Dietary changes improve milk production in heat-stressed cows

Rising temperatures pose major challenges to the dairy industry. For instance, the milk production of Holstein cattle can decline by 30 to 70 percent in hot weather. According to a research team from Cornell University, heat-stressed dairy cows often develop gut permeability (leaky gut), which contributes to a significant reduction in milk production. However, the experts found that milk production can be partially restored by feeding the cows organic acids and pure botanicals. 

“This has immediate application,” said study senior author Joseph McFadden, an associate professor of Dairy Cattle Biology at Cornell. “And we hope it serves as a catalyst for the field and ignites further research into dietary approaches.”

Climate change is already causing reduced milk production in Holsteins, the dominant dairy cattle breed in the United States. Even in the New York state, where the climate is generally cooler, these cows’ health and productivity are threatened, since they start experiencing heat stress at about 75 degrees Fahrenheit.

“In New York state, we’re projected to have an increase in heat-stress events in the next decade, but the precipitation is supposed to stay. With major droughts and water demands in other areas of the country, there may be an increased emphasis on maintaining the strength of the Northeast dairy industry, but we’ll still have more heat-stress events, and we have to be proactive and ready,” Professor McFadden urged.

Heat stress is causing the cows to eat less, and this reduced food intake accounts for 30 to 50 percent of the drop in milk production. According to McFadden and his team, the remaining decline develops due to an increase in intestinal permeability, which activates the immune system. “The general working hypothesis was that an activated immune system partitions energy away from milk production to support immune function,” he explained. 

“When the gut becomes permeable, it allows bacteria to enter the cow that activate the immune system and cause inflammation. But there had never been a study that directly confirmed that heat-stressed dairy cows developed leaky gut. Prior data only inferred this possibility.”

Fortunately, the scientists discovered that the consumption of organic acids and pure botanicals significantly reduces cows’ gut permeability and increases food intake and milk production, restoring up to three kilograms of milk per day. Moreover, cows kept on this diet showed increased nitrogen efficiency, thus reducing emissions of this harmful substance.

Further research is needed to assess the efficacy of different additives, and recommend changes to the staple diet of cows in the U.S. through optimization of the Cornell Net Carbohydrate and Protein System (a model used to determine what dairy and beef cattle should eat). “That model helps nutritionists formulate diets for cows. If we can improve that model and understand the nutrient requirements that a cow has during a heat-stress event, we can ensure she’s getting what she needs to maintain optimum health and performance,” McFadden concluded.

The study is published in the Journal of Dairy Science.   

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By Andrei Ionescu, Earth.com Staff Writer