Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/1996
Publication Date: N/A
Interpretive Summary: Forages differ in their rate and pattern of digestion with time in ruminants. However, it is unknown if such differences influence energy and nutrient use by internal organs such as the gut and liver. This is very important because the gut and liver together account for approximately one-half of the heat produced by ruminants. If a complete understanding of factors affecting energy use and wasteful heat production by the gut and liver is achieved, then diets can be better formulated and forages better managed to maximize energy and nutrient uptake by lean tissues of greatest value to humans. In this study, high heat production by the gut plus liver early after feeding a legume, compared with temperate and tropical grasses, did not affect heat production later after meals. Hence, differences among forages in efficiency of energy metabolism in the whole body and, thus, efficiency of feed utilization, do not appear caused by differences among forages in the pattern of change with time post-feeding in nutrient digestion and absorption. These results are quite important in that they indicate that differences among forage diets in level and efficiency of production by ruminants are determined by the interrelated factors of feed intake, digestion and efficiency of metabolism; however, apparently efficiencies of metabolism by the gut and liver are not affected by the pattern of forage digestion and subsequent nutrient and energy absorption. Therefore, future research should be directed towards study of the former three factors and should be not focused on the temporal pattern of forage digestion.
Technical Abstract: Crossbred wethers were used to determine the temporal pattern of net fluxes of oxygen and nitrogenous compounds across the portal-drained viscera (PDV) and liver in wethers consuming alfalfa (A), ryegrass-wheat (RW) or bermudagrass (B) hay three times daily (8-h feeding intervals). Alfalfa, RW and B were 57, 70 and 77% neutral detergent fiber and 15, 9 and 6% crude protein, respectively. Feed intake was ad libitum in Experiment 1 (A, RW and B; 37 +/- 1.8 kg BW and 11 mo of age) and set at 2.0% of BW (DM) in Experiment 2 (A and B; 34 +/- 2.0 kg BW and 12 mo of age). In Experiment 1, digestible energy intake was 2.96, 3.29 and 2.40 Mcal/d (SE 0.316), and digestible N intake was 17.7, 10.2 and 5.5 g/d (SE 0.99) for A, RW and B, respectively. Splanchnic oxygen consumption over an 8-h period was affected (P=0.05) by a treatment by time post-feeding interaction (A: 451, 310, 233, 309, 247, 261, 237 and 238 mmol/h; RW: 222, 164, 257, 200, 243, 274 and 329 mmol/h; B: 265, 184, 303, 323, 323, 334, 325 and 317 mmol/h at 1, 2, 3, 4, 5, 6, 7 and 8 h post-feeding, respectively (SE 45.4)) because of a similar interaction (P=0.08) in hepatic oxygen consumption. In Experiment 2, PDV oxygen consumption did not differ (P>0.10) with time post-feeding. In conclusion, A consumed ad libitum resulted in a different temporal pattern of splanchnic bed oxygen consumption than RW or B, but it did not appear that high oxygen consumption early after feeding A impacted subsequent consumption.