Actually...... I watched a, I believe it was Judge Judy one day on this exact same scenerio... Lady driving to work on a backroad, was pretty dark, came over a hill and didn't see the cow and hit it... Did all sorts of damage to the front end of the car... The farmers were trying to make a point that they had a fence built not long before then and it was built to spec, so they should not be responsible... What it all boiled down to was that THE COW GOT OUT OF THE FENCE!! If the farmers can't keep the livestock contained, then you are legally responsible... Not sure what state it was in, or if the law is much different from state to state, but the farmers ended up having to pay for the damage to the woman's car...
Mark