Degree Name

BS in Animal Science


Animal Science Department


Marc R. Horney


Understanding the efficiency and digestibility of dietary nutrients in dairy heifers is essential for minimizing costs and environmental impacts of the dairy industry. The objective of this study was to interpret the effects of manipulating rumen-degradable protein (RDP) in a precision feeding system. Eight Holstein ruminally cannulated heifers (14.6 ± 0.1 mo of age, and 386 ± 9.1 kg of weight) were randomly assigned to 2 forage levels: HC (25% forage) and LC (75% forage) and to a degradable protein sequence [0% degradable protein from urea U, 100% casein C (no urea treatment U0); 33% U, 67% C (low urea treatment U2); 67% U, 33% C (high urea treatment U3); 100% U 0% C (all urea treatment U4)] within forage level administered according to a split-plot, 4 × 4 Latin square design with 21 d periods. Heifers fed HC had greater total apparent digestibility for dry matter (DM) digestibility and organic matter (OM) digestibility. Interactions were noted for neutral detergent factor and acid detergent factor(NDF & ADF) digestibilities with linear interactions for the LC forage level and quadratic interactions for the HC forage level. Similar results were noted for nitrogen (N) parameters including: digestibility, fecal N (g/d), urine N (g/d), total excreted N (g/d), retained N (g/d) and retained N (%). These results indicated linear interactions in LC forage diets with quadratic interactions in HC diets. The LCU0 treatment offered the highest utilization/retention of N within LC diets while the HCU2 diet offered the highest utilization/retention of N within HC diets. Overall, the HCU2 treatment offered the highest N efficiency among all treatments.