That was no doubt a dog attack! I have seen it too many times unfortunitally. A cyote would have taken off the body and you wouldn't have found that carcus. It would have eaten everything. I have seen dog attacks on turkeys that looked the exact same with the breast eaten. I would get a great pyrenees or other LSG dog. They are worth their weight in gold. After I got a pyrenees, I only ever lost 1 guinea to a hawk but the dog never let the hawk have its kill. The dog never let it happen again and the hawk moved down the road and started killing my neighbors birds. I lost my dog 3 weeks ago today and have lost 2 Toms since he has been gone. I have 2 new pups that can't grow fast enough for me. Sorry for your loss and the dogs will be back. If you have access to a large live trap, put it in the pen on the other side of the opening and wire it to the fence where there is no other way in. Stick a chicken in the pen for live bait and wait for the dog to return. If you dont have a trap then call your county and se if they will provide one. Even in most rural areas they do have some kind of animal controll and have a trap to lend.