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18 month Jack Russel getting aggressive
My sisters jack Russell is 18 months old and has been spayed. She has always been a very loving and warm natured dog.
For the past +- 1 month she has suddenly become aggressive in that she snarls and bares her teeth. She is not only doing this to the other dogs and cats that she grew up with, but is also snarling at my sister. She has not changed her food (Montego), nor her routine at feeding time. Is this aggressive behaviour normal for a jack Russell.
There have been no other animals bought into the family and no changes to our normal day to day routine.
Please can you give us any advise in this area. Many thanks in advance.