old dog learning new aggressive behavior

Question
A good friend who owns a 4 year old staffshire terrier had her first baby in January of 08 when she was living with her parents and their 2 dogs a pug mix and a boxer all three males.  Recently her and her partner bought a home and moved in with their new baby and their dog.  Then not soon after she bought a long awaited second dog, an English mastiff 8 month old female.  They have been in the house only 3 weeks with both the dogs and it has not been a smooth transition.  The older male dog is attacking the larger younger female with regularity.  The aggressive behavior has become so bad she has sent her older dog to her mothers house where he has no problems with aggression.  She does not see this as a solution but is not sure what to do at this point.  The 4 year old male has not had a history of aggression with dogs or people ever before and has always been a sweet passive boy but all the changes in his life have occurred so quickly lately.  What advice can you give to rectify the problem and ensure a safe environment for all involved, baby, mom, and both dogs?  Oh as well the female does not fight back or seem to initiate the fighting she exhibits passive behavior and has obviously become fearful of the older dog.  Please help.  Thank you for your time.

Answer
Is the puppy actually being injured? Sometimes an older dog teaching a pup manners can look pretty scary, but is all roaring and teeth, and no damage. Dogs understand it but humans are often alarmed by it. If it is just a toothy display, and the pup is accepting discipline, and uninjured, I'd try to keep the pup from bothering the older dog, but not be too concerned. If he is actually injuring the pup, certainly it would be good to get in-person professional help. If it's not that serious, I'd try some classical conditioning with the male if he doesn't have guarding issues over food - lots of cookies and attention when the youngster is in the room, and a bit of ignoring when she is not. That way, puppy's presence becomes the predictor of good stuff. In a household with a lot of changes, I'd also be giving the dogs as much routine and training as possible. Routine, and knowing what is expected makes dogs less anxious, and less anxious dogs are frequently less reactive. Sandy Case MEd CPDT www.positivelycanine.com