Evaluating reproduction-related behaviour and performance problems in mares

Abstract

In this issue, Dr. Robert Dwyer describes a clinical case of a 7-year-old riding mare presented in early spring of each of two consecutive years for evaluation of persistent oestrus-like behaviour, intermittent aggression with herd mates and a decline in compliance during ridden work (Dwyer, 2025). At the time of presentation, the reproductive tract was found to be normal, with two notable exceptions: (1) vulvar asymmetry with incomplete labial apposition, and (2) two soft tissue bands connecting the left and right ventral vulva and another connecting the left and right vaginal walls at the vestibulo-vaginal fold. Testosterone, progesterone and anti-Müllerian hormone levels were within normal reference ranges. The ovarian findings were consistent with vernal transition. Karyotyping revealed mosaicism. Interventions included transecting the bands of tissue and GnRH vaccination. At follow-up examination 6 months later (autumn), the ovaries were found to be small and inactive. The owner reported improvement in behaviour. Dr. Dwyer wisely concludes that the mosaicism is an interesting finding but may be incidental.

Whenever equine reproduction, behaviour or sports medicine specialists gather, the conversation inevitably turns to the challenges of evaluating mare behaviour and performance cases. Dr. Dwyer's case nicely illustrates some of these challenges. It is a pleasure to have been invited to preview this report and share my comments based on experience with clinical evaluation of similar cases of mare behaviour and performance problems.

One of the key challenges not directly addressed in Dr. Dwyer's case report is that oestrus in mares is often poorly understood. When we ask owners and trainers to describe the specific elements of their mare's behaviour, we often find that what they describe does not align with oestrus. In our experience, the behaviours described are often more consistent with physical discomfort. For instance, vocalisations, urination, tail movements and cowering typical of guarding behaviour are commonly mistaken for the distinct vocalisations, tail movements, urination and leaning behaviour of oestrus. Many owners are not aware of the nature of oestrus during seasonal transition. Another reason we ask owners and trainers about the specifics of their mare's oestrus behaviour is that we often encounter the assumption that nearly any reduction in compliance with work or undesirable behaviour—such as stopping, refusing to go forward, kicking at the abdomen, sensitivity to touch or ‘girthiness’—is indicative of oestrus or ‘marish’ behaviour. We actually prefer to observe the behaviour firsthand, either in person or video recordings. Our evaluation includes presenting the mare to a stallion (or playing recorded stallion vocalisations and/or offering soiled bedding from a stallion if a stallion is unavailable), as well as to another mare. The mare's response, together with the stimulus animal's response, can be evaluated in the context of the mare's ovarian status at the time. This raises an important question: was the behaviour truly oestrus in Dr. Dwyer's case? Additionally, we routinely obtain a 24-h video sample of the mare's behaviour in the absence of perceived threats or interactions with people. This is especially helpful for identifying discomfort behaviours that may underlie performance or behavioural issues, as well as localising the source of discomfort (Torcivia & McDonnell, 2021). Moreover, subtle male-typical elimination/marking behaviours, if present, can provide valuable diagnostic information regarding androgenisation.

In our experience, perhaps the most common cause of discomfort behaviours misinterpreted as oestrus is urovaginal irritation, including tissue bands like those described in this case. This type of irritation seems to be particularly aggravated during oestrus. As Dr. Dwyer alludes, there is a good chance that releasing those bands contributed to the mare's reported improvement.

As in Dr. Dwyer's case, many mares referred to our reproductive and behaviour team for evaluation have already been treated with altrenogest or other progestins to suppress oestrus. Often, this occurs before the problem emerges. Seasonal or year-round treatment is sometimes considered routine in North American equine competition culture—almost akin to nutritional supplements. In addition to daily oral altrenogest, many of our referral cases also receive a variety of supplements marketed specifically to address ‘marish’ or ‘moody’ behaviour, or perceived ‘hormone imbalances’. This makes evaluating normal ovarian function more challenging. Few owners or practitioners realize that prolonged exposure to or high levels of altrenogest, and possibly other progestins, can lead to problematic behaviours that further complicate the clinical picture. For example, in research conducted in our herd at the University of Pennsylvania, some of the mares treated with a slow-release progestin formulation developed male-typical aggressive and sexual behaviours (unpublished observations).

In addition to progestins and supplements, our referral cases often also involve a history of handling or training interventions that further complicate the diagnosis. For instance, aversive methods may be used to force performance or punish undesirable responses, which can escalate avoidance or escape behaviours—such as rearing, biting, kicking or bucking—that might be misinterpreted as ‘marishness’, generally poor temperament, or often stallion-like aggression. In some cases, mares have been passed to new trainers or owners. It is not unusual for behaviour modification to improve performance temporarily, particularly with a change of environment or trainer. This phenomenon of fear and stress temporarily overriding discomfort and increasing compliance aligns with equine ethology and behaviour modification science, but can easily lead to a misunderstanding of the root causes of the problems.

The equine industry worldwide is now seriously confronting the risks of loss of social licence to operate, particularly for the use of horses in sport. I believe this is an area where veterinary practitioners—especially those working with competition horses—can make a significant contribution to improved welfare. A comprehensive evaluation from the outset, with consultations and referral as indicated, can help reduce suffering and improve outcomes. For example, rather than initially defaulting to a progestin trial, a thorough ‘package evaluation’ should be recommended from the start (McDonnell, 2017). This approach should confirm whether the behaviour is related to the ovarian cycle, evaluate for physical discomfort (such as gastric ulcers or musculoskeletal pain), and identify any other potential underlying issues. A 24-h video sample of the mare in her stall, evaluated by a behaviour specialist experienced in recognising and localising subtle discomfort behaviours, can be extremely helpful. In the long run, this approach is usually less costly and frustrating for owners, and it can improve the well-being of the mare as well as improve equine education.

None.

No conflicts of interest have been declared.