Cows and pigs mingle regularly. However, when times are hard and groceries are scarce, pigs will become active predators. I've seen two boars bring down a calf. Pigs regularly prey on goats and sheep during "lambing season".

A fenced waterhole will never keep the pigs out. All of this just gives you more reason whack a few on a regular basis. Sounds like you have a nice private shooting hole.

Geoff