Crossbred wethers (18 months old; 44 ± 0.7 kg body weight), with catheters in a hepatic vein, the portal vein and a mesenteric vein and artery, consumed ad libitum tropical or temperate grass hay each of three different qualities or stages of maturity. Splanchnic tissue energy consumption was similar among tropical grass diets but increased as quality of temperate grass declined. Portal-drained viscera oxygen consumption increased with increasing digestible energy intake and fecal neutral detergent fiber excretion. Energy available to extra-splanchnic tissues with highest quality grass was greater for temperate than for tropical grass because of lower splanchnic tissue energy consumption relative to digestible energy intake. Grass source, quality and nitrogen concentration did not significantly affect portal-drained viscera release of α-amino nitrogen. Hepatic uptake of α-amino nitrogen was greater for tropical than for temperate grass, presumably because of higher nitrogen concentration with greater hepatic ammonia nitrogen uptake. Glucose uptake by the portal-drained viscera was greater for tropical than for temperate grass, and the potential contribution of propionate to hepatic glucose release tended to be greatest for grass highest in quality. Grass quality appears more important to achieve maximal energy availability to extra-splanchnic tissues with temperate than tropical grass.
- Forage quality