Ensure cows have plenty of access to fresh and clean water. A high producing dairy cows is estimated to drink over 25 gallons of water per day. During heat stress, the increase in transpiration rates to aid in the heat dissipation result in an even greater need for hydration. During heat stress, high producing cows may drink as much as 30-35 gallons of water per day. Clean water tanks regularly to facilitate maximum water intake.
Attend to necessary dietary changes and adjustments during the hotter months of the year. It’s well documented that during heat stress, cows have reduced dry matter intake. In order to compensate for a lower feed intake, one of the most common nutritional strategies is to increase the energy density of diets. Supplementing diets with rumen bypass fat sources is a common strategy used to increase energy density.
TMR management. It’s common to observe an increase in the level of feed sorting by dairy cows during the summer months. Animals tend to sort feeds more frequently during the hotter months of the year in a strategy to intake more digestible feed ingredients, such as grains, to meet their energy demand. It is also at the intersection of heat and moisture that yeast and mold growth in TMRs increase. Therefore, it is very important to make sure cows are receiving the appropriate amount of feed evenly distributed throughout the day to reduce the chances of mold and yeast proliferation. Mold growth, and consequently their secondary metabolites (toxins), can be potentially harmful to cows, negatively impacting their performance. The addition of TMR “preservatives” and “savers” can be an effective strategy for controlling mold and yeast growth in TMRs when ambient temperatures are conducive to mold and yeast proliferation.
Supporting the cow’s immune system and gut integrity is key. Advances in research have been made to understand the overall impact of heat stress on a dairy cow. These findings have demonstrated that only about 50% of the drop in milk experienced during a heat wave can be explained by the corresponding drop in dry matter intake. Today it is well understood that the gastrointestinal tract of dairy cows is severely impacted during heat stress. Dr. Lance Baumgard and his team have shown that animals under heat stress develop what is known as “leaky gut,” which is an increase of the intestinal cells’ permeability. This increased permeability amplifies the probability of luminal content (including pathogens and toxins) infiltration into the bloodstream. This phenomenon increases the cow’s inflammatory status and could potentially lead to sepsis. These insults that occur in the gastrointestinal tract help explain the drop in milk production that is not fully explained by the drop in dry matter intake.
THI, also known as the “Temperature Humidity Index,” is a simple measurement that relates the compounding effects of humidity on increased ambient temperature. Because the cow can vaporize less moisture (natural or artificial) when humidity is high, the cow’s ability to dissipate heat is reduced. Thus, at a given temperature, as humidity increases, the THI increases as well. The higher the THI, the higher the likelihood for heat stress. Recent research has shown that high producing cows begin to succumb to heat stress at a THI of 68, much lower than previously thought.
Rumen buffering is important for rumen health, and the cow’s overall health and performance. Special attention should be devoted to this area, particularly during heat stress when there’s an increase in feed sorting, which favors grains. During heat stress, the cow’s acid-base balance in the blood is disturbed, which reduces production of bicarbonate and secretion of this buffer into the saliva. Water consumption may be inadequate, which reduces dilution of acid in the rumen. All of these contribute to a decline in rumen pH, leading to subacute rumen acidosis. Supplementing diets with sodium and potassium buffers is a proven practice that will help minimize fluctuations and declines in rumen pH.
Exercise caution when setting up feeding/milking schedules, prioritizing cow comfort during summer months. Modifying your feeding schedule to include
delivery of fresh feed during cooler times of the day may promote more dry matter intake. Feeding during cooler hours of the day may also promote more cow comfort since they will spend less time standing to eat during hottest hours of the day.
Science has made big advances in the area of heat stress mitigation, helping us understand some key changes in the animal’s metabolism when exposed to stress. In this article, we have briefly mentioned changes regarding “leaky gut” and an increase in inflammatory pathways as some of the key factors contributing to the decrease in production performance associated with heat stress. The use of feed additives to mitigate heat stress has been another focus area for the dairy industry. Some feed additives have been shown to help alleviate heat stress in lactating cows. A lot of attention has been placed on the use of live organisms and yeast products to help stimulate gut immunity and help strengthen the gut barrier. Another area of research has been with phytomolecules such as capsaicin. Capsaicin may help mitigate heat stress through vasodilation, improvements in feed eating patterns and water intake.
Stay ahead of the game. Be proactive and prepared for the setbacks that you may be faced with once the heat and humidity set in. Make sure heat dissipation equipment such as fans, soakers and misters are clean, well-maintained and working properly. A fresh, clean and plentiful supply of water is a must. It is essential to observe cow behavior, watching for signs of stress such as rapid respiration rates, prolonged standing and overall discomfort. Consider adopting revised feeding strategies such as changing feeding times, pushing up feed more frequently or incorporating feed technologies to aid in the mitigation of heat stress. These strategies should be implemented at least a few weeks prior to the first forecast THI day above the 68F threshold to better prepare cows for the upcoming season and avoid any unnecessary loss in performance and financial returns.
Editor’s Note: Gabriela Acetoze is a Ruminant Technical Manager at ADM Animal Nutrition. Her duties involve supporting customer sales, assisting and managing field trials, developing data to support sales of ADM Specialty Ingredients and providing internal and external technology trainings. Also, she works closely to the marketing, product management and research teams to help develop, manage and support sales efforts primarily in North America.
Gabriela received her doctorate degree in Animal Biology from University California, Davis where she studied the effects of different feeding strategies on mitochondrial efficiency and proton leak of Holstein dairy cows. She started her career as a National Account Manager for ADM Animal Nutrition, developing and straightening the sales of ADM Specialty Ingredients in California, Arizona and PNW.
A native from Brazil, she is an active member of American Dairy Science Association, Professional Animal Scientists (2020 President for CA ARPAS Chapter) and California Animal Nutrition Conference. She, her husband Bob and their son Benjamin live in Tulare, CA. Don Jaquette is a Dairy Nutritionist for ADM Animal Nutrition. His current responsibilities include Dairy Technical Team leader and dairy field support for the Mid-Atlantic region. He also oversees dairy technical training, ration formulation program support, and product and program development for domestic feed businesses. Don earned a MS and Ph.D. in Dairy Nutrition at North Carolina State University.
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