Dr. Dwight Roseler, Adjunct Professor Department of Animal Sciences and Purina Midwest Dairy Nutrition Consultant
Summertime brings thoughts of ice cream and baseball. The post-game little league event brings both teams to the local ice cream store to enjoy a refreshing ice cream cone. Dairy cows do not play baseball, but they do work hard and expend a lot of energy producing high quality, nutritious milk. A dairy farmer is a coach to their cows, as a dairy manager provides the proper resources to allow their cows to win during the summer.
Summertime heat brings serious consequences to dairy cows. The visible signs of summer heat to dairy cows can be one or a combination of the following signs in your cows: lower feed intake, higher respiration rates, more standing and less chewing, variable manure consistency, higher somatic cell count, and lower milk components. The invisible signs of summer heat stress which occur inside the cow include lower rumen pH, increased body temperature, lower immunity, leaky intestines, and lower blood glucose.
A good on-farm method to evaluate heat stress for your dairy herd is to monitor respiration rate. It will only take 5 minutes per day. Quietly walk into your dairy cow barn late afternoon and observe cows when no other feeding, milking, or manure scraping activities are occurring. Count respirations for 30 seconds on 10 individual cows. Double that number to get respirations per minute. Average respirations above 40 to 50 are evident of heat stress. Respirations above 60 indicate mild heat stress, above 80 moderate heat stress, and over 100 severe heat stress. Cows with pneumonia, mastitis, or are sick can have higher respirations due to sickness.
Peak milk production on early lactation cows is affected more by summer heat than a late lactation cow. Summer slump is evident in early autumn when cows that calved in June and July were supposed to achieve their peak production. These mid-summer calving cows do not achieve peak milk because summer heat lowered their peak milk which leads to the entire herd not performing well in early autumn.
What can you do to reduce the effect of summer heat on your dairy cows? Lactating dairy cow’s optimal environmental temperature is 40 to 60°F. Heat stress is a product of both temperature and humidity. The midwest has high humidity many days, thus fans need to be turned on when temperatures will be above 68°F during the day. Four to six mile per hour air must flow over the cow lying in a stall. Water sprinklers improve the effectiveness of heat removal from the dairy cow’s body. Remember the hot summer days when you stepped out of the pool, you feel cool. That is the same benefit cows gain by intermittently being sprinkled with water.
Nutritional interventions and additives can be put in place to reduce the effects of heat stress. However, if fans and sprinklers are not installed or properly operating, nutritional interventions will have little impact.
Consult with the online resources listed below for additional information on environmental and housing interventions to implement to help coach your dairy cows to a successful summer.
Heat abatement strategies for dairy cows.