Abstract :
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.
