I'd try not too, but if you're hunting herds, it'd be pretty difficult to determine if a cow had a calf or not...in the heat of the moment. From my perspective, if you're hunting cows, you're either killing a cow with a calf, a cow that is pregnant with a calf, or a cow that will have multiple calves throughout it's life. It sucks to leave a calf stranded with no mommy, but no other predators take that into consideration...in fact most of them would just assume kill the calf as well.