First of all, you'd have to catch the pig. Obviously once the pig finds out that you're a vampire, he's going to avoid you at all costs. On top of that, he can fly, which probably gives him quite a bit more mobility than you have.
Ellen suggests that the bat-transforming variety of vampire might be more inclined to attack a flying pig, but I see problems here, too. Number one, a bat is very small. It's doubtful that the quantity of blood a vampire might consume while in bat form would contain enough nourishment to sustain him for very long. The vampire would have to feed from the pig several times over the course of a day to get the same level of nourishment as if he were to attack in human form. If the vampire did attack in human form, the pig would probably be able to fly away, in which case the vampire's teeth would just rip out of the pig's flesh, or the vampire's teeth would come out and he'd be stuck with no fangs.
I guess the vampire could anticipate the takeoff and turn into a bat as soon as his fangs were in the pig, but that seems like an awful lot of work.