Total starch is a common measurement used when discussing dairy cow rations, but total starch levels only tell part of the story. It’s important to take a deeper dive into starch values, since cows respond directly to rumen degradable starch, which is different from total starch values.

Focusing on only the total starch content when evaluating feedstuffs in a cow’s diet will not provide all of the insights needed to understand how much starch will be available to the rumen microbes. As a result, animal performance may be affected.

Photo: Calibrate Technologies.

“Rumen degradable starch can be too much of a good thing or not enough of a good thing,” Dr. David Weakley, director of dairy forage research for Calibrate Technologies, said. “Without insights that provide an understanding of availability, both situations will negatively affect cow performance.”

Not an area to be overlooked, starch represents a substantial portion of the ration, ranging from as little as 20% to as much as 35%. Additionally, starch available to the rumen can vary across sources from less than 50% to more than 90% of the starch in certain ingredients.

This variation can be costly when not controlled and monitored, potentially leading to:

* Inconsistent milk production;

* Decreased forage digestibility;

* Over- or under-feeding cows, and

* Inconsistent milk components and feed intake.

“Starch digestibility levels can change suddenly as farms move through available feedstuffs, for many reasons, including harvest maturity, field locations and storage management. These sudden changes in the amount of rumen degradable starch in the ration can affect milk production, milk components and even cow health,” Weakley explained. “By proactively managing these variations, farms can maintain ration consistency for optimal performance.”

Testing for rumen degradable starch gives dairy producers and nutritionists more insight into how much starch will actually be available to a cow from any particular ingredient, allowing rations to be adjusted or optimized based on available feedstuffs. Routine testing every two weeks will provide insights for timely decisions, Weakley added.