Who or what kills Major de Spain's colt?

When Major de Spain's young colt is killed in the middle of the night, the hunters are perplexed and wonder if Old Ben might be behind it. Later, the young boy realizes it was Lion that killed the colt as he was held, cooped up in the training shed, totally deprived of food and water by Sam, who was trying to break the dog. Sure enough, when Lion comes into contact with the colt's remains, he lunges futilely at them.