Effects of Sunflower Hulls on Digestibility and Performance by Growing Dairy Heifers Fed Varying Amounts of Protein and Fiber

A digestion trial involving 10 Holstein heifers evaluated rations containing 0, 10, 20, 30, and 40% sunflower hulls. Five experimental rations were isonitrogenous at 15% crude protein and 40% acid detergent fiber which was supplied primarily by alfalfa hay and sunflower hulls. Increasing the quantity of sunflower hulls in the ration decreased nutrient digestibility for dry matter, acid detergent fiber, and protein. Each 10% increment of sunflower hulls up to 40% of the experimental ration resulted in a reduction of digestibility coefficients for dry matter and acid detergent fiber, respectively, of 7.7% (linear regression coefficient; square correlation .90) and 4.9% (square correlation .78). Eight Holstein heifers were used for the feeding trial in two replicates of a 4 × 4 Latin square experiment to determine the nutritive value of sunflower hulls as a roughage source in growing ruminant rations. Treatment variables were two concentrations of crude protein, 12 or 18%, and two concentrations of acid detergent fiber, 19 or 30% of ration dry matter. Heifers fed rations containing 18% protein, 19% acid detergent fiber (27% sunflower hulls) achieved the highest gain (1.36 kg/day) and efficiency of growth (gain/feed, 20.5%). Animals on 27% sunflower hull rations consumed less feed and gained more than those on 50% sunflower hulls.