Somethings eating the cows

Late one night you hear a blood curdling scream from the field. Its Farmer Brown's cows. You rush out there, farmer Brown is right behind you with his trusty shotgun. In the light of the farmer's flashlight you see a dead cow being dragged over the barbed wire fence, leaving bloody scraps of flesh behind it. The farmer raises his gun and fires once. The roar echos in the still night. A brief sound of running footsteps, big ones, then nothing. The cow has a broken neck, his head was spun around three sixty. Brown lends you his extra shotgun. Its a pump shotgun from 1965. The next night you hear the cows freaking out again and you rush out with the shotgun. You trip in the darkness and you blow your left hand off.