestive of CFD. The estrous cycle may be shortened by approximately 1 week by administering 100 IU of oxytocin per day on days 2 through 6⁴ or on days 3 through 7 or 8.5

■ Clinical Pathology Plasma progesterone concentrations are low in cows with follicular cysts.

■ Treatment and Prognosis The goal in treating CFD is to induce luteinization of the cyst and reestablish normal estrous cycles. Several methods have been recommended.

SPONTANEOUS RECOVERY. Spontaneous recovery from CFD occurs in up to 60% of cows that develop CFD before the first ovulation after calving but in only approximately 20% of cases that develop after the first postpartum ovulation. Evaluation of therapeutic agents for CFD may be confounded by spontaneous recovery.

LUTEINIZING HORMONE. Recommended doses of human chorionic gonadotropin (hCG) range from 5000IU either intravenously (IV) or intramuscularly (IM) to 10,000 IU IM. Among cows treated with a single dose of hCG, 65% to 80% establish a normal estrous cycle within 3 to 4 weeks; a second or third dose may be required in cows that do not respond after 3 to 4 weeks or in cases in which nymphomania persists. Anaphylaxis after repeated treatments with a larger protein hormone such as hCG can occur. Antibodies to hCG may reduce the effectiveness of sequential treatments. Therapeutic response to follicular cysts, both endocrinologically and clinically, is essentially equivalent between hCG and gonadotropin-releasing hormone (GnRH).

GONADOTROPIN-RELEASING HORMONE. Currently the most common treatment for ovarian cysts, especially follicular cysts, is an injection of GnRH (100 μg IM). Cows that respond to this treatment have an average interval to estrus of one estrous cycle or 18 to 24 days. The treatment to breeding interval can be shortened by administering GnRH at the time of diagnosis, followed by a luteolytic dose of prostaglandin 10 days to 2 weeks later. With this regimen, it is not critical whether the cyst is follicular or luteal or even whether it is a misdiagnosed large, smooth CL with or without a fluid-filled central cavity. Most veterinarians agree that accurate differential diagnosis by rectal palpation among follicular cysts, luteal cysts, and some CLs can be a problem.

PROSTAGLANDIN F_2α. Luteal cysts can be treated with the luteolytic activity of PGF_2α. The advantages are the quicker return to estrus for those cows able to respond and the lower cost of PGF_2α. Cysts that luteinize in response to GnRH regress at a time similar to that of normal CLs. Treatment with PGF_2α may be used to reduce the interval from treatment with GnRH to estrus from 18 to 24 days to an average of 12 to 14 days by administering PGF_2α at 9 days after GnRH. Most clinicians are only approximately 50% accurate in determining the degree of luteinization of cysts by palpation per rectum; therefore measurement of concentrations of progesterone in milk or of plasma from affected cows allows the selection of GnRH or hCG for treatment of follicular cysts and PGF_2α for the treat­ment of luteinized cysts. Ultrasonography can also be used to make an accurate diagnosis.⁶

MANUAL RUPTURE. Thin-walled follicular cysts may be ruptured inadvertently during examination of the ovaries, and some practitioners intentionally may attempt cyst rupture. Recovery rates after manual rupture have rarely been studied in well-designed controlled experiments but are generally within the range reported for spontaneous recovery. Deliberate manual rupture of ovarian cysts is considered an obsolete form of treatment by some veterinary clinicians, but others routinely use the procedure—especially as an initial treatment for cysts found during the voluntary waiting period. Manual rupture of cysts may be followed by hemorrhage and adhesions between the ovary and surrounding structures. These complications appear to be much more common with the use of digital pressure to enucleate CLs (also no longer performed) than with manual rupture of ovarian cysts.

Ewes and Does

Cystic ovaries appear to be more common in goats than in sheep. In one study 12% of goats had cystic ovaries when examined at a slaughterhouse.⁷ The condition is often over­diagnosed by owners observing nymphomania or abnormal cyclicity. Treatment typically consists of administering exogenous ovulation-hastening drugs (hCG and GnRH).⁸ LH surge is noted usually within 2 hours of GnRH administration. Ten days later, PGF_2α may be administered to bring the doe into heat (roughly 2 to 2.5 days after administration).

