Why would my older dog be foaming at the mouth when around my new puppy?

Answer by  tickledpinktwyce (16)

Foaming at the mouth for a dog is a natural reaction to stress and possible fear, in this case, of the puppy.

Answer by  morganrosengmailcom (13)

Humans sweat when they are nervouse, dogs foam at the mouth. Your dog is most likely nervous around the puppy. When this happends a dog creates more saliva creating a foaming appearance. It also happens when a dog is around food, hopefully your dog doesn't think it's food.