Is This Aggressive or Territorial Dog Behavior Toward New Puppy?

by Heather

We have an 8-month-old Jack Russell terrier who is really pretty well mannered, until we brought home an 8-week-old puppy in from the same parents as our first one. He has tried to attack her so we have to pen her in the kitchen to watch them. On day 2 he is laying on the floor outside the pen watching her constantly.

I am not sure if he is warming up to her or keeping an eye on her. He is getting neutered tomorrow. Will that help at all with his nasty territorial behaviour? I don't know when to trust him again with her, she is so tiny and cannot defend herself yet and he seriously goes at her.


Vet Suggestions on Aggressive Dog Behavior Toward New Puppy

Hello Heather,

Neutering your male Jack Russell Terrier is a good first stop to addressing his behavior, but I don’t think it is going to solve all of your problems (and it will take a couple of weeks for his hormone levels to drop significantly). Talk to the veterinarian who has been working with your dog through his vaccination series, neuter, etc. He or she has probably developed a pretty good feel for his personality and is in the best position to make recommendations regarding how to improve his behavior.

You are right to be worried about your young puppy’s safety. The 8 month old could seriously injure her. While you are getting your male’s behavior sorted out, they should be physically separated. Keep the female in the crate while you are working/playing with the male and vice versa; and of course feed them separately. Hopefully with some time, your male will stop seeing the puppy as a threat (if that is indeed what is going on) and learn to relax in her presence. When his behavior improves, you should introduce them using a head collar and leash to control the male.

This gives you the option of safely pulling the male away should he begin to act aggressively.

Best of luck,

Jennifer Coates, DVM

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