Hi, Im new to this site but could really do with some friendly advice. Ive a 3 year old neutered female Jack Russell and a 9 months old female Jack Russell puppy. They usually get along ok and have the odd fight usually food related but since Friday the puppy's behaviour has changed drastically. She has become so aggressive to the older dog they cannot be left alone, even when Ive broken up a fight you can actually see in her face she's just not going to give up. Where now into day three of this and are obviously very concerned. We've telephoned the vet for advice but we are still awaiting their call. Nothing has changed at home so we're wondering if this behaviour could relate to the pup perhaps being due to come into season?

Oh dear. As you say it could be that the pup is about to come into season but at nine months it is also the terrible teens (think Kevin - stroppy teenager) when they tend to start pushing their luck.

Perhaps your vet could recommend a behaviourist, who will visit your home and assess the situation and give you professional advice.

if your dogs are fighting over resources (food/toys/attention) take the resources away.

manage, separate, slowly introduce them together with food etc. tether one if necessary.

aggression should not make the other dog go away - or you are teaching a dog to use his aggression.

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I think a behaviourist is needed in this situation TBH. with regards to the food guarding (resource guarding) do you feed separately? What are they like with toys, their bed/s?