Volume 48 | Issue 1 Article 4 1986 Infertility in the Mare Mary A. Ebert Iowa State University Richard L. Riese Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/iowastate_veterinarian Part of the Female Urogenital Diseases and Pregnancy Complications Commons, and the Large or Food Animal and Equine Medicine Commons Recommended Citation Ebert, Mary A. and Riese, Richard L. (1986) "Infertility in the Mare," Iowa State University Veterinarian: Vol. 48 : Iss. 1 , Article 4. Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol48/iss1/4 This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Iowa State University Veterinarian by an authorized editor of Iowa State University Digital Repository. For more information, please contact [email protected]. Infertility in the Mare Mary A. Ebert, BS, DVM,* Richard L. Riese, DVM, DACT* * INTRODUCTION uterine defense system, in addition to the leu­ Infertility in the mare results in a signifi­ kocyte function, includes ovarian hormones, cant loss of dollars in the horse industry every non-cellular bactericidal factors, and immune year. It is defined as the absence of the ability responses.28 Local synthesis of antibodies, to conceive. 13 There are many causes of infer­ mainly IgA, occurs in the secrectory epithe­ tility that are recognized, including infectious, lium, and a transport mechanism moves the inflammatory, a faulty uterine immune sys­ polymeric Ig across into the uterus, cervix, tem, trauma and scarring, hormonal, twin­ and vagina.32 Six of the ten known equine ning, neoplasia, and congenital abnormali­ immunoglobulins have been found in uterine ties. flushings. Some investigators report that these are in higher concentrations in fertile mares, CAUSES OF INFERTILITY while others dispute these findings. 25 ,27 When Infectious endometritis is probably the bacteria penetrate the mucosal barrier, the number one cause of infertility in the mare, higher protein level stimulates the defense 6 25 and contributes significantly to fetal death. ,9 mechanism: ,27 Mares with a decreased re­ A large variety of organisms have been sistance to infection undergo rapid comple­ cultured in both the mare and stallion, but ment inactivation, possibly of enzymatic ori­ much disagreement exists as to the clinical gin. 1 A failure of the uterine defense significance of these positive cultures. 6 A large mechanism leads to a prolonged inflammation number of bacteria normally enter the uterus and an endometritis.3 at breeding when the cervix is relaxed.3,25 If Ovarian hormones greatly influence the in­ these are not eliminated by about five days flammatory and immune responses of the post-ovulation when the embryo descends to uterus. These defense systems have the the uterus, infertility may result.3 Mares can greatest ability at estrus when the vascular conceive while infected, but many will abort, system is the most permeable.32 Progesterone 28 resorb, or produce infected foals. 9 Pyometra inhibits the immune response. Many mares occasionally occurs, but does not show sys­ become anestrus after embryonic loss, delay­ temic manifestations as in the canine.20 ing the next estrus for a significant period of The mare has a highly efficient defense time.23 Infrequent, irregular estrus due to em­ mechanism that clears the uterus of bacterial bryonic loss and decreased ovarian activity is contamination, so inflammation is a normal common in the least productive mares. 21 Em­ response in fertile mares.3 This mechanism bryonic losses occur because of nutritional de­ involves phagocytosis by neutrophils, primar­ ficiencies, endometrial disease, stress, twin­ ily, which respond to a massive invasion of the ning' paternal influences, chromosomal uterine lumen by debris and bacteria within 6 aberrations, failure of maternal recognition of hours.1,27 Opsonins from the circulation are pregnancy, and several other causes. Mares vital for efficient phagocytosis, and comple­ may have lower conception rates when bred ment is a component of opsonization. 