Ive got a 1x collie grey, he is 18 months 24in 58lb. He is great with people, and ok with dogs, but he as just started to feel is feet, when other males come by him. I think its a age thing with them, as long as they are friendly he will be. Regards your dog, he might be trying to get the[ first] one in.?? With colliexs there are clever, and he aint forget what the other dog did. Keep him on the lead when males are about, and if he goes for them bollox him. With my dog, he is as soft as shit,But he is Strong+fast and could do alot of damage to most breeds of dogs. All lurchers know how to kill