By Kendra Waldenberger
UMN Extension Ag Intern
Dairy cows can be significantly affected by the summer heat. Cattle can experience heat stress in temperatures as low as 70°F with humidity over 65%. Heat stress occurs when the weather conditions influence the cow’s internal body temperature to rise above 101.5°F. Cows become uncomfortable when body temperatures increase, hindering them from reaching their full immune, reproductive, and production potential. Understanding the potential impacts heat stress has on dairy cows is critical to sustain cow comfort, maintain herd efficiency, health, and profitability.
High feed intake, rumination, and lactation are all processes that produce a lot of internal heat. When the weather is hot, a cow’s instinct is to eat less to decrease her body’s workload. Reducing feed intake will require less digestion, which in return will generate less heat. However, consuming less feed will result in a drop in milk production. In addition, when cows are hot, they tend to stand more to cool themselves. Excessive standing will also cause a decrease in production because they are not getting adequate rest to produce milk.
Heat stress can delay cows’ reproduction. Cows’ fertility begins to decrease when their body temperature reaches 102.2°F, resulting in getting cows pregnant in the summer months more challenging. In extreme cases, when a cow’s internal body temperature reaches 104°F during the first three days of conception, the embryo will not develop, losing a potential pregnancy.
Lactating dairy cows are not the only ones impacted. When dry cows experience heat stress anytime during their dry period, they will have less cell growth, a lower cell metabolism, and high udder cell death. Dry cows that experienced no heat stress will have higher quality colostrum and milk production than cows who did. Heat-stressed dry cows will have a weakened immune system and be more susceptible to diseases. Weakened immune systems are not strong enough to respond to dry cow vaccines, therefore making them ineffective and an economic loss for farmers.
Calves born to heat-stressed dams will experience lasting effects. Newborn calves will have a lower Immunoglobulin G (IgG) antibody absorption when compared to calves whose dams were cool during their dry period. Utero heat stress causes an accelerated gut closure in newborn calves, leaving an even smaller window of opportunity to absorb antibodies. Calves are born with no antibodies, which is why receiving good quality colostrum is important. The colostrum from their mom provides the calf with passive antibodies to build the calf’s immunity. If the dam has poor quality colostrum, they will not get the needed antibodies to be healthy and productive. In addition, calves born to heat-stressed cows will often have lower birth weights and weaning weights.
The summer heat has several negative impacts on dairy cows, but implementing management strategies to keep cows cool will help mitigate the effects. One of the most popular systems is fans. They provide a way to move air around the cows, increase evaporation, and minimize hot areas. Installing sprinkler systems to mist water on the cows will draw heat away from their body. In addition, cows need adequate ventilation, shade when they are outside, and 24-hour access to clean and cool water to drink. Providing a combination of these strategies will help keep dairy cows comfortable during the hot weather, minimize decreased milk production, and ensure a healthy and productive future generation of cows.