1 The on the foal heat.28 The highest percent of pregnancy loss occurs at days 15 - 20, when *Dr. Ebert is a 1985 graduate of the College of Veteri­ maternal recognition occurs, or at days 30­ nary Medicine at Iowa State University. **Dr. Riese is a professor of Veterinary Clinical 35, just prior to when the endometrial cups Sciences at Iowa State University. form. 23 12 Iowa State University Veterinarian There are a variety of anatomical and con­ DIAGNOSING INFERTILITY genital conditions in mares that contribute to A diagnosis of infertility and its underlying infertility. Pneumovaginitis, and subsequently etiology is based on a complete and careful pneumo-uterus, result from poor conforma­ evaluation that may require several clinical tion which allows an inadequate vulvo-vesti­ and laboratory procedures. Uterine cultures, bular closure and urine pooling.20,28 Occa­ uterine cytology, endometrial biopsies, sero­ sionally' maiden mares have a persistant logy, endoscopy, ultrasound, and rectal palpa­ hymen.2o Chromosomal abnormalities may tion are common techniques available to the be related to bilaterally small, smooth, soft or practitioner.20 firm, ovaries with no palpable structures.8 A general physical appraisal should be the Pathologic cystic follicles, like those in cattle, first procedure when evaluating the reproduc­ have not been documented in mares.8 Cervi­ tive status of a mare.26 The overall condition cal lesions prevent conceptions in some of the mare in terms of her body fat can have mares, and are frequently a result of trauma a direct effect on her reproductive efficiency. from breeding or foaling. 20 Mares are most fertile when they are lean and Ovarian neoplasm can cause infertility. gaining weight.7 Any masculinity should be Three recognized categories of tumors are sex noted. cord-stromal tumors (granulosa cell tumors), The reproductive exam should begin with a primary eptithelial tumors (cystadenomas), visual appraisal of the vulva, vagina and cer­ and germ cell tumors (teratomas and dysger­ vix. 26 Conformational and traumatic defects minoma). Of these, the granulosa cell tumors are common. Recto-vaginal tears, pneumova­ are the most common.8,24 The embryologic gina (windsucking), cervical lacerations, mus­ origin is uncertain. They produce hormones cle separation, abscesses, diverticulae, and and cause anestrous, intermittant or frequent abnormal dilatation ofthe cervix can be found estrus, nymphomania, stallion-like behavior by visual inspection with a speculum or digi­ or masculine physical characteristics in mares tally.7 A rectal exam is the most important because of the increased testosterone concen­ step in reproductive evaluations. The uterus tration.24 can be palpated to determine its tone, size, and texture. The ventral wall at the junction The serous cystadenoma is rare. Mares will of the horns is the most frequent location for cycle normally, and can become pregnant due grossly palpable uterine pathology7. Atrophy to the normal function of the opposite ovary. of myometrium, mucosal atrophy, endome- The multiple cysts eventually destroy the af­ fected ovary.20 They do not secrete hormone. Teratomas are relatively rare and are non­ TABLE 1. Differential Diagnosis of Ovarian Enlargement8 hormone secreting. They can be quite large Granulosa Cell Persistant Follicular Ovarian Tumor Structures (Functional) Hematoma and contain bone, cartilage, hair, teeth and Age Breeding Age Usually Breeding Age Us. Br. Age nerves. They are usually unilateral and the Site Unilateral Us. Unilateral Us. Unilat. opposite ovary will cycle and pregnancy is Season All Year Breeding Season Peak Br. Sn. possible.20 Estrous Anestrus, Anestrus, Normal, Cycle Irregular Nymphomania, Fertile. Dysgerminomas are rare but are the one Charact. Cycles, Infertility. Nymphomania, malignant form of ovarian neoplasms. They Infertile. metastasize to the abdomen and thorax and Behavior Normal to Abnormal- can cause colic or rapid weight loss. 20 Virilistic, Viscious. Endometrial cysts develop from obstructed Ovarian Varying size, Large cystic struct. Large cystic Charact. Solid, cystic, Fossa palpable. structure. lymphatics in the reproductive tract. These Indistinct Cyst fluid serous. Architecture Fossa. destroyed. cysts, if large enough, make the endometrial Serous Fluid. Bloody fld. lining unsuitable for implantation.20 Response to Infertility can be recognized by anestrus be­ Hormones Fair havior during the breeding season in unbred Treatment Hemi-ovar- Hemi-ovariectomy. Hemi-ovar- iectomy Ovariocentesis. iectomy. mares, continuous or intermittant estrus, ag­ LH/HCG, Progesterone. Recovery. gressive behavior, uterine discharges, or a his­ Prognosis Good Good Good tory of unproductiveness.8,24 Wk-months Days to weeks A few days Vol. 48) No. 1 13 trial cysts, and lymphatic lacunae can be de­ there is evidence of infection visually or tected, as can atrophy of endometrial folds. biopsy indicates active inflammation.7 Dis­ Oviducts cannot be consistently palpated. charges should be noted, although only conta­ The ovaries should be examined for hypo- or gious equine metritis can be diagnoised by the hyperplasia. The normal size is 6-7.5 cm in type of discharge (grey).9 Pure cultures on length, but vary greatly in size due to the sea­ successive days are more meaningful.7 Signif­ son.7 Their consistency, and a comparison icant bacterial