Editor’s note: The following answer is provided by Randy Shaver, University of Wisconsin extension dairy nutritionist. It is excerpted from a presentation he made at the recent California Animal Nutrition Conference.

Q: Can a reduced-starch diet be fed to lower ration cost without compromising performance? How far can starch be reduced?

A: The optimum starch content of diets for lactating dairy cows is not well defined, but 25 percent starch (DM basis) has been suggested based on a review of published feeding trials (Staples, 2007). Shaver (2010) reported on surveys of high-producing commercial dairy herds performed in Wisconsin and Michigan with dietary starch concentrations averaging 27 percent and ranging from 25 percent to 30 percent (DM basis). Increased corn prices, however, have created great interest in the potential for feeding reduced-starch diets.

Results from short-term switchback dairy cattle feeding trials in the literature suggest that reduced-starch diets formulated by partially replacing corn grain with high-fiber, low-starch byproduct feedstuffs may be feasible (Shaver 2010). Partial replacement of corn grain with forage, i.e. corn silage, to reduce purchased feed costs is also of much interest and results in reduced-starch diets. Depending upon market prices for high-sugar ingredients, the partial replacement of corn starch with sugar may be another alternative for reducing feed cost also resulting in reduced-starch diets.

Longer-term continuous lactation feeding trials are more appropriate than short-term switchback trials for evaluating the effect of reducing dietary starch content on feed efficiency, body weight change and income over feed cost (IOFC), and several trials of this type that evaluated the aforementioned feedstuffs will be reviewed herein. Coincident with the interest in reduced-starch diets is a renewed focus on increasing the digestibility of starch by dairy cows. Another objective of this paper is to provide an update on some aspects of the starch digestibility topic.

Read more on reduced-starch diets.