Good possibility that it's coyotes they're a lot easier to scare off by a herd than a cat is. Usually with coyotes you will have bites and lacerations on the defender cattle also. A cat may have very well decided to leave provided the other cattle had proven to be too much. I live in the foothills of south eastern colorado so I deal with bears, mountain cats, and coyotes. The best thing actually that I have found for a defense measure is a draft mule. Other than that contact your local division of wildlife and see what your laws are and what they suggest; here we can defend our stock by any means.