Those are good qestions to ask your vet, but from my owning dogs best to have them fixed and they actually will be longer lived and less chance of having medical problems in those reproductive areas later in life. NO! they will not get over weight unless they are inactive and you start over feeding. I am very certain with my respouce but a Vet can give you a better reply in Medical terms. I do know that it would have been better to have had it done before she had her first cycle. But still better then having it done after she has had her first litter!