Energy efficiency in grazing lambs differing in sire body size, determined by the in vitro respiration rate and weight of liver and rumen

Abstract

The energy efficiency of four group of lambs sired by rams of different body size was inferred from observation of liver and rumen weights and in vitro respiration rates (both total and the part attributable to sodium, potassium ATPase activity). The animals were raised in a common grazing-dependent environment from birth (September 1996) until reaching a market weight of 42.5 ± 0.9 kg (December 1997). The four groups (four ewes and four wether lambs per group) were progeny of Corriedale and Romney Marsh dams with sires of the Hampshire Down (H), Texel (T), and Ile France (I) breed, or of the same breed as the dam, as the control (C). At slaughter, livers and rumens were weighed, and in samples (5-10 g) of the caudal lobule and ventral sac, respectively, oxygen consumption was measured polarographically. The Na+, K+-ATPase dependent respiration was measured as the difference in O2 intake before and after the addition of 1 mMof ouabain. The genotypes did not affect mean daily gain (86.2 ± 2.0 g). Neither were relative weights of liver and rumen (16.2 ± 0.2 and 21.3 ± 0.9 g/kg of body weight, respectively) nor in vitro O2 consumption in fresh liver tissue (63.0 ± 2.4 µmol h-1g-1) affected by sire breed. For fresh ruminal papillae tissue there were differences (P<.05), but of small magnitude, among groups in O2consumption (T, 8.0, C, 8.7; I, 9.5; and H, 10.3 µmol h-1g-1). In all breed groups Na+, K+-ATPase dependent respiration accounted for 30 to 34% of the total O2 intake in liver and rumen tissues. It is concluded that all four groups of lambs gained weight with essentially the same energy efficiency in this study under conditions of nonintensive nutrition.