Influence of grass source on net flux of nutrients across splanchnic tissues in sheep with restricted intake

Crossbred wethers (22 months old; 46 +/- 1.3 kg body weight), with catheters in a hepatic vein, the portal vein and a mesenteric vein and artery, consumed warm (W; bermudagrass hay) or cool season grass hay (C; ryegrass-wheat) at 1.6% body weight (dry matter basis) in a crossover design experiment. Warm and cool season grasses were 13.6 and 9.9% crude protein, 77 and 66% neutral detergent fibre and 4.6 and 4.0% acid detergent lignin, respectively. Neutral detergent fibre digestibility (70.3 and 77.4%) and digestible energy intake (8.5 and 9.3 mJ/d) were greater (P < 0.02) for C than for W, and digestible nitrogen intake (11.5 and 8.0 g/d for W and C, respectively) was greater (P < 0.01) for W. Ruminal fluid concentrations of ammonia nitrogen and total volatile fatty acids were not altered by grass source, and acetate: propionate was greater (P < 0.02) for W (3.80) than for the C (3.54). Portal-drained viscera blood flow (118 and 119 l/h; SE 8.0), oxygen consumption (141 and 142 mM/h; SE 3.7), alpha-amino nitrogen release (13.4 and 13.1 mM/h; SE 3.42), urea nitrogen uptake (22.8 and 22.5 mM/h; SE 4.97), ammonia nitrogen release (14.9 and 15.7 mM/h; SE 3.36), glucose uptake (10.0 and 6.5 mM/h; SE 1.30), propionate release (14.5 and 16.4 mM/h; SE 1.88), lactate release (4.64 and 5.03 mM/h; SE 1.908) and acetate release (54.8 and 55.4 mM/h for W and C, respectively; SE 8.82) were similar between grasses. Energy consumption by the portal-drained viscera accounted for a slightly greater (P < 0.01) percentage of digestible energy intake with W vs C (18.8 vs 17.0%; SE 0.10). In conclusion, with restricted consumption of W or C by mature sheep, grass source had little impact on net flux of oxygen and nutrients across the portal-drained viscera and splanchnic bed.