When puppies play, they teach each other how to control the pressure of their jaws so their teeth grasp their playmates without inflicting pain. In such cases, human intervention isn't required. But when puppies fight for real, it's a different matter, because those teeth become weapons.
Play Biting and Real Fighting
When puppies sink their needle-sharp teeth into each other, they can look as though they're trying to inflict serious damage. If this "mouthing" is accompanied by yelps, snarls, growls and bared teeth, it can be difficult to judge whether the combat is real or pretend, says Dr. Camille Ward, lead author of a study on how puppies play, published in "Animal Behaviour" in 2008. She suggests watching their body language for the signals dogs use to communicate playful intentions to each other. For instance, rolling on their backs to offer playmates a temporary competitive advantage is a "self-handicap" signal -- dogs would never voluntarily assume such a position of vulnerability in a real fight. Another signal is the "play bow," seen when a puppy puts his front end on the ground with his rear end in the air, often with tail wagging.
Sibling Rivalry Can Be Deadly Serious
People who adopt two puppies at once, either from the same or different litters, can be setting up themselves and the dogs for "the worst of both worlds," says U.K. dog trainer Stan Rawlinson. In "litter mate syndrome, also known as "sibling rivalry," two pups become rivals for the position of top dog in the household. When they squabble, owners inadvertently can exacerbate tensions by rushing to protect the pup they perceive as weaker from being bullied. This only serves to increase the resentment of the stronger dog while giving the other the impression that as the clear favorite, he should be dominant. There's nothing playful about these fights, which can end with one dog killing the other, Rawlinson warns.
Breaking Up Can Be Hard to Do
When potential for injury is involved, "under no circumstances should dogs be allowed to 'fight it out,'" say veterinarians Debra Horwitz and Gary Landsberg of University Animal Hospital in Tempe, Arizona. If both are on leash, pull them apart. If not, never try to intervene manually by grabbing a dog's collar or trying to pick him up because in doing so, you could be injured, either accidentally or by redirecting aggression onto yourself. Never forget how razor-sharp puppy teeth are. Distract the dogs by squirting or pouring water on them, spritzing them with citronella or trying to put a barrier such as a broom between them. Examine them for injuries. If they have injuries, take them to your vet.
Gain Control, Then Restrain
If you've been an overly permissive pup parent, crackdown time has arrived. From now on, regardless of the issues your puppies have with each other, both must acknowledge you as the "alpha" whose commands are law. After you've put an end to the fight, the next step is gaining control over the part of the body capable of inflicting the most damage -- the mouth. In extreme cases, you might need to muzzle the dogs, say Horwitz and Landsberg, but they should certainly be put on leash so you can take quick control in case of future hostilities. To force a dog into a subordinate posture, look him in the eyes and pull his head sideways so he can't stare back. Whenever you're not home to supervise, your dogs should be crated or put in separate rooms.
Your Vet Is a Resource
Experts may differ on the best ways to handle intractable aggression in puppies but all agree that it can't be allowed to continue. As dogs mature, aggressive behavior patterns become ingrained, making them even more difficult to change, says Ohio State University's College of Veterinary Medicine. Discuss the situation with your vet, who can advise you on a course of action. One possible route she might suggest: Hiring an animal behaviorist or trainer experienced in aggression management to work with you and your pugnacious puppies in your home.
Supporting the Dominant Dog
With pups, Rawlinson advocates strict separation, not only in different parts of the home but also in activities such as walking, feeding, playing and training, until they reach the age of 12 to 14 months. Horwitz and Landsberg recommend trying another approach first -- "supporting" the dominant dog in hopes of encouraging the subordinate to accept the status quo. Feed the top dog first, let him take the lead in going in and out, and greet and pet him before the other. If the top dog challenges the underdog to another fight, and he acknowledges dominance by assuming a subordinate position, owners shouldn't interfere as long as the aggression ceases, the University Animal Hospital vets say.
If All Else Fails...
Aggression between dogs living in the same household is extremely difficult to treat and if everything you've tried has failed, Rawlinson, Horwitz and Landsberg concur that for the good of both dogs and humans, one pup should be rehomed.