Gelding Herding Mares

Is it possible to change a horse's aggressive behavior? Specifically, I am wondering if there is any information relating to reinforcement contingencies and transfer of learning from a "human-handled" situation to a free-running setting?

The 15-year-old gelding in question (Sass) recently chased some other horses when he was turned out with them, and their owner is worried about allowing him to be pastured with them. We acquired him about a year ago as a trail horse from a friend who had him for a couple of years. Before that, he had been at a place where he more or less had the run of a pasture.

It's not the first time he has chased and herded other horses when first turned out with them, or when he is turned out along the fencelines of mare pastures.

Is there a chance of modifying this aggressive behavior, or is it a situation that will just have to be managed?

He has a lovely temperament otherwise, is polite toward humans, and doesn't really have any obvious vices. However, he sometimes acts like a stud--very alert, tends to be herdbound, very vocal, will put on a display with the arched neck, prancing, etc., around mares, but even then he will respond to my in-hand directions. In the pasture, I've never seen him mount a mare, but he seemed interested in certain mares.

Once, when I let him out alone in the pasture to graze, he ran the fence near a mare, prancing. They were both getting tall and striking out with their forefeet, and the mare would turn her butt to him and urinate.

This spring he cut his pastern and had to be moved into a stall so the wound could be kept dry and clean. Sass seemed upset to be alone at first (the farm owner doesn't really "do" stall board and didn't want to deal with cleaning a second stall so that Sass could have company), but he adjusted to the point where he was mostly calm.

I have looked for articles relating to aggressive stallion and gelding behavior in hopes of identifying some of the reinforcement techniques that would help him in a pasture social situation. I would hate to have him live alone (the farm is not set up for a horse that can't be turned out with the group). Do you think that I can teach him to handle himself more politely (i.e., not chasing the mares) through using an approach-and-removal process as you describe in a number of your articles on modifying breeding stallion behavior? Would this transfer to the situation where he is in the pasture on his own?

He is still in the stall because about nine days ago, we attempted to put him back in with the mares (over about a two-week period, leading up to that, he had been hand-walked in their presence quite often). As soon as I unclipped the lead rope, he started prancing around the paddock, apparently intent on herding the mares. Three of them pretty quickly put themselves into a group and stayed put, but the two who were socially lowest in the group kept running away from him. He chased them through the open gate out of the pasture, and around outside of the pasture. I didn't see pinned ears, but they were certainly running flat out, as if they thought he meant to get them.

The owner of the farm is worried that he will chase the mares to the point where they hurt themselves, and he is unwilling to turn him out with them again.      via e-mail

Your questions of transfer of behavior modification from a "human-handled" situation to a pasture group situation are very interesting. I don't know of any organized research or tested protocols.

My experience and intuition is that it would likely be a very challenging--and in most cases, an ineffective--strategy to try to teach a horse pasture manners.

I have run into people who have tried, mostly with punishment methods such as shock collars, or standing out there with a whip, to try to modify the behavior of their horses at pasture. The stories I have heard are typically pretty hard to listen to, and the results unsatisfactory.

It seems that social behavior that would be normal (and not usually problematic in a free-running situation) is highly motivated. The level of excitement in the usual situations is so high that any "manners" taught in a handling context are thrown to the wind, so to speak. So in situations like this, the usual recommendation is management.

Some of the creative and perhaps safer methods to get your gelding out of the barn and into the pasture with other horses is to put a sturdy pipe round pen inside the pasture where the other horses are kept.

In many climates, a sixty-foot round pen paddock with a wind break, shade, hay, and water can be a nice alternative to an indoor stall. He could be outside and within sight of the herd a good deal of the time.

The chasing, herding, and mild sexual interest you describe are certainly within the normal range of gelding behavior when turned out to pasture, especially when first turned out with a new group. But one thing you might want to confirm is that your gelding is a true gelding.

Before you make major management changes or further consider behavior modification, you might wish to have a veterinarian examine Sass and do some blood hormone tests to explore the possibility of a retained testicle. If he has a remaining testicle (in the abdomen or inguinal area), removal of it and the resulting diminished male hormones is likely to result in an appreciable reduction of stallion-like behavior.

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.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More

Free Newsletters

Sign up for the latest in:

From our partners