3 month old JRT attacked sibling pup any ideas why?

[HeffalumpsnWoozles]

We have 2 female JRT's same parents different litters eldest is 10 months who are best of friends. A friend of mine had a little boy from the most recent litter & he came to stay with me for a few hours today. All was going well for the first hour, playing great together.

Then all hell broke loose and my youngest female attacked her brother, it was vicious. Bared teeth, aggressive growling and trying to tear lumps out of the poor boy. Luckily he wasn't injured or phased by it at all & carried on playing with our older girl.

Was it jealousy? Is she going to be aggressive with other dogs that invade her territory? I'm shocked at how aggressive she was, owned JR's for the last 25 years and have never experienced this. She is well socialised, could it be a littermate thing? Although they've been apart for 4 weeks? Does she hate male dogs? Can anyone shed any light?

IME that's quite normal litter mate play. If it had been anything else, the boy would not have been unphased by it.

Litter mates are breathtakingly rough with each other - my litters get together every now and then and until they're about 2, their play with each other is entirely different to their play with anyone else. It's a sibling thing.

Obviously it isn't desirable - not least because it increases the chance of an accidental injury but it's not much to worry about either. I separate them when it gets too rough and give them a ticking off but leave them to it until that point.

As long as they're both going back for more, it's a game. But like all games, I worry they might end in tears so separate if necessary.

At 12 weeks it can only be play - even if it's a bit inappropriate.

Thanks Daisy, she was growling, snarling and frenziedly really biting him. As soon as I separated her from him she was trying to get back down to finish the job. Fingers crossed it is just the fact they're litter mates. I was really surprised as the older girl had been back to visit her siblings and parents with no trouble at all. Definitely a first for me to see one so young looking like she was going in for the kill!

is there really only 7 months between the two litters? That seems a bit harsh for the poor mother - how many litters will she have over her lifetime???

I was thinking the same thing as basildonbond that's too many litters for poor old mum!

Had exact same thought, poor mum.

Not here to argue the point about the mother who incidentally was spayed 2 weeks ago, her owner was always going to have 2 litters (she isn't a backyard breeder) and did all that she could to prevent the pregnancy. Separated the parents, bought protective nappy style pads when they were walked together and even made a onesie style affair for her male dog but they still managed to get together.

She admits herself it wasn't great but the mum was under the vets care the whole way through and is/was fit and healthy.

If you have concerns over the pups temperament speak to the breeder. Any reputable professional breeder will be very knowledgable about the breed and especially their own pups. They will give you ongoing advice and support if you have any worries.