Mare Aggression

Mare Aggression


Q. I've owned a Paint mare for a year. She has a history of aggressive behavior toward geldings, i.e., will kick out when they're close, but gets along well with other mares. When I am with her in her stall, she becomes very aggressive toward geldings outside by biting the bars and kicking the wall. She always checks to see where I am in the stall first and turns away from me to kick out. She only does this when I'm in the stall. The rest of the time she has little to no reaction to horses walking by. Also, she becomes very protective of me (seemingly) when turned out in a ring by putting herself between me and any other gelding turned out in an adjacent ring. This behavior becomes much more pronounced pre-estrus, making her very difficult to handle around geldings during that time. I have been told that putting her on Regumate will "cure" her "mareish" behavior. Any insights on why she is reacting like this?

Kristie, via e-mail

A. A mare normally shows seemingly protective aggression toward males under a few situations. One is when she is protecting a foal. In that case, the mare would be equally aggressive toward males and females that seemed to be a threat to the foal. Mares don't usually bond to people in the same way they do to a foal, and don't often show protective behavior of the maternal type over humans. Also, a mare is usually only protective of a very young foal. So if your mare is persisting in this behavior and doesn't act this way in the periparturient (just after birth) hormonal state, it is quite unlikely that the behavior you are seeing is maternal protectiveness of you.

Another normal circumstance for a mare to show aggression as you describe is in guarding a prized resource. So if you always give her treats or she sees you as likely to feed her, then she might be guarding you as she might a feed tub. With this situation, she would likely be just as aggressive towards mares, geldings, or stallions.

A more common reason for aggression as you describe in a mare is abnormal stallion-like behavior, caused by abnormal exposure to androgens (male sex hormones). This type of aggression will be more specifically evoked by stallions or geldings than by other mares. The source of the androgen can be internal, as in the case of a steroid-producing ovarian tumor known as a granulosa cell tumor; or the source of androgens can be external, as in the case of treatment with anabolic steroids.

So without further details, or seeing the behavior first-hand, it would be my recommendation to first have a veterinarian rule out an ovarian tumor. This can be done fairly quickly with blood tests and/or a pelvic examination.

About the Author

Sue McDonnell, PhD, Certified AAB

Sue M. McDonnell, PhD, is a certified applied animal behaviorist and the founding head of the equine behavior program at the University of Pennsylvania's School of Veterinary Medicine. She is also the author of numerous books and articles about horse behavior and management.

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