Sorry for the wait! We really weren't sure about this one, so it took a bit - The Witch would be perfectly fine with supplying either packets or tablets for vampire characters to eat, just like how food is produced for others, but given that it's something of a unique staple, it probably tastes a little dull compared to the good stuff. It's probably chicken blood.

So, if they would prefer to seek out alternate sources, that's fine, though the punishment for killing someone would still apply if they drained too much.