Agreed with Paints 150%. You aren't the owner, you don't have any say-so in decisions like that. Last time I checked, in my state stallions aren't allowed to compete in 4-H anyway, although perhaps that varies from state to state. Perhaps a little heads up would have been nice as far as the date of the procedure, but the owner is by no means obligated to check in with lessees for their permission to geld a stud.
Wow, jeez, lots of posts in a short amount of time... I've gotta learn to type quicker... ;)