The goal of a mare reproductive evaluation or breeding soundness examination is to identify known or potential reproductive abnormalities and to evaluate the potential for a mare to become pregnant and carry a foal successfully to term. Mare reproductive examinations are most commonly performed in open (non-pregnant) mares prior to the onset of the breeding season, problem mares during the breeding season, barren mares at the end of the breeding season, mares with a history of embryonic loss, abortion or other reproductive problems, or as part of a pre-purchase examination.

Reproductive History

All mares should be properly identified, and the breed, registration name, registration number and birth date recorded. Photographs should be taken or accurate drawings of markings and tattoos recorded. A complete breeding history should be obtained, including current reproductive status (maiden, barren, pregnant or foaling), number of cycles bred during the last season, date of last breeding, breeding technique used (artificial insemination, natural cover or pasture breeding), date of last foal, number of previous foals and any previous history of abnormal estrous cycles, uterine infections, embryonic loss or abortion.

Physical Examination

A general physical examination should be performed in addition to the reproductive examination to assess whether the mare has the capacity to carry a foal to term. The evaluation should include, but is not limited to, examination of the oral cavity, eyes, respiratory, cardiac and musculoskeletal systems. In addition, diet and body condition should be evaluated. Broodmares do not have to be fit for athletic competition, but they should not be severely overweight or underweight.

Perineal Conformation

The external genitalia (vulva) should be evaluated for conformation and muscular tone. The optimal perineal conformation consists of a vulva in a nearly vertical position with at least 70% of the vulva ventral to the brim of the pelvis. The muscular tone of the vulva should be sufficient to prevent or minimize aspiration of air into the vestibule or vagina. Horizontal sloping of the vulva secondary to recession of the anus or poor muscular tone to the labia of the vulva may predispose the mare to an ascending infection of the uterus.

Estrous Detection

The mare should be exposed to a stallion with good libido to evaluate estrous cycle stage. Adequate time should be taken to allow shy or nervous mares to express behavioral estrus. When teasing a mare with a foal, the foal must be restrained, and the mare may need to be restrained with a twitch before signs of estrus are exhibited.


The entire reproductive tract, including the cervix, uterus and ovaries, should be thoroughly and systematically examined by palpation per rectum. The tone of the uterus and cervix, size and consistency of ovarian follicles, presence of a recent ovulation, or a corpus luteum, should be recorded. Presence of abnormal ovarian, parovarian (i.e., fimbrial cysts) or uterine structures should be recorded.


Manual palpation should be followed by a systematic ultrasound evaluation of the entire reproductive tract. Ultrasound is used in broodmares to visualize structures in the reproductive tract that cannot be palpated or differentiated on palpation per rectum in the early diagnosis of pregnancy, diagnosis of twins and evaluation of potential ovarian or uterine pathology.

Vaginal Speculum Examination

A vaginal speculum examination is performed to evaluate the anatomy of the vagina and the external os of the cervix. Speculum examination is useful in determining the stage of the estrous cycle (via cervical morphology), urine pooling and the presence of cervical inflammation or discharge.
Digital Examination of the Cervix. After the speculum examination is completed, the cervix should be examined manually for patency and the presence of abnormalities, such as adhesions, lacerations or other defects.

Uterine Culture

Culture of the uterine lumen is usually done in conjunction with cytology for the diagnosis of endometritis. Endometritis can be suspected in mares that exhibit an abnormally short estrous cycle, vaginal or cervical discharge, inflamed cervix on speculum examination, free fluid in the uterus during diestrus detected on ultrasound, and possibly failure to conceive when bred to a fertile stallion. Bacterial and fungal endometritis are significant causes of reproductive failure in broodmares. Uterine culture samples can be collected using a guarded swab or a low-volume lavage. Samples are processed and interpreted by the professional staff at the Equine Reproduction Laboratory.

Uterine Cytology

Cytologic evaluation of the uterus involves the collection and interpretation of cells lining the uterus (endometrium) and within the uterine lumen. Cytology is used in conjunction with culture and biopsy in the diagnosis of endometritis. Advantages of endometrial cytology for diagnosis of endometritis include the ease of sample collection and rapid availability of results. Endometrial cytology is one of the least expensive and most useful techniques routinely used by equine practitioners to detect the presence of endometritis. Cytology samples can be collected using a guarded brush or swab, or using a low-volume lavage. Samples are processed and interpreted by the veterinary staff at the Equine Reproduction Laboratory.

Endometrial Biopsy

The endometrial biopsy technique involves collection of a small sample of the uterine lining (endometrium) for histologic evaluation. It is primarily used as an aid in the diagnosis of uterine disease and as a prognostic indicator of the ability of a mare to carry a foal to term. An endometrial biopsy can also be used as the sample source for culture and cytology evaluation. Endometrial biopsy samples are collected at the Equine Reproduction Laboratory and submitted to the CSU Veterinary Diagnostic Laboratory for processing and interpretation.

Additional Tests

The standard examination procedures in the mare breeding soundness examination may not identify the cause of subfertility. Consequently, other examinations may be indicated, including hormone analysis, chromosome analysis (karyotype), videoendoscopy (hysteroscopy) or other tests.