Starch inclusion in the ration provides readily available digestible energy for dairy cattle. Of course the most common is corn grain, which is highly digestible but not as fermentable as other cereal grains.

“About 75% of the starch from corn is degraded in the rumen of cattle. Starch from barley, wheat, or oats ranges from 80% to 93% rumen degradability,” explained Ohio State’s Kirby Krogstad.

Why does that matter?

Starch digestibility in the rumen greatly affects the rumen’s delicate balance. If a feedstuff causes too much fermentability, the rumen pH is impacted and ruminal acidosis becomes a concern.

“If you’re switching grain sources, keep an eye on manure scores, milkfat percentage, milk urea nitrogen, and feed intakes to make sure you’re not running into rumen problems,” Krogstad suggested. “The use of technology like rumination collars or rumen boluses can monitor rumen pH and rumination times. If either are reduced when changing grains in the diet, you may want to adjust the ration.”

If ingredient balances on a farm suggest utilizing some of these highly fermentable grains, Krogstad recommended reducing the total dietary starch and increasing fiber digestibility accordingly.

One more factor

The reason that corn is less fermentable in the rumen is because of its vitreousness. “Vitreousness is the level of protein encapsulation of the starch within the grain,” Krogstad shared. “As the vitreousness of grain increases the rumen digestibility of the grain steadily decreases.”

This is closely associated with kernel density and the rate at which the starch breaks down in the rumen. More vitreous grains have a yellow and glassy appearance when the grain is dissected. More “floury” grains have a white and opaque appearance when dissected.

In all grain types there is some variability of fermentability. Krogstad recommended monitoring grain inclusion and cow behavior to identify these changes within the grains fed on farms.