Camelids

Hemorrhagic follicles are observed in nonbred llamas and usually regress within 22 days.⁹ Follicles larger than 12 mm are considered by some authors as pathologic cysts. These structures may, however, be anovulatory follicles. They may have a negative influence on the emergence of other follicular waves, but this influence seems to last for only approximately 8 days.¹⁰

Poor Nutrition

As with other species, poor body condition, depressed energy intake, and decreased vitamin and mineral intake suppress reproductive activity in ewes and does. Lowered energy balance results in poor or weak signs of estrus, depressed ovulation, abnormal cycle, and delayed puberty. Deficiencies in energy, protein, vitamins A and E, phosphorus, and many trace minerals (iodine, copper) are commonly seen. These deficiencies are most commonly associated with irregular estrous cycles.

Ovarian Reserve and Anti-Mullerian Hormone

The mammalian ovarian reserve declines with age, and antral follicle count (AFC) is thought to be predictive of ovarian reserve and fertility.¹ Plasma levels of anti-mullerian hormone (AMH) have been directly correlated with AFC in multiple species, including mares.^2,3 Based on these findings, AMH has been suggested as a promising indicator of ovarian reserve (and therefore “reproductive age”).^4,5 In the female, AMH is produced by granulosa cells in developing follicles and serves in the regulation of primordial follicular recruit­ment and development into primary follicles, preserving the ovarian reserve.^6-8 The mechanisms for the role of AMH in folliculogenesis are still being understood; however, it has been demonstrated that AMH restricts follicular development by decreasing the sensitivity to follicle stimulating hormone (FSH) in granulosa cells.^9,10 Finally, perhaps the more commonly known clinical application of AMH in mare reproductive health is as a reliable marker for the presence of granulosa cell tumors.¹¹

Plant Toxicity

Ergot Alkaloids

The consumption of fescue infected with Neotyphodium coeno- phialum is associated with decreased reproductive efficiency (see Chapter 12). The ergot alkaloids have been shown to affect prolactin production in ewes and to increase the interval from introduction of the ram to conception.

Estrogen-Producing Plants

Sheep appear to be sensitive to the effects of phytoestrogens. Clinical observations include infertility, irregular and prolonged heat cycles, lowered conception rates, and early embryonic death.

Heat Stress

Fertility in lactating cows is decreased during the hot seasons of the year. Heat stress may cause decreased estrus detection, impair follicular development, disrupt function of the reproductive tract, affect oocyte competence, and lead to early embryonic death. Embryos develop resistance to heat shock as they age. Bovine morulae to blastocyst stages are unaffected by heat shock.¹

Anestrus

The causes of anestrus are multiple and include diseases of the reproductive and other systems. In addition, the problem is complicated by management factors that cause estrus to pass undetected, even though the animal's estrous cycles and estrous behavior are normal. Common causes of anestrus in mares are summarized in Table 43.1.

Mares

Puberty

The mare likely undergoes puberty between the ages of 12 and 24 months. Because the horse is not an agricultural produc­tion animal, there has been little interest in studying the onset of puberty as in other species, where hastening puberty increases production. Most mares are not bred until they are at least 3 years old, thus making prepubertal status an unlikely differential diagnosis for infertility.

Seasonal Anestrus

■ Clinical Signs and Diagnosis The mare is a seasonally polyestrous animal, showing anestrus during the shorter days of the year and cycling regularly during the longer days. Length of anestrus varies from one to several months, although some mares, particularly in the tropics, may cycle year-round.¹ In California, Australia, and South Africa 18% to 25% of mares cycle year-round.^2-4 Anestrous mares may be indifferent to teasing and do not show regular estrous behavior. Ovaries are small and firm on palpation, and the uterus is flaccid with a thin endometrium. The cervix has mild tone and may be indistinct. On speculum examination of the vagina, the vaginal mucosa is pale and dry, and the cervix usually appears closed but is occasionally open or may be easily opened. Mares that experience seasonal anestrus will go through a transition period in late winter and early spring, characterized by the develop­ment of waves of antral follicles that regress without ovulation because the ovulatory surge of LH is absent.⁵ Transitional mares exhibit signs of estrus, including clitoral “winking,” tail flagging, and urinating in the presence of the stallion. Eventually, increasing LH concentration coincides with a large follicle, resulting in ovulation. After the first ovulation of the season, the mare will continue to ovulate on successive estrous cycles. A transition period is also observed during the fall as the mare changes from a polyestrous condition to the winter anestrus. Differential diagnoses for seasonal anestrus are listed in Table 43.1.

