"It is well known cow comfort is essential for high milk production especially during periods of heat stress. Taking the time to focus on cow comfort aids such as additional fresh clean water, air movement, shade, evaporative cooling via sprinklers, while providing energy dense, palatable diets will help minimize lost milk production and reduced reproductive efficiency due to heat stress," Erickson said.
Heat Stress and the Diet
Heat is produced as a result of microbial fermentation in the rumen. Low quality, stemmy forages generate more heat of fermentation inside the animal, contributing to the animal's total heat load, explained Alvaro Garcia, SDSU Extension Agriculture & Natural Resource Program Director and Professor of Dairy Science.
"Heat is used to maintain body temperature when ambient temperatures are low (below 40 degrees Fahrenheit). However, when ambient temperatures are high the cow needs to maintain its body temperature within biological limits compatible with life," Garcia said.
He explained that the cow's options are limited. "She can drink more fresh water (water evaporation from the body dissipates heat). She can also look for cool spots like ponds, shade, and places with good air circulation, or she can decrease her dry matter intake," he said.
High quality forages are digested faster and result in less heat being produced. So, Garcia encourages dairy producers to consider enriching the ration whenever feed intake decreases due to heat stress.
Energy of particular concern, he explained, as most of it is derived from the fermentation of forages within the rumen. "Increasing energy density might require greater amounts of concentrate and/or byproducts," he said. "Keep in mind that shifting the grain/forage ratio may increase the risk of not having enough rumen "scratch factor" (effective fiber) to optimize rumination."
When the rumen mat formation is inadequate, saliva production decreases (less chewing activity). This, Garcia explained, decreases rumen pH and allows more grain to be fermented in the abomasum and intestines.
Adequate particle size and the use of buffers such as sodium bicarbonate are critical in these "hot rations" to minimize the risk of digestive disorders such as acidosis and displaced abomasum.
"Sweating aids in heat dissipation, and sodium and potassium are secreted in sweat. This is a problem particularly in high producing dairy cows, which eliminate more of these minerals in milk," Garcia said.
When environmental temperatures are above 68 degrees Fahrenheit, make sure that diets contain at least .25 pounds of white salt per cow per day. Plenty of fresh, high quality water should also be available. "Test it," Garcia said. "You don't want water already high in sodium. Alleviating heat stress in dairy cattle is a challenge in every South Dakota summer."
Maintaining optimum nutrient balances and providing highly palatable, digestible feeds and ample supplies of fresh, clean water, along with shade and ventilation, will go far towards keeping dairy cows comfortable and their milk production up.