Effects of small ruminant type and level of intake on metabolism

Boer (BG) and Spanish goat (SG) and Rambouillet sheep (RS) wethers, ≥2.5 yr of age, consumed grass hay ad libitum (AL) or in restricted amounts (RI). Initial BW was 50, 74, and 40 kg for BG, RS, and SG, respectively. Intake of ME was 276, 230, and 281 kJ/kg BW0.75 for BG, SG, and RS (SE = 10.2) and 209 and 316 kJ/kg BW0.75 for RI and AL, respectively (SE = 7.7). Change in BW was lowest (P < 0.05) among animal types for RS (−0.18, −0.29, and −0.14 kg/day for BG, RS, and SG, respectively). Digestibility of NDF was similar among animal types. Total energy expenditure (EE) in kJ/kg BW0.75 was greatest (P < 0.05) among animal types for BG (363, 335, and 335 kJ/kg BW0.75 for BG, RS, and SG, respectively) and similar between levels of intake. Energy expenditure in MJ/day by the portal-drained viscera (PDV) (1.43, 1.25, and 1.17 MJ/day; SE = 0.118) and liver (1.16, 1.14, and 1.08 MJ/day; SE = 0.149) was similar among animal types. Both PDV (1.44 vs. 1.12 MJ/day) and liver EE (1.50 vs. 0.76 MJ/day) were greater (P < 0.05) for AL vs. RI. Net fluxes of ammonia N across the PDV (3.1, 2.4, and 3.0 g/day, SE = 0.50; 2.9 and 2.7 g/day, SE = 0.34) and liver (−4.1, −3.5, and −3.8 g/day for BG, RS, and SG, respectively (SE = 0.63); −4.3 and −3.2 g/day for AL and RI, respectively (SE = 0.48)) were similar among animal types and between levels of intake. Net flux across the PDV of UN was greatest among animal types (P < 0.05) for RS (−4.0, −1.4, and −3.6 g/day for BG, RS, and SG, respectively) and similar between intake levels (−3.5 and −2.5 g/day for AL and RI, respectively; SE = 0.47). Net flux of UN across the liver was similar among animal types (3.1, 3.3, and 5.2 g/day for BG, RS, and SG, respectively; SE = 1.34) and between intake levels (5.2 and 2.5 g/day for AL and RE, respectively; SE = 1.02). In conclusion, some findings indicate that with limited nutritional planes of this experiment, sheep were less able to reduce EE than goats, which may have involved differences in extra-splanchnic tissue metabolism. Likewise, N recycling appeared less extensive for sheep vs. goats, but to a magnitude less than to impact fiber digestion.