■ Treatment and Prognosis As day length increases, most mares ovulate and begin regular cyclicity without treat­ment. Methods to advance the onset of regular ovulatory periods can be both managerial and pharmacologic and are discussed in the following sections.

ARTIFICIAL LIGHTING. The vernal transition can be moved but not shortened beyond its physiologic length of 6 to 8 weeks by exposure of mares to artificial light. A common artificial lighting regimen is to expose the mares to 16 hours of light and 8 hours of dark by extending the photoperiod in the evening starting in late November to initiate ovulation by February (in the northern hemisphere). Light should be added to the end of the day, or split between the beginning and end of the day, as opposed to adding light only at the beginning of the day.⁶ An alternative regimen is to expose mares to 1 hour of artificial light 9.5 to 10.5 hours after the onset of darkness.⁷ Use of one 200-watt incandescent bulb or two 40-watt fluorescent tubes at a height of 7 to 8 feet in a 12- ? 12-foot box stall has been recommended.⁸ Paddock lighting has been described.

Recently, research has evaluated the effectiveness of a mask fitted with a single low-intensity blue light as a method to induce the onset of cycling.⁸ The masks were compared with mares not under lights and with mares stalled under lights using a conventional protocol. The study found that the masks were able to achieve the same results as the traditional protocol, bringing mares out of seasonal anestrous earlier than the control group.

EXPOSURE TO STALLIONS AND SOCIAL ENVIRON­MENT. Alterations in social environment can alter the timing of ovulation in several species. Recent work has investigated social factors and the cessation of seasonal anestrus in mares. The group found that anestrus mares exposed to a stallion several times per week ovulated earlier and more frequently than anestrus mares never exposed to stallions.⁹

GONADOTROPIN-RELEASING HORMONE. Treatment with GnRH or a GnRH analog for mares in anestrus or spring transition has been shown to induce ovulation.^10-15 Twice-daily injections of a GnRH agonist induced ovulation in a majority of mares within 2 to 3 weeks.¹⁴ Mares that are in deep anestrus (January and February, northern hemisphere) can be expected to return to anestrus after treatment.

DOPAMINE ANTAGONISTS. Domperidone and sulpiride have been reported to stimulate follicular activity and advance the first ovulation of the year in seasonally anestrous mares.¹⁶ However, the efficacy of dopamine antagonists in advancing follicular growth and ovulation in anestrous mares has been questioned recently, and it has been suggested that adjustments in light and climatic conditions may influence the efficacy of the treatment.^17,18

STEROIDS. Exogenous progestins suppress the release of LH from the anterior pituitary and may be used for estrous regulation during the vernal transition. After treatment of mares for 10 to 14 days, withdrawal of progestin may result in LH release from the pituitary and estrus beginning in 4 to 5 days, with ovulation within 10 days after cessation of treatment. Mares should be in mid to late transition and have a follicle at least 25 mm in size to respond to treatment. Progestins will not induce estrus or ovulation in anestrous mares.¹⁹ The recom­mended dose of progesterone in oil is 150 to 300 mg daily by IM injection. The synthetic progestin altrenogest is administered orally (PO) at 0.044 mg/kg daily. Progestins may be used in combination with extended photoperiod and gonadotropins. Products that are ineffective or unavailable include repositol progesterone, melengestrol acetate, chlormadinone acetate, proligestone, medroxyprogesterone acetate, hydroxyproges­terone acetate, and norgestomet implants.

Synchronization of the first ovulation (or any ovulation during the cyclic season) can be accomplished by the administra­tion of a combination of progesterone in oil (150 mg/day IM) and estradiol-17β (10 mg/day IM) once daily for 10 days.²⁰ Treatment is most effective if given after mares have been under lights for 45 to 60 days. PGF_2α should be given on the last day of steroid treatment. Treated mares will ovulate within 8 to 10 days after the last treatment.

GONADOTROPINS. At a dose of 2500 to 3000 IU, hCG may induce ovulation within 48 hours when administered to a mare with a follicle larger than 35 mm in diameter²¹ and may reduce time to first ovulation in transitional mares, particularly when used in combination with lights and/or progesterone treatment. Ovulation response here is less predict­able than that induced with hCG during the breeding season.

Based on a recent study, treatment of seasonally anestrous mares with recombinant equine FSH (reFSH) is effective in stimulating development of follicles and advancing the first ovulation of the year.²² Treatment with FSH resulted in multiple ovulations but was not successful in inducing continued cyclicity.

■ TABLE 43.1

Differential Diagnosis of Anestrus in Mares

AMH, Anti-mullerian hormone; PGF2α, prostaglandin F2₀..

FOLLICULAR ASPIRATION. Ultrasound-guided transvaginal follicular aspiration of follicles less than 35 mm in diameter has been shown to hasten the onset of cyclicity in transitional mares.²³ Follicular aspiration resulted in the formation of an active CL, and subsequent treatment with PGF₂₀ resulted in estrous behavior and ovulation of a dominant follicle.

Prolonged Luteal Phase and Pseudopregnancy

Mares that experience embryonic loss in the presence of endometrial cups (days 35 to 150 of gestation) are said to be pseudopregnant (pseudopregnancy may also refer to the condition in which a conceptus was lost after maternal recognition of pregnancy and before the development of endometrial cups, resulting in prolonged luteal life). Despite the loss of the fetus and placental tissue, endometrial cups remain in place and continue to secrete equine chorionic gonadotropin (eCG) for a similar period to that in a pregnant mare, to 100 to 150 days of gestation.²⁴ The primary and secondary CLs may regress after embryonic loss, allowing the mare to return to cyclicity,^25,26 or remain during eCG secretion, maintaining high levels of peripheral progesterone and preventing the mare from cycling. Persistent endometrial cups throughout pregnancy and during the following breeding season have been described.²⁷

■ Treatment and Prognosis In untreated mares, cyclic activity is often reestablished after the cessation of eCG secre­tion. Repeated daily injections of PGF₂₀ products have been reported to cause luteal regression in pseudopregnant mares,²⁸ but only CLs older than 5 days respond to the treatment, which may prevent mares returning to estrus. Pregnancies have occurred in the face of high eCG,²9 but fertility of treated mares is usually low.

Lack of Behavioral Estrus (Silent Estrus)

Behavioral estrus may not be detected in otherwise normal mares as a result of inadequate estrus detection or a failure on the part of the mare to show obvious signs of estrus. The latter may occur in up to 15% of mares on well-managed farms.¹ Inadequate estrus detection may result from human apathy or ignorance or from use of a low-libido or inexperienced stallion. Teasing mares as a group may make detection of estrus more difficult, especially for nervous mares, mares with foals, and mares of low social rank. Use of anabolic steroids may suppress behavioral estrus.

■ Clinical Signs and Diagnosis The mare fails to show estrus on adequate teasing with a stallion. Differential diagnoses are listed in Table 43.2.

■ Treatment and Prognosis Management should be examined to ensure a competent teasing routine. When approached by a stallion, mares in estrus stand still with ears held forward; they may elevate the tail, rhythmically evert the clitoris (“winking”), assume a squatting posture, urinate, and lean against the teasing chute toward the stallion. Mares that are in diestrus move about and hold their ears back; they may strike, kick, squeal, swish their tails, and forcefully void small amounts of urine. Experienced personnel should handle both stallion and mare. The teaser stallion should have adequate libido without being aggressive. Transrectal palpation and ultrasonography should supplement teasing. Some mares are indifferent to teasing, and records of sequential palpation must be relied on for breeding. Progesterone concentrations of less than 1 ng/mL are consistent with estrus but may also occur in anestrous mares. Mares that fail to show behavioral estrus should be bred by artificial insemination (AI) if allowed by the breed register or with appropriate restraint used for natural cover.

Behavioral Nymphomania

Abnormal estrous behavior and aggression may be demonstrated by otherwise normal mares at any stage of the estrous cycle. Ovarian tumors should be considered as an important dif­ferential diagnosis.¹

■ Clinical Signs and Diagnosis Exaggerated signs of estrus occur, initially during estrus and then throughout the cycle. Mares may develop behavioral anomalies and become aggressive. Differential diagnoses are listed in Table 43.2. It is important to differentiate abnormal estrous behavior from unrelated systemic or behavioral problems.²

■ Treatment and Prognosis Exogenous progestins have been used to limited effect. Short-term dexamethasone treat­ment (5 to 10 mg) may alleviate signs for 3 to 4 days. The prognosis for resolution after bilateral ovariectomy is unpredict­able, as it may be successful in some cases and exacerbate the undesired behaviors in others.³

Ruminants

Common causes of anestrus in cows are summarized in Table 43.3.

