We have castrated our own horses for about 40 years. We have never had an infection or a bleeder. I have a very good set of emasculators and have never had a problem with yearlings up to 10 and 12 year old studs. We lay them down and have never had a problem with a single one of them.
After my arthritis got bad, I lost my dexterity and nearly cut my arm off, so I had the Vet out to do 4 or 5 of them. One nearly bled to death and one got so infected I had to open him up twice. He was so bad, we had to lay him down the second time and completely open him up and enlarge the original incision. She did not open him up far enough the first time and he closed over.
After that, I made a deal with a cowboy that lives 1/2 miles from us. I furnish the sterilized emasculators, the 'know-how' and a sharp sterile knife and he helps us do it. We do any he has art the same time. We have done this for about 6 or 7 years now. I repeat -- we have never had one infected, proud cut or injured in any way.
Horses are livestock. Like cattle and other livestock, they handle just fine working them like other livestock. We lay them down and never have a problem with that, either. It is all in knowing what you are doing.
I learned to do this and other surgical procedures when I lived 75 miles or farther from my Vet. All I can say, if you want to use a Vet for everything, that is your business. If we, or other ranchers, do not need one for everything, that is ours. I use Vets for many things but routine things like castrations is just not one of them.