This post briefly outlines the four most common complaints concerning reproductive behavior in mares: (1) failure to show estrus or to stand for breeding, (2) maternal behavior problems, (3) stallionlike behavior, and (4) estrus cycle-related performance problems in mares.
Failure To Show Estrus Or To Stand For Breeding
Research and clinical experience consistently indicate that most mares show estrus, or some detectable and reliable change in behavior consistent with estrus, in association with ovulation. A stallion given free access to the mare probably would have no difficulty detecting estrus and proceeding with normal breeding. A trained and careful observer would see changes in response to prolonged interaction with a male. Therefore “failure to show estrus” or “silent ovulation” in most cases represents management failure to adequately elicit and/or detect estrus under farm conditions. Difficulty detecting estrus also is complicated in certain individual mares that may naturally show good estrus for only a few hours.
The recommendation for detection of estrus in mares is teasing for at least 5 minutes, preferably with the mare at liberty to approach the stallion, along a fence line or with the stallion in a teasing pen. This enables a fuller range of mare estrus behavior and avoids submissive behavior evoked by forced encounter with the stallion. Sometimes it helps to tease with two or more stallions (sequentially for at least 5 min each).
Some mares show estrus during teasing and then fail to stand for mounting. Normal fertile mares pastured with stallions often are observed to go through periods of alternating solicitation and rejection of the stallion. This natural tendency for ambivalence may account for some of failure to stand for breeding in hand-breeding. Another factor in failure to stand for breeding appears related to severe restraint of the mare and limited precopulatory interaction with the stallion at the time of breeding.
Heterotypical behavior, that is, abnormal behavior typical of the opposite sex, in mares includes fighting with stallions; elimination-marking behavior (olfactory investigation, flehmen, and marking of excrement); herding teasing; and mounting mares. It is caused by exposure to androgens or high levels of estrogens that convert to androgen. The most common source of androgens in mares are granulosa cell tumors and administered steroids. Removal of the source of androgens generally leads to cessation of stallionlike behavior within weeks to months.
Stallionlike behavior occasionally is observed during mid pregnancy. At one time this was attributed to androgens in a male fetus, but it has been observed since in mares carrying females.
Estrus Cycle-Related Performance Problems
Temperament and performance of mares can vary with the ovarian cycle, with some mares showing more or less desirable behavior during diestrus, estrus, or anestrus. Complaints require careful, detailed analysis of the specific desirable and undesirable behavior in relation to ovarian activity. Careful evaluation of complaints may reveal a physical, handling, or training problem that may be either unrelated to the ovarian cycle or that may worsen with estrus as many physical problems do. In evaluating complaints, a common finding is that owners and trainers are unaware of the specific behavioral elements of estrus and diestrus, often confusing the two states, and sometimes assuming estrus equals bad behavior. When it is confirmed that problem behaviors are associated with the ovarian cycle, improvement can be achieved with suppression or manipulation of the cycle using progesterone, hCG, and prostaglandin as recommended in “Induction of Ovulation.” A large percentage of such complaints involve submissive cowering, leaning away, and urine squirting that are easily misinterpreted as estrus. This pattern of behavior often is called “starting gate estrus” because it is common in young anxious race fillies in the starting gate.