Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/1996
Publication Date: N/A
Interpretive Summary: Considerable knowledge exists regarding differences among forage sources in digestibility, and forage intake generally can be predicted from chemical composition with reasonable accuracy, although actual causes of such relationships remain unclear. Less information exists regarding differences among forage sources in efficiency of metabolism by the whole body and relatively metabolically active component tissues. Therefore, objectives of this experiment were to determine differences in net fluxes of oxygen and nutrients across the portal-drained viscera and liver with ad libitum consumption of tropical versus temperate grass, coarsely chopped or finely ground and pelletized. Results of this experiment indicate that efficiency of splanchnic tissue energy metabolism may differ between tropical and temperate grasses but will be comparably enhanced by fine grinding and pelletizing with similar increases in digestible energy intake. Factors responsible are unclear, but substantial effects on splanchnic tissue energy consumption apart from the quantity of absorbed energy are implicated. The absence of interaction between grass source and physical form suggests that physical characteristics influenced by fine grinding and pelletizing, presumably primarily that of decreased particle size without marked change in the proportion or integrity of arrangements of specific plant tissues, were not responsible for differences between grass sources in splanchnic tissue energy consumption relative to digestible energy intake.
Technical Abstract: Crossbred sheep (16, 8.5 mo of age and 33 +/- 0.9 kg) were used in a 21-d experiment (2 x 2 factorial) to determine effects on net flux of nutrients across the portal-drained viscera (PDV) and liver of ad lib. consumption of bermudagrass (B) vs ryegrass-wheat (RW) hay, coarsely chopped or finely ground and pelletized (G). Crude protein concentration was 86, 81, 113 and 119 g/kg and neutral detergent fibre concentration was 710, 688, 654 and 672 g/kg (dry matter basis) for B-C, B-G, RW-C and RW-G, respectively. Digestible energy intake (7.8, 12.0, 8.1 and 11.7 MJ/d for B, RW, C and B, respectively) differed (P<0.01) with grass source and form, and digestible nitrogen intake was 4.4, 7.0, 8.4 and 14.1 g/d (SE 0.82) for B-C, B-G, RW-C and RW-G diets, respectively. Consumption of oxygen by the PDV (142, 150, 131 and 160 mmol/h) and splanchnic bed (235, 257, 226 and 270 mmol/h for B, RW, C and G, respectively) was greater (P=0.07) for G than for C. The ratio of splanchnic energy consumption to digestible energy intake was greater (P=0.06) for B than for RW and numerically differed (P=0.14) between grass forms (0.374, 0.300, 0.278 and 0.219 for B, RW, C and G, respectively). Alpha-amino nitrogen release by the PDV (P<0.01; 25.8 vs 12.2 mmol/h) and uptake by the liver (P=0.07; 18.1 vs 10.7 mmol/h) were greater for RW than for B. Hepatic urea nitrogen release differed between grass sources (P=0.03) and physical forms (P=0.07; 17.7, 28.1, 27.0 and 18.8 mmol/h for B, RW, C and G, respectively). In conclusion, physical characteristics of forage influenced by G were not ones primarily responsible for differences between grass sources in splanchnic tissue energy consumption relative to digestible energy intake.