I purchased my horse a year ago knowing he had some aggression problems. He is great around people, just not around other horses. Unfortunately, when he attacks, he goes for the throat just behind the jaw line. He refuses to let go at times, causing severe swelling. It's odd he doesn't kick or bite anywhere else. I keep him at a private facility where he is kept alone due to his aggression. Observing him now, he creates these huge poop mounds; his paddock is clean while he goes to the bathroom in only three huge piles.

We have never seen such behavior. Are these normal signs of a stallion? Could he be a cryptorchid (horse with retained testicular tissue)? He was bought at an auction so I have no history on him. I do know of a pony that was a stallion for years and then gelded. After gelding, he got quite aggressive. I don't know where else to look for information on aggressive horses.

Thank you for your questions. In your very short note, you have raised several interesting topics and good points about gelding behavior. To address all of them specifically for your horse, a better understanding of the specific details and circumstances would be required. It would also be helpful to have more specific information on the social groupings in which you have seen the behavior occur–for example, to know how long had your horse been with horses before the aggression occurred and how long it continued, and whether the herdmates and the targets of the aggression were mares or geldings. But with the information you have provided, I can make a few comments that might be useful to you and other readers faced with similar problem aggressive behavior.

It sounds like one of your thoughts is that your horse's aggression represents residual stallion-like behavior. Grasping and holding onto other horses is a natural element of stallion harem formation and maintenance behavior. It is seen in stallions when they are gathering a harem or trying to get a mare to stay with the group. This grasping behavior is also a conspicuous element of play behavior among juveniles, as well as the more serious sparring behavior among bachelor stallions. The grasp is typically onto the crest of the neck and mane, but can be at the throat or jugular area. So if the targets are mares, perhaps your horse's behavior represents stallion-like harem formation behavior. If the targets are other geldings, perhaps it represents inter-male sparring typical of bachelor stallions. Many true geldings retain this and other stallion-like behaviors, so it is difficult to differentiate a retained testicle or other exposure to androgens (male sexual hormones) on the basis of this behavior alone