I have 2 different litters of chihuahuas that were 7 pups each litter that the mothers killed all of the puppies and the 3rd litter she has 2/7 left.. That is so odd. I ha put Revolution on them before I knew they took. Could that have something to do with it? They delivere only a coupe of days apart. I can not think of anything else that it could be. Any ideas?