Repeat Breeder
Bruce W. Christensen
Managing repeat breeders is often frustrating and expensive. The repeat breeder is an animal that has been bred during three or more successive heat periods without being diagnosed pregnant.47 An incidence of 10% to 15% repeat breeders is considered acceptable for dairies.48 The incidence increases with the herd size and the level of milk production and with the use of artificial insemination.48 This may be an even greater problem in the horse because pregnancy rates per cycle are normally between 60% and 70%, and 5% to 8% of mares lose their pregnancy in the first 4 months of gestation.49 The use of ultrasonography and embryo collection indicates that the incidence of early embryonic death (EED) in the mare is likely even higher.50 The syndrome of repeat breeders in mares is completely different from that in cows.
In mares it is often associated with persistent endometritis. This is discussed in detail in Chapter 43.The causes of repeat breeding are numerous and are related to male, female, and management factors (Boxes 12.8 and 12.9). The pathogenesis of repeat breeding involves either a failure of fertilization or EED.48 Some etiologies, such as heat stress in the herd, may involve both mechanisms. Fertilization rates are normal in heat-stressed cows that are bred artificially, but heat stress increases the rate of EED. Heat stress can cause failure of fertilization by affecting spermatogenesis in males used in a natural breeding program.51 When dealing with an individual repeat breeder, it is often wise to begin with the female. When several females are affected, the male should be eliminated as a source of the problem before proceeding. Management errors may be related to either male or female factors.
Fertilization failure is often the cause of repeat breeder syndrome.
Studies have demonstrated delayed or inadequate release of LH, as well as consequent delayed ovulation, in repeat breeder cows compared with those cows showing normal fertility rates.52 This observation has led to the investigation of GnRH (or its analogs) and prostaglandins as treatment options for repeat breeders, with some success.53,54 In addition to LH abnormalities, repeat breeder cows showed prolonged duration of estrus, prolonged lifespan of the preovulatory follicle, and a late postovulatory rise in progesterone.52 These changes negatively contribute to final oocyte maturation and competence in repeat breeder cows compared with unaffected cows.55 Insulin has been shown to be an important mediator of follicular development, steroidogenesis, oocyte maturation, and subsequent embryo development,56 and treatment with insulin has been shown to increase fertility in repeat breeder cows.57 Workers in Japan have linked the repeat breeder syndrome with abnormal profiles of endometrial epidermal growth factor (EGF). Assays of EGF have been suggested as diagnostic tools, and EGF treatment has been suggested to restore fertility.58,59Early embryonic death also contributes as a cause of infertility in repeat breeders.48,50 The interval between heats may help distinguish between EED and failure of fertilization. Failure of fertilization usually does not affect the interestrus interval. However, EED may prolong the interestrus interval if the fetal wastage occurs after the time of maternal recognition of pregnancy. Maternal recognition of pregnancy occurs at approximately days 15 to 17 after estrus in the cow, days 11 to 14 in the mare, and days 12 to 13 in the ewe.60 Animals experiencing EED after pregnancy recognition often have interestrus intervals corresponding to multiples of a normal cycle length. Luteal insufficiency is suspected to cause EED in some repeat breeder cows, and trials of exogenous progesterone supplementation have shown promise for maintaining pregnancy in young late-lactation repeat breeders.61
■ BOX 12.8
Causes of Repeat Breeding in Mares
Common Causes
Transition season Endometritis
Poor timing of artificial insemination Pneumovagina
Metritis
Endometrial fibrosis Poor heat detection Ovulation failure
Twins
Uterine lymphatic lacunae Endometrial cysts Early foal heat breed Poor uterine clearance
Ventral uterine sacculation
Less Common Causes
Diestrus breeding Urovagina
Rectovaginal fistula Malnutrition
Pyometra Heat stress
Poor semen quality Old age
Endophyte-infested fescue
Uncommon Causes
Salpingitis Hydrosalpinx Oviductal adhesions
Oophoritis Uterine neoplasia Cervical neoplasia Ovarian neoplasia Parovarian cysts
Contagious equine metritis Iodine deficiency
True hypothyroidism Phosphorus deficiency Zearalenone toxicity Intersexuality
Gonadal dysgenesis, sex reversal, trisomy Other karyotype abnormalities
Teratogenic factors Vitamin A deficiency Cervical trauma Luteal insufficiency
Approach to Diagnosis
Clinical differentiation of EED from failure of fertilization is difficult.
