Post-nursing female dog behavior

What is normal behavior for a dog that gave birth about 2 months ago? I ask because I volunteer at the county dog pound and have been noticing a lot of momma dogs are euthanized for "aggression" after we adopt-out all of her puppies. It seems that we may be euthanizing dogs that would be fine if we just give them some socialization in a foster home for a few weeks. Is it a normal tendency to growl/snarl at humans when a momma dog has just been removed from her pups and put in a kennel?

Just looking for some folks that have breed a female dog and know what "normal" behavior is when the puppies are gone.

If the shelter you are working with is putting down a lot of bitches after getting the pups adopted I would guess that something is going wrong somewhere along the line.
I would suggest getting in touch with local breeders and asking advice, ask them to come to the shelter and have a look - stressing that it is a charity.

Any news?