Unobserved or Silent Estrus

Cow

Failure of a cow to display, or a manager to observe, the signs of estrus contributes significantly to reproductive inefficiency. When the presenting history suggests anestrus (failure to have a normal estrous cycle), the clinician must determine if the cause is failure of the manager to detect estrus in normal cows or failure of the cow to cycle because of some abnormal process. In dairy herds approximately 90% of cows presented for examination because of a history of anestrus have evidence of normal cyclic ovarian changes, whereas only approximately 10% are affected by an abnormality that suspends the estrous cycle (i.e., only ≈10% are in true anestrus).

Nearly 90% of well-managed dairy cows have initiated normal-length estrous cycles by 60 days after calving, but only approximately 60% are detected correctly to be in estrus by that time.¹ Rates of estrus detection by twice-daily observation range from 50% to 73% depending on the skill of the observer.

Mounting activity and estrous behavior are reduced by hot and cold ambient temperatures and during the times of milking and feeding. More mounts are observed when cows are kept on dirt than on concrete. Estrous behavior varies with the time of day and may be an inverse reflection of extraneous activity interfering with cow behavior. In one study, 43% of cows showed heat between midnight and 6 AM; 22% between 6 AM and noon; 10% between noon and 6 PM; and 25% between 6 PM and midnight.²

■ TABLE 43.3

Differential Diagnosis of Anestrus in Cows

GnRH, Gonadotropin-releasing hormone; hCG, human chorionic gonadotropin; PGF2α, prostaglandin F2₀..

Estrus in dairy cows averages 7 to 16 hours but ranges from 0.5 to 36 hours. Sixty-five percent of cows are in estrus for less than 16 hours, and 25% are in estrus for less than 8 hours.³ The number of mounts per hour ranges from 2 to 8, and the total number of mounts during estrus ranges from 11 to 56. Total number of mounts per estrus increases with the number of cows simultaneously in estrus.

■ Clinical Signs and Diagnosis Dairy herds in which infertility is caused by inaccurate estrus detection are usually characterized by prolonged intervals from calving to first breeding and between services; insemination intervals of 10 to 15 days and 30 to 35 days; records of examinations that confirm cyclic ovarian changes but in which observation of estrus is not recorded; and finding more than 15% of cows presented for pregnancy examination to be nonpregnant. Insemination during the luteal phase of the estrous cycle may occur in 10% to 20% of cows and is not likely to result in conception; insemination of pregnant cows may be followed by abortion.

The diagnosis of unobserved estrus requires sequential examination of affected cows and accurate records. Other causes of anestrus are eliminated. Conditions such as cystic follicles, pyometra, mummified fetuses, granulosa-theca cell tumors, and segmental aplasia that cause anestrus affect individual animals. Anestrus caused by undernutrition is characterized by depressed milk production and low body condition score.

■ Treatment and Prognosis PGF_2α is widely used in clinical management of unobserved estrus. Mature CLs (≈day 6 through day 18 of the estrous cycle) are responsive to PGF_2α-induced luteolysis. Estrus occurs an average of 3 days (range 2 to 5 days) after administration of PGF_2α, depending on the follicular status of the ovaries at the time of injection. The endocrine events surrounding the controlled estrus are indistinguishable from those surrounding spontaneous estrus and ovulation. Treatment with PGF_2α shortens the intervals from treatment to first breeding and from treatment to concep­tion but has no effect on fertility. The benefits of PGF_2α treatment are limited by inaccurate palpation of the temporary ovarian structures, injection during the wrong phase of the cycle, and failure of the manager to observe estrus in treated cows (timed AI can be used to overcome this problem).

Measurement of progesterone concentrations in milk samples taken on the day of breeding is useful in herds with a history of reduced fertility to confirm that cows being inseminated are not in the luteal phase of the estrous cycle. If more than an occasional cow presented for insemination has an elevated concentration of progesterone, the methods of estrus detection should be reviewed. Enzyme immunoassay kits for measuring concentrations of progesterone in milk and plasma of cows and other female animals have been described and are com­mercially available.

