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Hot Summer Days Can Reduce Appetite and Milk Production

By Lyle Rode, North American Technical Services Manager, Novus International

It’s a hot summer day, and your dairy cows just aren’t eating like normal. What can you do? Protect them by changing their diet.

When cows are heat stressed, they experience a reduced appetite. Heat stress research indicates about 50 percent of reduced productivity or milk yield is because of reduced feed intake. The other 50 percent is due to the direct physiological effects of being heat stressed, which goes back to the gut.

An important function of the gut is to be a barrier, preventing unwanted molecules that reside inside the gut from entering the animal's body. Envision the gut as a tube running from the animal's mouth to its anus. Inside that tube is a variety of unwanted molecules, pathogens, antigens, toxins, acids, etc. that are supposed to stay inside the tube and be discarded in manure. Because of the reduced blood flow to the intestine, the tube's barrier starts to become leaky or permeable, and these pathogens and other antigens have an opportunity to infiltrate into the cow’s body.

The immune system recognizes them as foreign, which initiates an intense immune response requiring a large amount of nutrients, specifically glucose and amino acids. Those nutrients are now going to be prioritized for the immune system rather than being used by the mammary gland to make milk. Consequently, milk yield goes down from the reduction in feed intake.

Effective nutrition strategies to combat feed intake due to heat stress include:

  • Maximize energy density in the diet
  • Increase the fat content of the diet
  • Feed more buffers, like bicarb, to minimize the rumen acidosis
  • Feed ionophores
  • Feed cows more potassium
  • Feed combination antioxidants like AGRADO® Plus to maintain oxidative balance

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