Nutritional solution may help heat-stressed cows as US heats up

Rising temperatures pose major challenges for the dairy industry – a Holstein’s milk yield can decline by 30 to 70% in hot weather – but a new study led by Cornell University has found a diet-based answer to restoring the output of milk during thermal stress events, while identifying the cause of decline.

The study, published August 2 in the Journal of Dairy Science, has confirmed for the first time that heat-stressed dairy cows develop leaky gut, or leaky gut, which contributes to reduced milk production. Researchers have also found that milk production can be partially restored by feeding cows organic acids and pure plants.

“This has immediate application,” said Joseph McFadden, associate professor of dairy cattle biology at the College of Agriculture and Life Sciences and lead author of the paper. “And we hope it will serve as a catalyst for the field and spark new research on dietary approaches.”

The first author of the paper is Ananda Fontoura, a student at PhD in McFadden’s lab.

Research will help maintain the efficiency and sustainability of the dairy industry as demand and temperatures increase. Climate change is already causing reduced production and threatened health in Holsteins, by far the dominant breed in US dairy farming. McFadden said New York State’s dairy industry is unsafe due to its relatively cool climate – heat stress in Holsteins starts to occur at 75 degrees Fahrenheit.

“In New York State, we expect thermal stress events to increase over the next decade, but precipitation is expected to remain” , McFadden said. “With major droughts and water demands in other parts of the country, there may be more focus on keeping the North East dairy industry strong, but we will have even more events from heat strain, and we have to be proactive and ready.”

Heat strain causes cows to eat less and lower feed ration explains 30 to 30 % of the decline in dairy production, it was known. The researchers provided evidence that the remaining decline develops with an increase in intestinal permeability, which activates the immune system.

“The general working hypothesis was that an activated immune system separates energy from milk production to support immune function,” McFadden said. “When the gut becomes permeable it allows bacteria to enter the cow which activates the immune system and causes irritation. But no study has ever directly confirmed that heat-stressed dairy cows developed leaky gut. Past data has only inferred this possibility. ”

Researchers found that cows exposed to thermal stress conditions developed leaky gut rapidly, after just three days. A control group in a heat-neutral environment, with the same reduced food intake, experienced a delay in the development of improved intestinal permeability.

The study also found that consumption of organic acids and pure plants reduced the cow’s intestinal permeability and increased feed intake and milk production, restoring about three kilograms of milk per day. Cows have also shown increased nitrogen efficiency, which may mean less nitrogen excreted into the environment.

Currently, sprinklers and fans are used to reduce heat stress in cows, but these strategies burn fossil fuels and only restore about 60% of milk production. Economic losses from heat-stressed dairy cows are estimated at more than $1.5 billion per year, more than any other domestic animal production system, largely due to Holstein intolerance to heat.

McFadden’s team is working with surgeons at the College of Veterinary Medicine, who were able to isolate samples from the cow’s intestine, and with colleagues from the College of Engineering and Johns Hopkins University to analyze the microbiome and metabolite profile of the cow gastrointestinal tract. These studies will help determine why leaky gut occurs under heat stress and provide additional information on how to keep cows healthy.

“The field is sorely lacking in dietary approaches to improving gut health it’s an underdeveloped field,” McFadden said. “It’s very difficult to study because you need the facilities to do the heat stress studies and the surgeons to get those valuable samples. Cornell is truly one of a kind in that we have a lot of resources at our disposal to answer these questions.”

Further research may reveal the effectiveness of different additives, or even recommend changes to the base diet of cows in the United States, through optimization of the Cornell Web Carbohydrate and Protein Technique, a model widely used to determine what dairy and beef cattle should eat.

“This model helps nutritionists formulate diets for cows,” McFadden said. “If we can improve on this model and understand a cow’s nutrient needs during a heat stress event, we can ensure she gets what she needs to maintain optimal health and performance.”

This study was supported by a Northeast Sustainable Agriculture Research and Education Graduate Student Research Award, the Foundation for Food Research and Agriculture (FFAR) and Vetagro SpA, an FFAR industry co-sponsor. Fontoura is a FFAR researcher.

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