How long have you had the Shih Tzu puppy for? Sometimes it can take a week or two for an older dog to adjust to a new puppy...maybe the Shih Tzu puppy is biting the Yorkie while trying to start play...puppy teeth can hurt and my dogs will nip if Soleil tries to play too hard...maybe she is just scolding the puppy which is ok as long as it isnt a vicious attack which will injure the puppy...even mother dogs will scold their puppies with a nip or two..
Dawn |