I found this on vampires feeding on vampires- interesting

We’ll have to make some assumptions. First, that vampire blood is more or less of a type (heyooo!) with human, such that it is nutritious. Second, since vampires always seem to be attached at some human’s neck, vampire blood is perhaps more concentrated in the elements vampires need. Think of it as how DDT gets more concentrated in animals further up the food chain.

So…

This leads me to believe that a vampire is the ideal snack for another vampire!

While a fellow vampire may be harder to hunt down and slurp on, its blood is more nutritious and (presumably) power-laden. So you will end up with a ghastly ladder of meta- and meta-meta-parasitism, with the oldest, fiercest vampires feeding exclusively on vampires who prey on other vampires.

Of course … this is kind of hard on the overall vamp population, and likely explains why vampires don’t, well … “take over”. The constant need to get powerful enough to fight off the meta-cannibal vampires causes all vampires to prey preferentially on their own kind. Belike they turn other vampires and rear them just to have a herd of “feeder-vamps” at their disposal.

So … forget the images the paranormal romances give you, of elegant vampire courts, and eerie bands of undead brothers. No. What you get instead is vampire factory farming, a ghastly, charnel mechanization which would make a hog farmer blanch. Row upon row of newly-turned vamps (“veal”, in their argot) chained in pens barely large enough to lie down in. Their only freedom of movement is the freedom to dip their faces into troughs of blood stolen from blood banks.

The last of the van Helsing line, hight Jim, was quoted in the press:

Hunt vampires? No way. There’s nothing I could do to them that they aren’t doing to each other ten times worse. I’m switching to werewolves.