AbstractsMedical & Health Science

The objective of this research was to determine the effects of increases in energy available for gain from increased small intestinal starch digestion (SISD) and dietary lipid source and amount on the efficiency of N use in cattle. Five ruminally, duodenally, and ileally cannulated steers were placed in a 5 × 5 Latin square. Each received duodenal infusion of 1.5 ± 0.08 kg/d raw cornstarch and either 0, 30.9 ± 0.59, 62.4 ± 1.16, or 120.4 ± 3.39 g/d Glu, or 387.9 ± 17.47 g/d casein. Casein increased (P = 0.05) SISD. Similarly, greater duodenal Glu linearly (P = 0.02) increased SISD. Starch flow to the ileum decreased (Linear = 0.04) in response to greater postruminal Glu. Ileal flow of ethanolsoluble starch was not affected by duodenal Glu (Linear = 0.16) or casein (P = 0.42). Fecal starch flow was decreased by Glu (Linear = 0.04) and casein (P = 0.01), thus increasing postruminal starch digestion in response to casein (P = 0.02) and Glu (Linear = 0.05). Urinary N excretion was not affected (P ≥ 0.30) by postruminal Glu flow but urine N was increased by casein (P < 0.01). Nitrogen balance was not affected by greater duodenal Glu (P ≥ 0.34) despite increases in SISD, but casein increased N retention (P < 0.01). Duodenal casein (P = 0.38) and increasing amounts of duodenal Glu (P ≥ 0.15) had no effect on N retained as a proportion of N intake. The same steers were fed cornbased diets with varying amounts and sources of lipid in a 5 × 5 Latin square. Diets contained no supplemental fat (CON), 4% supplemental saturated fat (tallow, 4S), 4% supplemental unsaturated fat (linseed oil, 4U), 8% supplemental saturated fat (tallow, 8S), or 8% supplemental unsaturated fat (linseed oil, 8U). Increasing level of lipid supplementation did not affect DMI; however, unsaturated lipid reduced (P = 0.05) DMI. Apparent ruminal OM digestibility tended (Linear = 0.08) to decrease with increasing dietary lipid. Total-tract digestibility of DM (Linear = 0.07), OM (Linear = 0.11), and NDF (Linear = 0.11) also tended to decrease in response to greater dietary lipid. Additionally, unsaturated lipid tended (P = 0.07) to reduce total-tract NDF digestibility compared to saturated lipid. Ruminal pH was not affected by treatment (P ≥ 0.35). Greater dietary lipid did not affect (P ≥ 0.30) total organic acid production; however, ruminal acetate (Linear = 0.05) and the ratio of acetate:propionate were decreased. Interestingly, ruminal acetate (P = 0.07), propionate (P = 0.06), and the ratio of acetate:propionate (P = 0.02) was affected by the interaction of source × level. Duodenal flow of microbial N was not different (P ≥ 0.17). Microbial efficiency was linearly (P = 0.05) increased with increased level of dietary lipid. Unsaturated lipid decreased urinary N (P = 0.02) and fecal N (P < 0.01). Despite altered urine and fecal N outputs, small variations in N intake, urinary N, and fecal N mitigated… Advisors/Committee Members: Derek W. Brake.