back40 has hot news on cool cows:
Cows are hot. Their eponymous rumens run at about 104F due to the furious activity of rumen biota. This means that heat is often a worse problem than cold since it takes energy to stay cool as well as warm, yet they need to eat and so refill the rumen to get energy. The hurrier they go the behinder they get. Shade in summer is as important as wind shelter in winter.
Not a lot of people know that.