A friend of mine has a female rescued GSD who is approx. 12 months old. She recently ran on ahead on a walk & when my friend caught up with her dog she found to her jaws wrapped around the thigh/rump area of another dog (of similar height but lighter) & would not let go. My friend eventually released her jaws from the other poor dog to find quite a lot of tissue damage & blood. My friend is distraught.

The dogs previous history is sketchy however some degree of mistreatment is known.

The bitch is unspayed & has only ever previously barked & growled at other dogs. I do not know if the dog she attacked was male or female or what led up to this attack.

Can anyone shed any light on this behaviour & can anything be done to help as my friend feels she cannot trust her dog now.

Can't say why the dog should be as she is, could just be bad breeding. But would suggest the dog is walked on the lead or muzzled or both. She may well be happier in a muzzle don't know why but it often calms a dog.

Then your friend could ask an APDT trainer to call and see if they can come up with a suggestion. Sorry it is not possible to sort aggressive behaviour on the web as one needs to see the dog and it's general behaviour, it is therefore not safe to try and help by proxy.

I agree 100% with Jackie, there can be so many other things going on that the owner may not notice of be aware of, it really needs an experienced eye and perhaps a referral from a vet (which is often covered by insurance BTW)