Is milkfat depression the result of too much corn distillers grains in the diet, the cows’ reaction to a knee-jerk dietary change, or something else?

“There is a big concern in the industry about milkfat depression when you feed distillers grains,” Kononoff, associate professor of animal science at the University of Nebraska, said during a presentation last month at the American Dairy Science Association’s annual meeting in Phoenix.

“We did not observe a statistical effect,” Kononoff says of his own research involving diets containing up to 30 percent distillers grains. “In fact, what we observed is total yield of milk fat increased.”

Kononoff points to other recent articles from the Journal of Dairy Science that note similar observations.

“None of them show milkfat depression when you feed distillers grains to dairy cattle,” he says.

So, why is there a discrepancy between published research findings and what producers observe on farm? Kononoff believes one of the reasons is that treatment diets are specifically formulated to include distillers grains, but on-farm diets often include distillers on a whim, so-to-speak, when the price of corn goes up or the price of milk goes down. To accommodate the inclusion of distillers, people find themselves swapping one or two ingredients haphazardly, “and in those cases perhaps we see milkfat depression,” Kononoff says.

Another potential cause is rumen biohydrogenation. Rumen microorganisms are very powerful, he says, “and when we feed distillers grains, this is potentially something that is working against us.”

Biohydrogenation produces an array of conjugated linoleic acids (CLA) in the rumen. Even in small concentrations, some of them have been shown to have dramatic effects on milkfat.“There are really two big risk factors that can cause this cascade of milkfat depression,” Kononoff says.

  • Increased fat supply. In situations where you’re bringing a lot of distillers grains into the diet, you can drive up linoleic acid levels and contribute to milkfat depression.
  • Low rumen pH. Distillers grain is very fermentable, so if you’re not dropping dietary starch levels when you add it to the diet, you can run into low pH issues which put cows at risk for milkfat depression.

Click here to read abstract No. 338 from Kononoff’s presentation in Phoenix.