In addition to evaluation of heat detection and breeding techniques, it is important to obtain a detailed history. When dealing with a herd problem, the clinician begins by evaluating the male or males used or assessing the semen quality and techniques used for artificial insemination. When dealing with an individual repeat breeder, evaluation of the female is the first step.Evaluation of the male should include evaluation of the animal's physical condition, including the genitalia. The quality of the semen should be checked. The male's libido and ability to mount should be determined by observation or through historic information. Examination of the male for venereally transmitted diseases, such as trichomoniasis and campylobacteriosis in the bull and contagious equine metritis in the stallion, may be warranted if other factors are ruled out. When dealing with an artificial insemination program, the semen quality should be
| ■ BOX 12.9 | |
| Causes of Repeat Breeding in Ruminants | |
| Common Causes | Uncommon Causes |
| Heat detection | Johne's disease |
| Poor timing of artificial insemination | Tuberculosis |
| Inadequate or delayed luteinizing hormone surge | Vitamin A deficiency |
| Poor artificial insemination technique | Zinc deficiency |
| Malnutrition | Manganese deficiency |
| Follicular cysts | Cobalt deficiency |
| Endometritis | Copper deficiency |
| Heat stress | Molybdenum toxicity |
| Trichomoniasis | Selenium toxicity |
| Campylobacteriosis | Iodine deficiency |
| Leptospirosis | Iodine toxicity (B, O) |
| Inadequate uterine involution | Oophoritis Fat necrosis (B) |
| Less Common Causes | Brasilia, toxicity |
| Poor semen quality | Ovarian tumors |
| Inadequate male power (not enough males) | Progressive degenerative myeloencephalopathy of Brown Swiss |
| Infectious bovine rhinotracheitis (IBR) (B) | cattle (B) |
| Bovine virus diarrhea (BVD) (B) | Polybrominated biphenyl toxicity (B) |
| Bluetongue | Phytoestrogen toxicity (B, O) |
| Brucellosis | Hydrosalpinx |
| Anaplasmosis | Salpingitis |
| Toxoplasmosis (C, O) | Cervical anomalies and cysts |
| Border disease (C, O) | Chromosomal abnormalities (1/29 or 14/20 centric fusions) |
| Selenium deficiency | Fluoride toxicosis |
| Phosphorus deficiency | Segmental aplasia |
| Ureaplasmosis | Uridine monophosphate synthase deficiency |
| Urine pooling | Delayed ovulation |
| Pneumovagina, pneumouterus | Schistosomiasis (exotic) |
| Oviductal bursal adhesions | Tick-borne fever (exotic) |
| Segmental aplasia | Epivag (exotic) |
| Rectovaginal fistula | Leucaena Ieucocephala (exotic) |
| Parovarian cysts | Besnoitiosis (exotic) |
| Zearalenone toxicity (B, O) | Maedi, visna (exotic) |
| Fescue toxicity | Lumpy skin disease (exotic) |
| Uterine tumors Defective embryos Dietary protein toxicity | Onion grass toxicity (exotic) |
B, Bovine; C, caprine; O, ovine.
evaluated and the thawing, transporting, timing, and deposition techniques should be evaluated.
Errors in heat detection and the timing of breeding are major management causes of repeat breeding. Discussing and observing the methods used to determine when an animal should be bred are important in dealing with both the individual animal and the herd. Milk or serum progesterone determinations at the time of breeding have proved helpful in determining the accuracy of heat detection and timing of insemination. In some dairies 40% to 50% of the cows are bred at the wrong time.
Examination of the female or females should begin with evaluation of the body condition. Poor nutrition has been associated with repeat breeding.62 The reproductive examination should include evaluation of the vulva, vagina, cervix, uterus, oviducts, and ovaries. Poor vulvar conformation may lead to pneumovagina and endometritis, resulting in EED. The spermicidal effect of urine may cause failure of fertilization in the mare or cow that pools urine in the vagina. Cervical canal occlusion can prevent fertilization. An abnormal uterine environment may also lead to repeat breeding. Endometritis with minimal intraluminal pus may cause failure of fertilization but often results in EED. Unlike ruminants, the mare may continue to display estrus while experiencing pyometra. The volume of pus present in the uterus will cause failure of fertilization. Hydrosalpinx or salpingitis may lead to failure of fertilization by blocking sperm or ovum passage. Ovulation abnormalities such as delayed ovulation or ovarian cyst formation may result in failure of fertilization. Whenever possible, including a uterine culture, cytologic smear, and endometrial biopsy as part of the examination is likely to help determine the cause of the infertility.
Differentiation of EED from failure of fertilization in repeat breeders has been facilitated by the use of embryo flushing techniques and ultrasonography. Collection of unfertilized ova indicates failure of fertilization; collection of degenerating embryos indicates early embryonic death.
In ruminants, failure to collect ova or embryos may indicate oviductal blockage resulting in failure of fertilization. This is not the case for mares because they usually retain unfertilized ova in the oviducts.Ultrasonic determination of pregnancy in the mare and cow has made early detection of pregnancy possible. Loss of an embryo after detecting it with ultrasound at 10 days of gestation confirms EED. Pregnancy wastage can be confirmed later in gestation with sequential rectal palpations of the reproductive tract or ultrasonic evaluation. Hormone assays are also helpful for confirming embryo or fetal loss.
An assay for eCG, previously called pregnant mare serum gonadotropin (PMSG), can be used to determine if a mare was pregnant long enough to stimulate formation of the endometrial cups and eCG production. eCG can be detected at about 40 days of gestation with these kits. The endometrial cups continue to produce eCG until 120 to 150 days of gestation even if the fetus dies. Therefore eCG can be used to confirm EED but not failure of fertilization. Progesterone determination cannot be used to confirm pregnancy in the mare or ruminants. However, it can be used to confirm nonpregnancy if the progesterone level is low early in the expected gestation. A bovine early conception factor test can be used to confirm fertilization, but it does not rule out EED later.
The fetally derived hormone-metabolite estrone sulfate has been used to determine the presence of a live fetus. It is detectable in the serum or urine of the dam if the fetus is alive after 45 days of gestation in the doe, 70 days of gestation in the ewe, 100 days of gestation in the mare, and 120 days of gestation in the cow.63,64 Thus a decline in estrone sulfate indicates death of the fetus. Estrone sulfate is probably most helpful in confirming fetal loss in the doe and ewe because other techniques are available in the larger species.
Boxes 12.8 and 12.9 list the causes of repeat breeding in mares and ruminants. The causes have been divided into expected frequencies of occurrence.