I do not know where you have your information from, can only say that IME it is rare. Maybe it is different in US. Around here usually offerings are ale, corn, honey, cakes or the like.
As for whether it concerns humans as well as animals, again, that has no bearing on a topic on animal abuse. If people want to sacrifice their own blood or use it in a ritual, then that is their business and nothing to do with any kind of abuse.