Effects of different supplements on splanchnic oxygen consumption and net fluxes of nutrients in sheep consuming bromegrass (Bromus inermis) hay ad libitum

Abstract

Fifteen sheep (53 kg), with catheters in a hepatic vein, the portal vein and a mesenteric vein and artery, were offered a bromegrass (Bromus inermis) hay (104 g crude protein (CP), 700 g neutral-detergent fibre and 65 g acid-detergent lignin/kg dry matter (DM) ad lib. with different supplements to determine the effects on net flux of oxygen and nutrients across the portal-drained viscera (PDV) and liver. The sheep were unsupplemented (Control) or received 5 g DM/kg body weight (BW) of ground maize (M), 7 g DM/kg BW of soya-bean hulls (H) or 0.73 g DM/kg BW of a mix of feedstuffs high in rumenundegradable protein (P). Apparent digestible energy (DE) intakes were 5.3, 10.4, 10.6 and 6.7 (SE 0.74) MJ/d and apparent digestible CP intakes were 37, 50, 79 and 68 (SE 4.3) g/d for Control, M, H and P treatments respectively. Splanchnic tissue oxygen consumption rates were 0.23, 0.32, 0.30 and 0.27 (SE 0.054) mol/h, and oxidative metabolism accounted for 0.46, 0.31, 0.33 and 0.47 (SE 0.051) of DE intakes for Control, M, H and P treatments respectively. Supplements increased (P < 0.05) release of alpha-amino nitrogen (AAN) by the PDV (4.2, 17.5, 19.6 and 18.1 mmol/h for Control, M, H and P treatments respectively). Splanchnic net flux of AAN was not affected by supplement treatments. Hepatic release of urea-N was increased (P < 0.05) by supplement treatments (27, 40, 46 and 44 mmol/h for Control, M, H and P respectively); the P treatment increased (P < 0.05) and the H treatment tended (P = 0.10) to increase splanchnic release of urea-N (7, 10, 20 and 27 mmol/h for Control, M, H and P treatments respectively). Net flux of glucose across the PDV was -4.6, 1.4, -5.6 and -7.2 (SE 1.65) mmol/h for Control, M, H and P treatments respectively. Hepatic glucose released averaged 23 (SE 2.0) mmol/h and was not affected by treatment. Treatments M and H increased (P < 0.05) PDV release of propionate compared with the Control treatment (4.5, 15.5, 16.8 and 7.7 mmol/h for Control, M, H and P treatments respectively). Release of acetate by the PDV was 43, 97, 118 and 67 (SE 23.9) mmol/h for Control, M, H and P treatments respectively. In summary, different supplements of low-quality grass did not increase the efficiency of N metabolism by splanchnic tissues. Treatment P had little effect on net flux across splanchnic tissues of glucose, L-lactate, beta-hydroxybutyrate and volatile fatty acids (VFA).(ABSTRACT TRUNCATED AT 400 WORDS)