Balancing Carbohydrate Sources for Dairy Cows during a Period of High Corn Prices

 Carbohydrates, NDF and NFC, comprise about 70% of DM in diets for lactating cows.  While diets containing 21% forage-NDF are common, depending on forage availability, price and quality, diets can be found within a normal range of 16% 24% forage-NDF (DM basis).  Maximum NFC guidelines are positively related to forage-NDF content in diets for lactating cows.  Starch is the major component of the NFC fraction; ruminal and (or) total-tract digestibility of starch varies depending largely on grain type and processing.  Increased corn prices have created much interest in the potential for feeding reducedstarch diets.  Feed efficiency and IOFC results from the continuous lactation trials reviewed herein indicate that, for high producing cows in mid lactation, partially replacing corn grain with NDF from either high-fiber byproducts or corn silage to formulate reduced-starch diets was not beneficial.  Rumensin® increased milk production efficiency when added to both normaland reduced-starch diets.  Diets containing about 6% total sugar (DM basis) appear to be optimum.  Greater extent of high-moisture corn fermentation in the silo increases starch digestibility, apparently through degradation of the starch-protein matrix as reflected by increased ammonia concentrations.