Effect of Replacing Neutral Detergent Fiber of Forage with Soyhulls and Corn Gluten Feed for Dairy Heifers1,2

Abstract

Five duodenally and ruminally cannulated Holstein heifers were used in a 5 × 5 Latin square design to determine the potential of substituting NDF of soyhulls or corn gluten feed for forage NDF, and effects on site of nutrient digestion. All diets were formulated to contain 31% NDF, and diets had 85% (control), 65 or 45% (low or high corn gluten feed), and 65 or 45% (low or high soyhulls) of total NDF from corn silage and alfalfa hay (1: 1). Ruminal pH was lower at 3h postfeeding in heifers fed high versus low substitution diets. Ruminal disappearance in situ of NDF of alfalfa hay was higher when heifers were fed control diet and lower when they were fed high soyhulls, possibly mediated by ruminal pH. Total tract NDF digestibility was lower in heifers fed control than other diets, perhaps due to its higher proportion of less degradable forage NDF. Heifers fed low corn gluten feed or high soyhulls had reduced ruminal NDF digestibilities but greater total tract (and hindgut) NDF digestibilities than those fed high corn gluten feed or low soyhulls; heifers fed low corn gluten feed had faster ruminal fluid outflow, which may have increased passage of small, soluble particles. Low ruminal pH may have depressed ruminal digestibility of NDF by heifers fed high soyhulls. Duodenal N flow and efficiency of bacterial growth in the rumen were not affected by treatment. Apparent ruminal escape of soyhull protein was greater than for corn gluten feed protein. Results are interpreted to suggest that, in dairy rations containing by-products, 65% of dietary NDF as forage may be sufficient.