That sounds like they might have used an uncommon (& inhumane) method of killing the rats? Or else the rats were allowed to fight each other? I can't think of any good reason for feeders to have holes in their necks. And no, I've never heard anyone say they've gotten rodents that way before. The loss of blood is a loss of some of the nutrition, but it won't hurt to feed it anyway- though personally I'd find a different supplier & also let them know why. I wonder what they'll say about it if you ask?