From this story on Slate:
Do livestock intentionally kill their owners? Yes. Cattle kill approximately 22 Americans per year nationwide, and the animals deliberately attack their victims in 75 percent of those cases, according to a 2009 study. About one-third of bovine killers have a history of aggressive behavior. Swine likely kill fewer people than cattle do, but there are no reliable data on this question. The CDC's mortality statistics group together all mammal attacks apart from those perpetrated by rodents, dogs, and humans. The death count in the mammal-attack category averages about 73 per year, including cattle-related mortalities.