Shortii:
By all means get insurance on your cattle! Go to your farm policy agent and add the cows and calves to your policy. This will cover you for liability also. Sometimes cows get out in the road and hit by cars-- your farm liability policy will come into play there, but also if you have the cows listed you may be able to get the cow covered too. Most farm policies with livestock will only cover lightning, drowning, possibly accidental death- depends on your policy. I know that my policy would make me add an addenda for blizzard coverage-- cows buried in snow.
If you want a policy that covers each cow and calf that is dead no matter how they died-- you will probably have to buy a separate mortality policy from what I understand. Those can be quite expensive also from what I have investigated myself.