Labador temperment

Question
I have a 3 year old male chocolate lab who has been neutered (we got him from a rescue when he was 5 months old) and a 4 1/2 year old male pug who also is neutered.  They have always gotten along well, but as of the last two weeks the lab has attacked the pug quite aggressively the pug always has a hurt yelp/cry but no puncture wounds, I have only witnessed this 2 times.  Why would he all the sudden become so aggressive?

Answer
I don't see any obvious reason.  I would take both dogs to the vet for a check up.  It could be the Pug is sending aggressive messages you are missing.  It is also possible the Lab, now matured, is challenging the Pug for dominance.  Better leadership on your part might help.  

The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/ For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm