Oh yeah, it's a rare occurence but the wolves and lynxes will kill cows if they're hungry. This happens especially in spring. You can reduce this by building traps around the cow pens, so that hopefully the predators will be distracted and get caught in the trap. That's not a 100% solution but sometimes it works. I also leash some dogs so that they are in range of the cows, if a predator shows up the dogs will aggro on them and hopefully scare them away.