Answer to why it is never to hot to cut (geld) a horse!! No one knew!! I was surprised!!
This is just good old country wisdom that makes such total practical sense.
What is the biggest problem when cutting a horse?? Scrotal Swelling. The more the horse moves the less swelling he will have. The more he stands around the worse the swelling will be. Horses are just like us. If it hurts we will try and avoid it. Two long incisions in your scrotum obviously hurts. Walking/moving will hurt. The horse will avoid moving to avoid hurting. Which will result in a VERY swollen scrotum.
The hotter it is, the more flies, gnats and every other kind of bug type critter there will be. The only thing that hurts worse than moving is standing still and having all the bugs feeding on the discharges from the scrotal incisions.
A fresh cut horse will be SO uncomfortable in hot weather! He will be continuously stomping his hind feet, switching his tail, taking off running to get away from all the bugs feeding on his scrotal incision discharges. He is moving every second of everyday until his incisions stop draining. The result of all this movement is very little scrotal swelling.
Cut this same horse in cold weather and since you have no bugs ol' horse is real happy to stand very still, do as little moving as possible. The end result will be additional vet bills due to having MAJOR scrotal swelling.