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Help! My Unsocialized Stallion is Aggressive Toward All Horses!

Andalusian Stallion

Unfortunately, most stallions do not have the calm and sweet temperament as this Andalusian stallion. | Photo by Stephanie Davis

Handling stallions can take a lot of energy, and an experienced horseman. When you get one that has been isolated, it’s even more of a challenge. Horse trainer and natural horseman Bob Claymier answers a question about dealing with an agressive stallion.

Question: I just acquired a project horse – a 5-year-old stallion. He is easy to handle and well-mannered around people. BUT – he is EXTREMELY aggressive with other horses. To my knowledge, he was brought in as a yearling as a halter show prospect, and has had limited exposure to other horses since then.

To put it another way, he has lived a life of isolation. It appears that he knows nothing about normal horse social behavior, and he kicks and screams at other horses on sight.

It is truly frightening.


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I have dealt with a few stallions and have only seen this kind of species-specific aggression in individuals who were socially isolated. Of course, I do not have any concrete evidence to back this up, but I really feel that this has been a factor with this poor guy.

Since his arrival I have housed him next to my quiet older gelding, and they can touch each other through the grating in the wall. At first, the stallion tried to demolish the wall in an attempt to either breed or kill (or both? Thank goodness it was a strong wall!).

Over the last week (I have had him a week), though, he has slowly begun to improve. At least I no longer fear for the safety of my wall!

My plan for this horse is to geld him and make him into a riding horse. However, it would seem to me that some of his aggressive antisocial behavior is LEARNED.

Therefore, it would also be logical to assume that he will exhibit inappropriate behavior even as a gelding. I feel the best thing for him (after he is very much a gelding) is to be turned out with other horses to learn to be social again.
My questions for you:

Will group turnout help this horse? If so, HOW do I find a situation where he can be turned out with others, as I can’t imagine anyone will want to risk injury to resident horses during the initial phase?
Is there anything else that I can SAFELY do with this horse to help to transition him into accepting the presence of other horses?

Turnout with my other horse is not an option, as he is very arthritic and would likely be injured in the fray. I really appreciate your suggestions. My goal is to help this horse assume a more normal life. Thank you!

Bob Claymier’s Response: As a natural horsemanship breeder, this is a hot button topic of mine and one that I often get on a soap box about, so pardon me in advance.

In my Whispering Way™ Foundation Training Series: Complete Guide to Horse Breeding, Foaling and Foal Training, Featuring Bob Claymier DVD set, I start off the series at the very beginning by attempting to dissuade those who should never be involved in this activity at all, because so many unfortunate horses are produced as a result.

In my own breeding program, I am a stickler for attempting to re-create a natural herd environment for all of my offspring and particularly the colts.

This is admittedly a difficult situation to achieve, but I let my boys run with a herd for as long as possible (usually 1 ½ to 2 years of age depending on the hormonal development of the colt and the time of year) and then put them with pregnant mares for further socialization training.

There does have to be separation at some point, but by then herd instincts have been instilled and that is important because there is a limited window of opportunity for horse socialization to occur. As so often is the case, it sounds as if your boy was not afforded this early-on training and you are left to deal with a potentially very difficult situation and one that may not be easily correctable, if at all. Even if he were kept as a breeding stallion, the behavior you describe is not at all acceptable, as he would be dangerously out of control during that process as well.

Now to your specific situation: You did not mention the breed of the horse and whether he had actually been in a breeding program or simply an isolated show horse.

The only good news is that you report he is well mannered around people, is only five years old and has shown SOME improvement when stalled next to your gelding. I ask about breed because I have seen Arabians – as an example – that are more easily retrained in similar situations. I have also seen some remarkable changes in behavior once a stallion is gelded, but it is usually limited to those that have virtually never bred and are a young age to begin with.

I would immediately geld this guy (it is the correct time of year as well/Fall) and then begin to see what – if any – effect this has on his behavior some six to eight weeks (or longer) out.

It will take that long (or longer) for the testosterone to work out of his system. Like you, I fear that he now has some learned antisocial behaviors that may prevent him from ever being a truly normal horse, but only time will tell that.

Once gelded, you could begin to introduce him to other horses in a very controlled environment to see how he reacts. By that I mean things like stalling him next to other horses; putting him next to other horses across a fence while on a (long) controlled lead line; separating him and other horses by a tall, strong fence, etc., all to see what his reaction is.

There is also a hormonal drug given to mares to control their cycles that can be given to proud cut geldings and the like to affect their behavior, which might be beneficial during transitional training that you will be doing with him, and your vet can provide the product. His behavior in this environment will give you some clues on how next to proceed.

If he is still virtually out of control around other horses, then he likely will have to be isolated for the rest of his life and you will have to make a decision on whether that is acceptable in your situation. On the other hand, if there is improvement in his behavior, then you should be able to develop a gradual introduction program into a herd environment.

If he shows some degree of control, he could perhaps be turned out in a field where he could graze across the fence from other horses (be mindful that he might attempt to jump the fence, especially if mares were involved during their heat cycles).

If he were able to be ridden out safely with other horses while under control by an extremely experienced rider, then this would be another step in the right direction. If all of this was positive, I would likely select a herd leader mare – preferably draft in size – and put them in a controlled environment like a round pen. I would put a rope halter on the now-gelding with a LONG lead line – protect yourself with gloves and a helmet – and see how both react to each other.

There will come a time in this experiment where you have to be willing to remove the human element and let the horses sort it out for themselves. This obviously means there will still be risk involved regardless of the re-introduction techniques and training you have provided.

You will have to determine at this point whether you believe significant progress has been made and whether all involved are willing to take that necessary risk.

This may be a six month to a year exercise (or longer) but the fact that you are willing to take on this stallion project is a testament that good people still exist in the horse world.

You likely know the fate of this horse if you don’t try to turn him around and ultimately failing in this effort after giving it a good college try would be nothing to be ashamed about. I applaud your efforts, but do not envy the trials and tribulations that you will obviously be facing.

Keep us informed as to your progress and also let us know if we can be of any other assistance. Good luck!

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