Worldwide, beef cattle are generally reared outdoors with consequent exposure to natural conditions and are only maintained in housing systems to a limited extent. Beef cattle are particularly vulnerable not only to extreme environmental conditions, but also rapid changes in these conditions. In particular, fatter cattle (fat under the skin provides an insulation layer trapping heat inside the animal), cattle with a heavier hair coat (more insulation) and darker coated animals (black and dark red cattle) are very sensitive to heat.