Rising temperatures pose major challenges to the dairy industry -- a Holstein's milk production can decline 30 to 70% in warm weather -- but a new Cornell University-led study has found a nutrition-based solution to restore milk production during heat-stress events, while also pinpointing the cause of the decline.
The study, published Aug. 2 in the Journal of Dairy Science, confirmed for the first time that heat-stressed dairy cows develop gut permeability, or leaky gut, which contributes to a reduction in milk production. Researchers also found that milk production can be partially restored by feeding the cows organic acids and pure botanicals.
"This has immediate application," said Joseph McFadden, associate professor of dairy cattle biology in the College of Agriculture and Life Sciences and senior author of the paper. "And we hope it serves as a catalyst for the field and ignites further research into dietary approaches."
The paper's first author is Ananda Fontoura, a doctoral student in McFadden's lab.
The research will help maintain the efficiency and sustainability of the dairy industry as demand and temperatures both rise. Climate change is already causing reduced production and threatened health in Holsteins, by far the dominant breed in U.S. dairy farming. McFadden said the New York state dairy industry is not safe because of its relatively cool climate -- heat stress in Holsteins begins to occur at 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," McFadden said. "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."
Heat stress causes the cows to eat less, and the drop in food intake accounts for 30 to 50% of the drop in milk production -- this 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 partitions energy away from milk production to support immune function," McFadden said. "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."
Researchers found that cows exposed to heat-stress conditions developed leaky gut quickly, after just three days. A control group in a thermal-neutral environment, with the same reduced food intake, experienced a delay in the development of enhanced gut permeability.
The study also found that the consumption of organic acids and pure botanicals reduced the cow's gut permeability and increased food intake and milk production, restoring about three kilograms of milk per day. The cows showed increased nitrogen efficiency as well, which can mean less nitrogen excreted into the environment.
Currently, sprinklers and fans are used to mitigate heat stress on cows, but these strategies burn fossil fuels and only restore about 60% of milk production. Economic losses due to heat-stressed dairy cows are estimated to exceed $1.5 billion a year, more than any other domestic animal production systems -- in large part because of the Holstein's intolerance for heat.
McFadden's team is working with surgeons at the College of Veterinary Medicine, who were able to isolate samples of the cow's intestine, and with colleagues in the College of Engineering and at Johns Hopkins University to analyze the microbiome and metabolite profile of the cow's GI tract. These studies will help determine why gut permeability occurs under heat stress and provide further insight into how to keep cows healthy.
"The field is really lacking in dietary approaches to improve gut health; it's an underdeveloped area," 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 precious samples. Cornell is really unique in that we have a lot of resources at our disposal to answer these questions."
Further research could reveal the efficacy of different additives, or even recommend changes to the staple diet of cows across the U.S., through optimization of the Cornell Net Carbohydrate and Protein System, a widely used model for determining what dairy and beef cattle should eat.
"That model helps nutritionists formulate diets for cows," McFadden said. "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."
This study was supported by a Northeast Sustainable Agriculture Research and Education Graduate Student Research Grant, the Foundation for Food and Agriculture Research (FFAR), and Vetagro S.p.A., a FFAR industry cosponsor. Fontoura is a FFAR Research Fellow.