Vampire Dogs
Did you ever think of vampires as nutritionally challenged individuals living in an era without nutritional supplements?
What would a person, a count with wealth eat, if he was dieing of malnutrition?
Might a person who found that he could not digest solid food, switch to blood?
Cattle or horse blood makes more sense.
There is a tribe in Africa, said to only swallow, water, cows milk, and the blood of cattle - which they get from nicking a bull and catching the blood in a gourd, and then stemming the flow from the bull.
The bull doesn't die - he is 'milked' for blood.
Many people could not live on this diet, as they loose the ability to make the enzymes to digest milk after childhood.
But what if a person lost the ability to make other enzymes?
The yuck feeling that people usually get from the idea of eating other people, might be a form of self protection - it is not safe to eat your own species, because their diseases become your diseases.