Even in Wisconsin, summer days can be hot enough to cause heat stress for cows. The thermo-neutral range for cattle, in which they do not need to expend energy to keep their body temperature stable, is about 41°F to 77°F. When the temperature is above 77°F, especially with high humidity, cattle can have reduced production, particularly if nighttime temperatures stay over 70˚F.

Managing heat stress in dry cows is just as important as it is for lactating cows because it determines the amount of productivity and success a cow will have during her lactation. It can also influence the future success of the daughters and granddaughters of the dry cow.

Hot weather can bring a long list of problems for dairy producers. When cows are heat stressed, they eat less, produce less milk, have reduced immune function and higher SCC, and show reduced fertility. A spike in lameness often follows the hot season. In severe heat waves, cows can even die. In addition to the economic burden, the discomfort from heat stress also reduces animal welfare. UW-Madison Extension provides information on cooling cows housed in barns, where they are shaded from gaining heat from direct sun exposure.

Heat stress occurs when an environment impacts the ability of a cow to get rid of body heat. Cows need to be raised in an environment where temperatures are within their thermoneutral zones to achieve their maximal genetic potential. Failures to establish adequate environmental temperatures can dramatically alter behavior, health, and productivity of cows.