Research Note

Heat Stress: Dietary Tweaks

Even mild heat stress can impact the performance of high-producing dairy cows. However, when the daily average temperature-humidity index (THI) approaches 70, they’re reaching a tipping point. A few more points and their dry matter intake can drop 20-30%.

Lower DMI presages a dangerous cascade — lower milk and milk component yields, higher somatic cell counts, and higher risk of sub-acute ruminal acidosis, leaky gut, systemic inflammation, etc.

What does recent research say about dietary interventions to combat heat stress?

“Given lower DMI,” says Cornell’s Dr. Joe McFadden, “the diet still must meet the cow’s energy demands, even as more dietary energy diverts from milk production to other physiological priorities under heat stress.”

McFadden notes data from an energy intake study done in a metabolic chamber (table). Heat stress reduced DMI and milk yield, which was not surprising, but it also reduced gross energy, digestible energy, metabolizable energy, and net energy for lactation.

Source: Personal communication from Dr. Joe McFadden

McFadden suggests a few “dietary tweaks” that can increase the diet’s energy density to compensate for the loss of DMI without knock-on risks of acidosis and increased gut permeability:

• Reducing fiber content and enhancing the inclusion of high quality, easily digestible forages, which have the potential to lower heat increment for digestion
• Supplemental fat (less than 6% on a dry matter basis), including rumen-protected unsaturated fats (calcium-salts and mixed prills)
• Rumen-protected methionine, rebalanced trace minerals and vitamins (including rumen-protected B vitamins), betaine (as methyl donor and osmolyte with potential to enhance fiber digestibility and gut barrier integrity), organic acids

Besides lower DMI, other factors contribute to reduced milk synthesis in heat-stressed cows. Heat stress appears to increase gastrointestinal permeability and activate the immune system, shifting nutrients away from the mammary gland. In this context, McFadden points to recent research that investigates supplemental organic acids (eg. citric, sorbic) and botanicals (eg. thymol, vanillin), fed to help restore energy corrected milk production in lactating cows under heat stress. The use of probiotics, zinc, choline, and omega-3 fatty acids are also considered nutritional therapies.

For more on nutritional research to combat heat stress, see our previous Research Note.

Questions?

Email FeedInsight 4Dairy