Dear Disgusted,
Yes, I’ve seen this behavior before, several times and although it is not common, it is certainly not that unusual. It is more likely a behavioral problem, not an issue of being ‘proud cut’ and it is likely that this horse was gelded later in life and learned how to breed mares before he was cut. Just like in dogs, gelding a horse does not unlearn behavior that has already been established.
Often when people see geldings display stallion-like behavior, they refer to him as being proud cut, and assume that something went wrong in the surgery and somehow part of the horse’s testicles were left in there. This is possible, but not probable. It is possible that a stallion only has one testicle descended at the time he is gelded (a cryptorchid) and that the vet assumes he only has one testicle and leaves the other testicle in there. But vets are pretty conscientious about this, so it rarely happens. Still, you should have this horse checked by a vet to make sure.
Removing the testicles only prevents the manufacture of semen. It does not preclude the horse getting an erection and/or displaying any of the other breeding behaviors of a stallion. You’ll see geldings get erections all the time, usually when they are day-dreaming (we can only guess about what), but most geldings have never learned or practiced real breeding behaviors so after they are gelded, they wouldn’t know what to do and don’t have the hormones prompting them to explore these behaviors.
As for your friend’s horse, it’s probably not as big a deal as they think it is. It’s likely that once he settles in and gets used to this new herd, most of these behaviors will disappear. He may still occasionally try to mount them when they are in heat, but the rest of the time things will seem pretty normal. One of my best-ever beginner school horses would occasionally mount and breed a mare—but he was the gentlest horse I ever had.
No horses, whether stallion, gelding or mare, should be allowed to display any kind of interest in each other or any herd behaviors once they are in-hand or being ridden. This should be met with the harshest correction and there should be a zero tolerance policy about fraternization. This is why breeding stallions can be shown and handled and ridden like regular horses. But what they do on their own time in the herd is up to them and there’s not much you can do about it.
If this horse is excessively aggressive to herd mates—geldings or mares—you can resolve this behavior with an electric training collar called the Vice Breaker. But if this gelding is otherwise a good ride and well-mannered when being handled and ridden, I wouldn’t worry too much about it—just cover your eyes when the mares are in heat.v
JG
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