ive found that dogs see weekness in other dogs and will attack as there canine comrades are vulnerable in changes ...........same as wild pack animals , and hounds in kennels . any change in a dog , injury or coming into season , I may be wrong but im not far off that I believe the changes are led too weeekness which provokes attacks , maybe later on in a dogs life they are that much weeker , you always here they been fine for years , and that's why hot bitches hounds are kept separate from other bitches in hunt kennels, wolfs kill the weak in packs , sustain natural healthy pack ,........ na