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EquiSearch’s Ask the Vet: Aggressive Behavior

When a reader's mare becomes increasingly aggressive, Dr. Joyce Harman offers possible explanations, most of which relate to pain, in's Ask the Vet.

Photo by Hunter Messineo
When a horse becomes overly aggressive, restrict his access to other horses and people.
Photo by Hunter Messineo

Question: We have three horses: two mares (ages six and seven) and a gelding (age four). The six-year-old Arabian mare, Pasomia, is extremely "pissy." She has been a wonderful horse for our children to learn everything about riding. However, she is becoming increasingly hateful.

Pasomia has always been the dominant mare. We have been through two horses, and she was fine with both at first. We kept them separate for several weeks, then allowed over-the-fence contact and finally put them together. In the last six months she is becoming more "crabby." I follow many of Clinton Anderson's techniques on ground manners, so when she's working I have her respect, and she's a good girl.

Lately she has taken to pinning her ears at all humans in or around her with or without any horse within 50 yards. She pins her ears and threatens anyone at feeding time as well. I am baffled as to why. It seems to be getting worse--so much so that I don't allow my children to feed her anymore. I work with my kids to make them understand ground discipline with her. They follow through well and are only allowed to work with her when we are out there working with them as well.


What can I do about her aggressive tendencies? This week she bucked my nine-year-old twice and me once. I will not tolerate that behavior. Also she kicked out at me four times yesterday when I was having her yield her hindquarters in either direction. I had her checked at a local equine facility and got a clean bill of health. I had my farrier/adjuster work out all her kinks physically. Every six weeks we trim and deworm. She bucked both bareback and saddled (I thought perhaps the saddle was bothering her).

We have decided to put her alone in our arena/spare paddock and not allow her contact with the other horses because she is so horrible toward them and horses through our neighbor's fence.

Do you have any training/corrective suggestions?

Answer: You are correct to restrict access to her to keep people safe, and I would continue to do that until the problem is solved.

There are many reasons a horse becomes more aggressive, and most relate to pain in some way. Any horse that was fine for years and now is not, you have to ask the question as to why and sometimes look deeply for the answers. Most people want to solve behavior problems with training and keep looking for techniques, either kind ones or others that involve bigger bits and bigger spurs. But in reality most behavior problems are related to pain. Your job is to find the pain. Making her move away from you, like moving her rear end, or making her move her feet or otherwise trying to convince her you are the lead horse does not solve the problem.

You have had her checked at the vets but do not say what all they looked at. Sometimes a general checkup will not reveal everything. Many vets do not understand the effects of back pain on behavior, and many are not really familiar with diagnosing back or general musculoskeletal pain when the horse is not lame.

Also, many horses with pain and grumpiness have ulcers, even if they eat well and look to be keeping a good weight. You may want to have her scoped to look inside her stomach. Or you could try an herbal formula such as Hilton Herb's Digest Support or Succeed and see if she feels better. Either product is safe and helps a lot of horses, sometimes just enough to convince you to have her checked out more fully for ulcers (we have talked about ulcers in another Ask the Vet).

Also, mares can get a tumor which produces testosterone (male hormones) or can put their hormones out of balance. Sometimes a blood test to check hormones is a good idea. I would certainly have her get a rectal examination to check for a tumor or ovary that could be painful, cystic or abnormal in some way.

You say you had a farrier/adjuster check her out, but in reality many untrained individuals can do more harm than good in the long run, even if the horses seem better in the short term. Personally I would not recommend that anyone use any sort of chiropractor, adjuster or manipulator that is not a licensed human chiropractor, osteopath or veterinarian trained in those modalities. Any chiropractor or osteopath who works on people first should have extensive training on animals before allowing them to work on your horse. Even then, you need to be sure the techniques are gentle and that results are obtained. Some gentle techniques with an untrained person are kind but do not address the problem. Rough techniques can damage ligaments, tendons and joints as well as cause disc injuries.

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