Hi, According to those who have the most experience with neutered dogs (GDBA) bitches should have one season first, and dogs should be at least 10 months old.
Can you put me onto where I can find an article to this effect to pass on to puppy buyers, as some seem unconvinced when their vets are willing or encouraging them to have it done at 5 months or so! I consider this the same as having a five year old girl subjected to a Hysterectomy.
I only know this through talking to the staff at the GDBA breeding centre a couple of miles from here - I don't know where there's anything in print - sorry, Brainless.