Why is one of my dogs attacking the other?

Ever since she was brought home, she's always liked to mess with the boy, first by licking his face and chasing him around, but now that she's older, she full on attacks him, leaving chunks of hair on the floor. Examples of what seems to trigger this behaviour in the female are: Playing with toys: If the boy is playing with me, she attacks him. If she's playing with me, my poor boy better not get close or she attacks. Sitting next to people: When my boy is sitting next to me on the couch, she likes to jump up and get some pets, too. But sometimes she takes the boy's spot, and he has to move. Even when he does move out of the spot quick enough, she'll sometimes growl at him before trying to attack. Getting excited: When I come home, or if the two see animals outside, they head to the door to bark, and sometimes, my female, without warning, will just jump on top of the boy and start biting. She attacks almost daily. Sometimes more than once a day.

The most common reason why a dog is suddenly aggressive toward another dog from the same household is a dispute over one of three things: Possessions, Food, Space / Territory. All three can be managed provided the problem is addressed promptly. Aggression related to food or toys, aggression related to jealousy, aggression related to fear, and aggression related to space/territory can all be trigger points for sudden aggression. Intact male dogs tend to have more innate aggression than either female dogs or neutered males. Dogs are pack animals and the dynamic of the pack is established between dogs over a period of time. If aggression persists and you are unable to identify the trigger yourself, you should certainly seek the assistance of an experienced dog behavior expert. Underlying health concerns can often manifest as sudden changes in behavior, including aggression. Once any medical issues have been ruled out, get the view of a dog training expert who can help you deal with this stressful event.