i had bunjee neutered at about 4 months and a little over 4 lbs. he was just fine. if you don't trust the condition of the surgery room at your vet's then go somewhere else! having another vet do the neutering is definitely better than to leave your puppy to a surgery room of questionable state! try a local spca or even another local vet.
my understanding is that in puppies, testostrone will tell the body when it's reached its adult size and weight. so by removing the testicles on a male puppy, the body may have delayed reactions and continue to grow beyond its anticipated adult size. with an adult dog, since growth has been completed,this will have no effect and weight gain is just a myth.
imho, yorkies are so small anyways, i think my bunjee can use a little extra weight and size just to match his personality.
