Severe heat stress can reduce intake and milk production of dairy cows by more than a 25%, according to South Dakota State University dairy specialist Alvaro Garcia.
Garcia suggests the following to reduce heat stress in dairy cattle:
1.Provide an ample supply of fresh water. Water requirements parallel the increase in ambient temperature. As temperature goes from 86 to 95 F, water intake increases from 21 to 32 gallons. If cows have access to an outside lot, it is very important that the water be close to the shade and feed bunk. Higher producing cows are more prone to suffer from heat stress because they generate more heat as a result of their higher feed intake, and will thus require more drinking water.
2.Provide a comfortable environment in the holding pen. This can be done by a combination of air movement (fans), and water or shade if it is outside. Sprinkling the cows lightly can worsen the situation by creating a hot and humid environment that will not allow for heat dissipation. Increasing airflow can take care of this problem. If you are using water to cool-off the cows, try always to keep the udders dry to decrease the incidence of mastitis.
Shading from direct sunlight allows for a more comfortable environment. Research data however is limited as to the benefit of shade. In one study in Arizona, shade improved milk production by 7.5 percent when placed over the feed bunk as compared to a control situation with no shade. Permanent shades can sometimes be a problem as it might concentrate moisture and manure and might increase the incidence of mastitis.
3.Provide shade around the feed bunk. A covered feed manger provides shade so cows are more comfortable when eating. Shade cloth that provides at least 80 percent shade, can be used for these purposes.
For many producers, it works best to have a sprinkler system spraying away from the feed manger and towards the cows. Fans are then used to dissipate the heat from the cow by evaporative cooling of the water on the animal, as in the holding pen. It is important that water be sprayed away from the feed so that the feed does not get wet. It also is important that water does not reach the udder to prevent an increase in the incidence of somatic cell counts and/or mastitis. The area should also have suitable flooring to minimize slipping.
4. Dietary management. Whenever feed intake decreases due to heat stress, nutrient concentration should increase to maintain adequate intake of all required nutrients. Low quality, stemmy forages generate more heat of fermentation inside the rumen. High quality forages are digested faster and result in less heat being produced, Garcia said.
Increasing the energy density might entail the use of greater amounts of concentrate and/or by-products. Care should be taken to balance diets properly in order to avoid digestive disorders such as acidosis and displaced abomasums.
Garcia's publication is available at agbiopubs.sdstate.edu/articles/ExEx4024.pdf.