My vet prefers to spay females that are more than 2 pounds age is not the driver. What I produce is around that size at 12-14 wks. Read the studies done by other vets with the same findings. As a breeder who incorporates this, it gives me comfort to know these studies have been done. Not only on puppies but kittens too.
http://www.cvm.uiuc.edu/ope/ivb/spay-neu.htm http://www.canismajor.com/dog/earlysn.html http://www.danesonline.com/earlyspayneuter.htm
This site said it all for me..these are experience shared by other breeders proving rumors of incontinece to be untrue. Surgery is a risk period. Age or size doesn't make it any more of a risk from what I've been told by my vet or from what I've read.
http://regaliapyrs.tripod.com/early_spay_neuter.htm
My vet by the way has done a spay on a 1.5 pound female Chi and it was succesful, that's the smallest she's spayed thus far..yet again, she recommends them to be 2 pounds at least.
By the way, I did do a search for complimations and all i found were assumptions..nothing proven by studies ..just occasional bad experiences..