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Healthy Pets

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What Makes an Aggressive Dog?

Study suggests it's not so much the breed as the gender, training, origin and owner's age


In breaking down factors associated with dog aggression, the researchers found much more than the dog's breed at work. For instance:

  • Dogs owned by people younger than 25 were nearly twice as likely to be aggressive than those owned by people older than 40.
  • Neutered male dogs were twice as likely to be aggressive as neutered female dogs. However, there was no significant difference in aggression risk between neutered and non-neutered males.
  • Dogs who attended puppy-training classes were about one and a half times less likely to be aggressive to strangers.
  • Dogs trained using punishment and negative reinforcement, however, were twice as likely to be aggressive to strangers and three times as likely to be aggressive to family members.
  • Dogs obtained from animal rescue and other sources were much more likely to be aggressive than those bought from a breeder.

"The origin of the dog was a significant factor in aggression toward family members," said Mary Burch, Canine Good Citizen director for the American Kennel Club. "There was a 2.6 times increased risk in dogs obtained from rescue centers, and a 1.8 times increased risk from a combined category of 'other' sources, including pet shops and Internet sites, as compared to those obtained directly from breeders."

A lot of dog aggression is spurred by fear and anxiety, Zawistowski said. To avoid having an aggressive dog, he said, owners should properly socialize their pups by doing the following:

  • Leaving puppies with their litter until 8 weeks old, so they learn how to be social with other dogs.
  • Taking them to puppy kindergarten classes before 16 weeks old, so they become comfortable with other people and dogs.
  • Engaging them in positive-reinforcement training that teaches them things such as not jumping on people or pulling on a leash.

Older dogs that suddenly become aggressive might be experiencing pain due to an ailment. "If you're looking at a 6- or 7-year-old dog that's starting to be aggressive, you might want to look at whether the dog is starting to have some arthritis," Zawistowski said.

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