Help! My Mare Is Acting Like a Stallion

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My mare becomes very demanding at feeding time, is pushy with other horses and people, and in general can be far too aggressive in social settings with horses and people. At other times she can be gentle and cooperative, but that is usually when it's one to one with a person or another horse.

Answer: The more horses and people there are around, the more your mare is prepared to act aggressively. Aggression usually comes from feeling afraid, either because the horse perceives there to be threats to personal safety, or competitive threats to her share of resources (food, friends, shelter and so on).

Get good at reading the subtle nuances of your horse's body language – tight lips, wrinkles over the eye brows, tense muscles, high head carriage, clamped tail and shallow breathing are all things we can watch out for.

The most likely cause in a case like this is medical: A granulosa cell tumour (GCT) of the ovary. Up to 60% of mares with GCT in one study alone exhibited stallion-like behaviour, especially aggression, and were also found to have high testosterone level. The the ca cells in the tumour produce testosterone.

Other signs of GCT, especially a chronic one are muscular physique, especially the neck, an enlarged clitoris, and no ovulatory cycle.

Your veterinarian will investigate for GCT by rectal palpation and ultrasound scanning of the ovaries - the tumour takes on a honeycomb appearance. Blood is also taken to check out hormone levels – inhibin levels are high in 90% of cases of GCT interrupting the normal estrus cycle, with testosterone being high in 50-60% of cases.

It is testosterone that causes the increased aggression and physical changes. Otherwise, estrogen levels tend to be normal, and progesterone levels are very low. Mares with GCT are more sensitive to life's niggles, especially competitive threats, so are more likely to be aggressive in a group situation. This is because testosterone sensitizes the parts of the brain involved in detecting threats and using aggression.

Understanding aggressive behaviour in your mare

Understanding aggressive behaviour in your mare

Aggression usually comes from feeling afraid, either because the horse perceives there to be threats to personal safety, or competitive threats to her share of resources. New window.

Mares like yours can be worse when people are around because their attention may be something to fight over – such as when horses are brought in from the pasture at feeding time. Additionally, certain people may be a threat, creating anxiety about what they may do.

If people, and other horses, are seen as both good and bad, because they've been friendly and aggressive (often for fear of aggression from the mare!), the mare will feel mixed up about their intentions. This can make her to want to approach and escape all at the same time, increasing the tendency to behave aggressively!

The one-to-one situation is more straightforward because there is no threat of competition from others, and the behaviour of the other – human or horse – may also be more relaxed and consistent as a result.

The usual treatment for GCT is surgical removal of the affected ovary. Afterwards the hormonal cycle takes a while to normalize, usually 6 – 8 months, so in the following breeding season. In some cases the normal cycle returns in as little as two months.

Horses are seasonal breeders and so mares don't ordinarily cycle in the late autumn and winter. Once the affected ovary has been removed, the testosterone levels should drop quite quickly, after all there is no GCT to continue producing it.

This means that the aggression should also subside, however there may be some lingering learned effects. The key triggers for aggression in cases like this tend to be other horses (or people) in close proximity, because this triggers the feelings of coming under threat.

Counter measures to help decrease aggressiveness

1. Good counter measures include keeping the social situation easy to deal with, a small herd numbering 3 or 4 individuals who are all generally relaxed and confident with good social skills – not aggressive or insecure.

Pertinent to this case, aggressive individuals tend to be avoided by other horses. A mare who is aggressive will be more able to relax and gain social confidence if she is not housed or pastured with another aggressive individual.

2. Another good counter measure is to make sure that there are plenty of resources available to all the horses in the group. Enough dry area to stand around on, enough space where they can all shelter from harsh weather conditions such as strong sun, as well as wind and rain. Enough room at the hay feeder, or spread supplementary hay out so that there are more spaces to eat at than there are horses in the group.

Also make sure that feeding stations are more than two horses' length apart or more, so individuals can use them without fear of being harassed by another. Water should be placed away from gateways, and ideally in a large container than the horses can gather around, such as the large round troughs used for cattle.

Separate horses in order of competitive tendencies – the most pushy first – when giving concentrate feed in order to maximize predictability and minimize the need to fight.

3. The third important counter measure is human behaviour. We need to be calm and predictable, and avoid using actions that cause horses fear. We should also be mindful of how close we bring anxious and aggressive horses to the things they fear, such as other horses.

Going closer when our horse is calmer, and going back to a safer distance before they get upset is paramount to avoid them becoming unduly stressed and resorting to aggression.

Read nuances of mare's body language and reward calm behaviour

Get good at reading the subtle nuances of your horse's body language – tight lips, wrinkles over the eye brows, tense muscles, high head carriage, clamped tail and shallow breathing are all things we can watch out for.

Reward calm behaviour with your attention, and a good scratch in a favored place such as over the withers. Remember that release from a stressful situation is just a relief – would the horse voluntarily go back there just to get that release again? Above all, take your time, your horse needs you to pay attention and be responsive to their needs.

What if a veterinary exam turns out that your mare is not affected by GCT? These counter measures still apply. Also, ask yourself, what has happened to cause my mare to be aggressive? When was the first time this happened? What triggered it? How did others (horses and humans) respond to her? You may find some vital clues that will help in rehabilitating her.

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This easy to read book: The Horse Behavior Problem Solver: All Your Questions Answered About How Horses Think, Learn, and React will help you understand why your horse acts the way she does as equine behavior expert Jessica Jahiel offers proven solutions to common horse behavior problems.

Read this popular book by Cherry Hill, How to Think Like A Horse: The Essential Handbook for Understanding Why Horses Do What They Do for a better understanding of what motivates horses, how they experience the world, what makes them happy, and what worries them.

About the author

Jenni Nellist is one of Great Britain's most popular equine behaviorists. She provides consultation services to help people who are interested in learning about equine behavior.

Search for new learning took Jenni to the university in Aberystwyth and an equine science degree. There she learned that not all the answers are actually available and that she would have to question things for herself and learn how to test ideas in order to form her own opinion.

In her twenties, Jenni practiced what she had learned, and through trial and error, established a practical hands-on understanding of techniques that would lead to horse training success.

In order to make sense of what she was exploring she went back into education, this time an MSc in Companion Animal Behaviour Counselling at the University of Southampton. Really understanding how horses function, at all levels, makes it possible to understand why problems arise and to go about tackling an individual’s problem humanely without becoming method bound.

These days she spend most of her week working with horse owners who are seeking knowledge in order to improve their own horsemanship skills and resolve a great variety of training and behavioural problems.

Visit Jenni's Website to learn more about her services. Jenni also invites you to visit her facebook page.