The NYT has an interesting article about P.Z.P., an immunocontraceptive that is used to control horse and deer populations in the United States:
Dr. Kirkpatrick has one view of why it is not more widely used. “The problem isn’t scientific, it’s political and cultural,” he said. “We’re dealing with a cowboy culture. One told me, ‘We don’t do it this way; we do it on horseback with ropes.’ ”