Problem Behaviors in Pastures

I recently purchased a 4-year-old gelding. He is extremely aggressive toward my other gelding in the pasture, and I'm unable to turn them out together. I am able to turn the horse out with my pony mare and pony gelding, but he "herds" them constantly and often will unsheath his penis and sustain an erection around mares. When left stalled, he exhibits other strange behaviors such as constant stall weaving and defecating in his water bucket. Please advise.                 Martha, Tennessee

Let me start by saying that I have never figured out defecating in water buckets. It happens; I've known several horses which did it, both mares and stallions. In a male, you could imagine it is some sort of marking behavior, since stallions in natural social groups at liberty make stud piles near water holes. Maybe some of our readers have some theories or tested explanations. In your gelding, the defecating in the water buckets might or might not be related to the other problematic behaviors.

The other behaviors you describe--the herding of your gelding and mare, the aggression toward the other gelding, and the sexual arousal around mares--all are probably related. They represent stallion-like behavior. The weaving in the stall might represent his thwarted stallion-like motivation to be out controlling and protecting his herd. Or like the defecation in the bucket, it might be coincidental. If he seems eager to get out of the stall (calling out to the herd, hyperactive) the weaving likely is related to being left behind from his herd that he urgently wants to protect and control, as a harem stallion would.

So why does your gelding act like a stallion? Occasionally, in evaluating geldings with behavior such as you describe, we find that they are not completely castrated. That means they might have some remaining testicular tissue, either a missed piece of testicle or an abdominal testis (cryptorchid) that is producing male hormones that drive the behavior. In fairness to the gelding, and before you try to modify the behavior, I would recommend making sure that this is not the case. The examination can be by your veterinarian with a standard hormone challenge blood test. If there are positive baseline or response levels of testicular hormones, then the tissue can be located and surgically removed (sometimes easier said than done). When the hormones diminish, the stallion-like behavior usually quiets considerably, although not always. (For more on cryptorchids see The Horse of September 1999.)

What if the results are negative, meaning that he is completely castrated, with no remaining testicular hormones to drive this male behavior? Quite a few completely castrated geldings with normally low steroid hormones continue to show stallion-like behavior, particularly under pasture social conditions. Estimates vary, but the percentage might be as high as 50% of geldings which show considerable residual stallion-like behavior.

What can you do about it? You can consider manipulating his social housing conditions to minimize the behavior and/or the resulting problems. For example, you can house him away from other horses all together. Geldings eventually quiet down after prolonged separation from their "herd." You might consider trying to take advantage of natural social suppression of stallion-like behavior by housing your gelding within reasonable proximity to one or more stallions. Most geldings become socially submissive to stallions, and will appear to become demoted to the rank of immature male or bachelor stallion.

The stallion-like behavior that occurs in-hand or under saddle usually can be suppressed with behavior modification similar to that which would be effective for those behaviors in an intact stallion. We know that intact stallions can learn when to "forget" their stallion behavior and take direction from handlers and riders. Administration of the female hormone progesterone sometimes can be a useful adjunct to the behavior modification methods. It tends to suppress male-type behavior and add a generally calming effect. Male-type behavior with herdmates in a pasture usually is very difficult to suppress.

Please keep us posted on how things go.

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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