Just joined, I am sorry for the dog, it must have hurt Like you know what, I run my dogs a lot for partridge. So Many options, may be a racoon, run some game cams in your area and build a data base of what's around.
The little guy took a whoopin. It might have been a small bear. A friend shot a bear when we were in New Brunswick I don't think it weighed 50 lbs. I picked it up with one hand to put it on the side by side atv. The outfitter said it was 1 1/2 years old.