Equine Self-Mutilation

There are at least three distinct types of self-mutilative behavior in horses. Here’s what researchers know about them and how management changes and other options can help reduce their frequency.

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equine self-mutilation
Flank-biting or flank-sucking is a cluster of behaviors called self-mutilation and horses can incur serious self-injury during these episodes. | Photo: The Horse Staff
It’s a beautiful winter weekend, and finally you have a full morning to spend at the barn. You’re happily grooming your horse when you notice a cluster of patches of wet hair on his side. Peculiar pattern to the wet hairs—all are lying forward as if combed with a wet brush. Oh well, odd but probably nothing, you think. But wait, some of the wet spots have hairs missing or chopped off bluntly. You check the other side, and there you find some more patches, like the wet ones, but as if they have now dried. What’s going on? There are more of these patches on the left side than on the right side, but they all are in the same area of the abdomen, from the ribs to the stifle.

Just then the barn manager comes in all excited. She’s glad you’re there early today, because when she was feeding this morning, she found your horse spinning in his stall, tearing at his blanket and biting at his sides. Her first reaction was to scream at him to stop—and he did. She figured the blanket was the problem, maybe it was rubbing or pinching him under the leg. She got some help to investigate. They couldn’t find anything out of order with the straps or the blanket, but took it off anyway. Then, just as they closed the stall door, he really went nuts, spinning in a very tight circle, biting his left flank. With each bite, he squealed and kicked out. As he was turning and nipping, he sometimes was bucking and squealing. They were too scared to open the door. He went on for what seemed like forever, as if he wouldn’t stop until he tore up the stall or killed himself. Then he gradually came out of it.

“When we screamed his name, he turned toward the stall door, looking at us with a sort of a worried, glassy eye, like he didn’t know what was happening. We threw him his hay, and he’s been pretty quiet since.”

You run your fingers over the wet areas on his flanks and feel some crusty bumps on the underlying skin. Separating the hairs, you can feel little marks in the skin—anywhere from one-quarter to one inch in diameter. Some are fresh nicks, some are scabbed over, some look healed. The rest of his coat is unblemished. No marks, no wet spots, no chopped or missing clumps of hair other than on his flanks and over his ribs

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Written by:

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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