Are your chickens pecking each other or could it be a predator? Vent pecking can be something they do if overcrowded or bored from not getting outside to roam around. Also, what are you feeding? A balanced chicken feed, layer or flock raiser type feed is best, 16-20% protein. If a hen has a prolapse, the red tissue can attract pecking and cannibalism if not discovered soon. Can you describe your coop set up, how many birds, how much space? Are they locked up securely at night?