beloved family dog showing new aggression to baby

Question
My husband and I have a 4 year old, female, lab mix who has always been the sweetest dog. We recently gave birth to our first baby and he is now crawling. When he was not mobile our dog had no problem with our son but now that he is mobile our sweet dog is not so sweet anymore. At first we thought it was just because she was being frightened but now we're not totally sure. Tonight our son (who is never left alone to crawl on the dog) mearly approached the dog, touched her foot and then the dog growled and mouthed the baby's arm. She didn't draw blood or even leave a mark but it really scares me. We love our dog but we can't afford to keep her if she is becoming aggressive towards our son. What should we do about it?

Answer
Your dog is exhibiting bite inhibition (for now) and may be simply trying to give the baby a "message" that she does not want to be approached.  Your dog's behavior is most likely fear based (she's unsure what this individual is and his sudden change in behavior may be alarming to her) but she needs to be evaluated in person by a professional in dog behavior.  There are remedies available and it's quite possible the situation can be successfully dealt with, but meanwhile you need to keep the baby away from the dog. Do this in a manner that doesn't punish the dog; while the baby is crawling around she can be put into a separate room with a soft bed and some special toys.  A full veterinary evaluation should also be done to rule out orthopedic problems (common in Labs and first generation mixes of that breed) or other condition that may be causing her distress.  It's not at all uncommon for dogs to be fearful of babies; this is a lack of socialization to children that age and the fact that infants, toddlers and very young children smell differently from adults and behave in ways that a dog can experience as alarming (crying, odd vocalizations that young children make, sudden movements, etc.)

You can call the veterinary college in your geographical area and ask for a referral to a certified applied animal behaviorist or check this site that I discovered, which supposedly checks educational and professional credentials and has certified behaviorists available across the US and in Europe.  Here is the link:
http://www.iaabc.org/