Influence of the β-adrenergic agonist cimaterol on energetic efficiency and oxygen consumption in liver tissue of growing lambs

Abstract

The effects of dietary cimaterol on energetic efficiency and liver oxygen consumption were evaluated using 14 wether lambs. Lambs were fed at a low intake (491 kJ kg−0.75 d−1 metabolizable energy (ME)) followed by a high intake (919 kJ ME kg−0,75 d−1). Five control animals received a pelleted alfalfa diet and five received a diet in which cimaterol was added at a level of 10.9 mg kg−1 dry matter. Four additional animals received no cimaterol at the low intake level and 10.9 mg kg−1 dry matter at the high intake. Indirect calorimetry measurements were conducted over a 24-h period on day 22 at each feeding level. Digestibility of dry matter and energy were not affected by cimaterol treatment. Methane production as a percentage of gross and digestible energy intake was increased (P = 0.04) 19% by cimaterol treatment at the 1.1 × M feeding level. Heat production was not affected by cimaterol treatment. Maintenance requirements (kJ ME kg−0.75 d−1) ranged from 314 to 438 for control and from 402 to 458 for cimaterol-treated lambs, depending upon the method of estimation. Energy costs of protein accretion (kJ ME kJ−1 deposited) in control lambs, estimated by a complete multiple regression procedure, by a multiple regression procedure following estimation of maintenance requirements by a semilog-linear procedure, and by assuming a constant efficiency for fat synthesis, were 4.85, 2.54 and 2.91, respectively. Corresponding values for cimaterol I lambs were 2.64, 1.65 and 1.98. Using estimates of protein synthesis obtained from radiolabelled leucine kinetics, the cost of protein synthesis was estimated as 1.25 kJ ME kJ−1 protein synthesized. Estimated energy costs of fat accretion were 0.56–1.13 and 0.94–1.30 kJ ME kJ−1 for control and cimaterol I lambs, respectively. Na+, K+-ATPase-dependent oxygen consumption rate of liver tissue tended (P = 0.06) to be reduced by 20% for cimaterol I compared with control lambs. Key words: Lambs, cimaterol, energy efficiency, protein, fat, Na+, K+-ATPase