I prefer breeder vets (not alot of them but they do exist). They have a significantly different perspective than 'regular' vets on a variety of vet care topics. Mine is one of the top grey hound breeders in the country. Anyway her preference is after a first heat, though she certainly will do it earlier if requested and doesn't state it's a horrible thing (to do so earlier). I personally would wait, they aren't that big of a deal but you probably aren't going to go wrong either way.