The Question: Why does my mare kick, bite, and urinate on a gelding she's turned out with?

I own a 15 year quarter horse mare named Lark. When I bought her, she was with two geldings where she was the boss mare. Then, she was pastured with a young mare who was submissive and afraid of her. I moved her to her own barn, where she was by herself for several months before another young mare was put with her. They bonded instantly and it was as though Lark was the other horse's mother. The young mare followed Lark every where at her flank. That mare left and was replaced with a older but submissive mare (Tihyme) whom Lark got along with fine. The submissive mare and Lark were then moved to a boarding stable where there are eight other horses. Following a two month adjustment period, Lark was then introduced into the herd where unfortunately, she and another mare tangled and she got hurt. For two months, she was on stall rest and her pasture buddy, Thyme, was sold.

After Lark had healed sufficiently, we started to turn out with another horse, who was lame. A gelding named Corky. At first, this situation worked. Corky and Lark got along fine for about a month. Then, Lark decided she didn't like Corky and would run him off. We put Lark in with two geldings, a young one named Junior and an older gelding named Smoke. Lark is fine with Junior and she has attached herself to Smoke. However, whenever she sees Corky, she puts her ears back, bites him in the butt and turns and lets loose with a stream of urine. After that, Corky moves away from her and things are fine. She is currently out to pasture with Junior, Smoke, Corky and a small pony gelding named Toby.

My question is why does she act that way towards Corky and why does she urinate on him? It is every time we put them out to pasture. She doesn't hurt him with her bites or her kicks at him, she just goes through the motions and then urinates. Is there a way to control this?

She had been in heat for four months and I had my vet do an ultrasound on her to check for tumors, and blood work to check her hormone levels. Everything is normal. We put her on Regumate for 12 days and observed no difference in behavior.

The barn owner is suggesting that I sell her and get a gelding. Lark is a good horse except for this urinating behavior which she has just developed over the past two months. Could it have something to do with all the stress she has been under with her accident (bone chip in rear long pastern bone) and her buddy being sold, plus the many moves in short period of time. In the stall, she is well behaved except for some excitement at feeding time. When I ground handle her she is great. She has never tried to bite or kick me. She lifts her feet for you before you ask and lowers her head to put the bridle and halter on. We have used her as a lesson horse for our first year riders, just walk and trot. She did great! I really don't want to sell her if this behavior problem can be solved.

The Answer

Howdy.

Wow! What an interesting question. I think you've got a few things going on that I want to address.

First, you said your mare has been in heat for four months. Your vet has checked her out, but he's found nothing unusual. However, a horse in heat for four months is not normal. I would get a second opinion, preferably from a veterinarian with expertise in mare reproduction.

Prolonged heat such as you describe can be a sign of a tumor or other disorder which can lead to aggressive behavior - although since your mare displays this behavior towards only one horse, I'm not sure that's the real problem.

It may just be a personality conflict between your mare and Cody. Horses are like people - they get along well with some horses and don't get along with others. Since she's getting along well with everyone else, this would be my guess. You may just have to separate Corky and Lark.

Good luck with your mare - I wish I could have given you advice that's easier to work with. But unfortunately there are some things we just cannot change, and so we have to work around them.

The Equine Behaviorist

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