A breeding soundness examination should begin with a gathering of all pertinent reproductive history regarding the mare. A thorough history may uncover information about a mare that may not otherwise be obtained. For instance, the following queries should be answered: How old is the mare? Has the mare been bred previously? If so, has she become pregnant and delivered any foals? How many foals? How long since she last foaled? Has she been bred each year? Has she been bred to fertile stallions with good breeding management procedures? Has she been bred to different stallions each year? Has she had any difficulties associated with foaling? Were any diagnoses of early pregnancy loss confirmed? Has she had any abortions or stillbirths? If so, at what gestational ages were pregnancies lost? Has the mare had any genital discharges? Has the mare previously been treated for genital infection? If so, what treatments were administered and when?

Mare age is important because, as a population, mares become less fertile with increasing age. A recent study involving Quarter Horse–type mares in good body condition revealed that for every year increase in age, the odds ratio for becoming pregnant on foal-heat breeding was 0.937 (i.e., approximately a 6% lower chance of becoming pregnant). In another study that investigated some of the factors affecting fertility in Thoroughbreds bred in central Kentucky, once mares passed the age of 10 years, odds ratios for becoming pregnant during the season significantly declined (Table 4-1).

The status of the mare at the beginning of the year (i.e., foaling mare, mare that delivered a foal that year; maiden mare, mare that has not been bred in previous years; barren mare, mare bred the previous year that did not become pregnant; not bred mare, mare that the owner elected not to breed the previous year; or aborted mare, mare that became pregnant the previous year but lost the conceptus before a live foal could be born) can also be a significant predictor of expected fertility. A number of studies have identified maiden and foaling mares as the most fertile groups in broodmare bands; other groups of mares (particularly barren mares) are usually less likely to become pregnant and produce foals.

One should also collect information regarding the mare’s estrous cycle. Mares are seasonal breeders with the peak of fertility corresponding to the longest days of the year. The mares typically have normal estrous cycles during the physiologic breeding season (spring and summer), then enter a state of reproductive quiescence in the late fall, as day length decreases. Mares that are reproductively normal generally enter into estrus (heat) every 18 to 24 days (approximately every 3 weeks) during the breeding season, with heats that typically last for a period of 4 to 7 days (see Chapter 2). Because of seasonal variations in the duration of estrus, a better indicator that the mare has regular estrous cycles is that the period between heats is 14 to 16 days. This interval remains relatively constant regardless of season. Whether or not the mare has normal estrous cycles and exhibits strong outward signs of heat (i.e., is sexually receptive) when exposed to a stallion during estrus should be noted. In addition, the method of teasing should be obtained because most mares fail to show strong signs of estrus unless teased by a stallion. Numerous mare owners believe otherwise, yet we have teased mares with a stallion when the owners thought the mares were showing heat to a gelding or another mare, often finding the mares were not in estrus. In contrast, we have also teased mares thought by the owners to be out of heat when we suspected they actually were in heat (based on palpation findings) and usually found that the mares express behavioral estrus when presented to a stallion.

Shortened estrous cycles (e.g., less than 18 days) suggest the possibility of an underlying uterine infection (i.e., acute endometritis causing premature luteolysis). Lengthened estrous cycles in nonbred mares suggest the possibility of prolonged luteal function; in mares that have been bred, the possibility exists for early embryonic or fetal death. A less likely cause of irregular estrous cycles is endocrine dysfunction. If a mare has regular estrous cycles, the likelihood of endocrine dysfunction is low.

If possible, the examiner should collect previous breeding and medical records regarding the mare of interest and determine specifically whether the mare has had any reproductive or general medical problems that have necessitated treatment. A variety of ailments may reduce or abolish a mare’s reproductive potential. A sample breeding soundness examination form for recording of history, examination findings, diagnosis, and treatment recommendations is provided in Figure 4-1.

Just because a mare is being examined for reproductive potential does not mean that her general body condition should be ignored. Texas workers, using a body condition scoring system of 1 to 9, found that mares with body condition scores of 5 or more had higher pregnancy rates and fewer cycles per pregnancy than mares with lower body condition scores. They also found that mares that entered the breeding season in high body condition, and were maintained in high body condition during the season, had earlier onset of regular estrous cycles and higher pregnancy rates and were less likely to lose pregnancies than were mares that entered the breeding season in poor body condition or that lost body condition during the breeding season.