My new horse Bob (Nov. 20230) was sold below his value as he is herd aggressive and must be kept alone in a pasture. My vet said that his behavior is due to being used as a stud until his was 4, at which time he was gelded and trained under saddle. My vet, who has a large breeding operation, said the aggression in the pasture will never resolve. I have the room to keep him separate. He has his own 4 acres, a small woods, and a shed. He has horses on all four sides on the other side of the fence.
However, Bob has impeccable ground manners and is extremely well-mannered under saddle.
And someone pointed out to me, that all geldings were stallions at one time. I looked around on the web and found that many people have “late gelded” horses. The vast majority said there is never a problem. Some did site pasture aggression.
My point is that this is likely and hopefully a training issue. Gain control and respect on the ground, and that should translate to a better riding horse. John Lyon’s said: the horse you lead is the horse you ride.