age of strays

Question
have 2 stray lab puppies that we are feeding and want to have them spayed but don't know how old they are. can i estimate by weight?

Answer
I am afraid not.  Labs vary too much in size.  Better go by the teeth.  If they have small, uniform sized teeth, chances are they are less than 3 months.  If they have have large uniform teeth, they maybe 6 months or older.  If they seem to have a mixture of sizes, likely they are somewhere between.  They lose their front incisors first, then bicuspids, molars, and the nasty, sharp little puppy canines last.  The vet will make his own estimate.  I think the tendency is toward earlier and earlier spay/neutering.  On most medical questions, I go along with what my vet suggests.  

Thank you for being so responsible and taking in a couple of strays and having them spayed.  I get so upset with the constant stream of questions on breeding here from people without a clue.  So nice to have one from somebody part of the answer instead of the problem.  I will try to help with any other questions.  

My 11 month Nita is 47 pounds.  A couple of the Labs I have had were 70 pounds at that age.  She barely made 41 pounds in April allowing her to share the same package of Revolution as my older Lab.  My daughter has a 5 month old.  He is smaller than Nita, but stockier and may weigh as much. Both are carefully kept lean.