THERE IS A DRUG.
It is a 14 day treatment. It is not cheap. It will change a horse's personality during the treatment. It is best used at around 16-20 months ( depending on how mature your colt is) And given with turnout and work. The Testicle needs to be as close to the loop as possible for better results. Depending on the size of the other Testicle also has some effect on the success of the treatment. This is about a 60 percent success rate. My vet says lower. But studies said 60 % So Give or Take on the results.
When I was checking into this My everday vet had no idea.
A T-Bred vet, friend of mine said he would check into it. His son was in 4-H with my children,
I had to get the name from a breeder, He gave it to me, I contacted my Equine vet and we talked it over, Yes he knew about it. My horse was past the point of suggested age treatment. Plus, My vet still believed it was a trait that can be passed on. So we gelded him and he's a fun horse to own. But He was intended to be a breeding horse. So the moral of this story, look before you buy...
Now I know 7 Ceders made the post about the drug. So if any of you would like to know the name contact her as it was she that mention it to start with. Experience speaks volumes. After all isn't that why we are on this forum?