i dont think it is the farmers fault.
now it seems to me that a cow is a slow moving animal. i have never heard of a cow setting a land speed record. i would seriously question what your grand dad was doing before he hit the cow. if he was paying any attention at all he would have seen the very large patchy black and white road ahead. i dont see how, if he was traveling at the posted speed limits, not see the cow. your grand dad is responsible on this one. just a thought or 3.