Various heat detection aids have been developed. Several of these use devices mounted on the tailhead that record when a cow has stood to be ridden. Pressure-sensitive devices that are glued to the tailhead and change color after sustained pressure by the weight of a mounting cow are commonly used. Similarly, pressure-sensitive devices glued to the tailhead can send a record of riding events directly to a computer. Chalk, cattle crayon marker, or paint applied to the tailhead are inexpensive aids that rub off when the animal is mounted when she is in heat. These methods require daily maintenance and twice-daily evaluation to function effectively. Detection aids that measure changes in activity (pedometers), mucous con­ductivity, or body temperature can be used successfully. Accuracy is enhanced when measurements are related to previous estrous activity and progesterone concentrations.⁴

■ Prevention and Control Because unobserved estrus is primarily a problem of management, efforts to reduce time lost from delayed breeding are directed at improving efficiency of heat detection. Accurate records are required to identify cows that have not been observed in estrus by 40 days after calving. Cows not observed in estrus by 40 days after calving should be examined, and abnormalities of the reproductive organs that cause anestrus treated as indicated. The time of estrus can be predicted by palpation of the temporary ovarian structures, or estrus can be controlled with PGF_2α. The most significant benefit of a planned herd health program is stimula­tion of improvements in management that decrease the interval from calving to conception as a result of improved estrus detection.

Anestrus after insemination is frequently interpreted as a clinical sign of pregnancy. However, unobserved estrus in cows that have failed to conceive or have experienced early embryonic death (postservice anestrus) contributes significantly to increased calving intervals. Clinical management of postservice anestrus depends on diligent observation of cows 18 to 24 days after breeding and identification of nonpregnant cows as early as possible after the infertile service so that they may be rein­seminated with minimum delay. Nonpregnant cows may be accurately identified by ovarian palpation or ultrasonography for absence of a mature CL, by low milk or plasma progesterone at the time of the first expected postservice estrus (≈21 days after breeding), or by palpation of the uterus per rectum before the second expected postservice estrus (30 to 42 days after breeding). Biochemical markers for pregnancy, such as pregnancy-associated glycoproteins (including pregnancy­specific protein B), have been validated as early as 28 days post insemination with a sensitivity and specificity of 93.9% and 95.5%, respectively.⁵

Ewe

The breeding season of most breeds of sheep maintained at temperate latitudes is restricted to late summer, autumn, and early winter, although some breeds cycle all year long. There is almost no homosexual interaction among ewes; therefore a male must be present to stimulate display of estrus.

Introduction of a ram (either intact or vasectomized) into a flock of ewes advances the breeding season. Most ewes ovulate by 3 to 6 days after introduction of rams. The induced ovulation is seldom accompanied by estrus, but the subsequent estrus approximately 17 days later is ovulatory and fertile. The “ram effect” is lost when rams are allowed to associate with ewes throughout the year.

Return to estrus after mating may be detected in a flock of ewes by fitting the ram with a brisket device that marks serviced ewes. Return of an excessive number of ewes to service after breeding alerts the owner to the possibility of infertility.

AI of ewes is rare in the United States but more popular in other countries. Laparoscopic AI is required due to the tortuous nature of the ewe's cervix and therefore is a more complicated procedure than in other species. Detection of estrus for AI depends on the use of teaser rams mingled with the ewes or led through the flock several times daily.

Doe

The breeding season of does is similar to that of ewes (i.e., it surrounds the autumnal equinox). During periods of short daylight, the normal estrous cycle of does is 20 to 21 days. Homosexual interaction among estrous does rarely occurs, so signs of estrus must be elicited by teasing. Signs of estrus may also be evoked by exposure to male pheromones by way of a “buck jar” prepared by rubbing a cloth over the scent glands caudomedial to the horns of a mature buck during the breeding season and storing the cloth in a tightly closed container. If estrus is not observed in does exposed to a mature buck or to a buck jar during the physiologic breeding season, pregnancy or pseudopregnancy might be considered as possible causes of anestrus. Severely parasitized or inadequately nourished does do not have normal estrous cycles. Deficiencies of phosphorus, iodine, and manganese have been suggested as causes of anestrus in does.

Introduction of bucks into a flock of does early in the breeding season results in initiation of estrous cycles and some degree of synchrony of estrus approximately 10 days after introduction of the bucks. In contrast to ewes, however, the first ovulation after exposure to males is accompanied by estrus and fertile mating.

Camelids

Most female South American camelids, although showing signs of ovarian cyclicity as early as 5 months of age, have decreased fertility until approximately 15 months of age. A female camelid should be at least 60% of her expected adult weight before she is bred. Male camelids have a preputial attachment of the penis that is not separated until 2 to 3 years of age. However, some males may detach as early as 15 months of age. Before this time they will show mounting behavior but will not be capable of intromission.