Effects of isolation, confinement and competition for feed on the energy exchanges of growing lambs

Abstract

SUMMARY: 1. Calorimetric evaluation of the nutritive value of feeds for ruminants has, of necessity, involved using mature sheep isolated in respiration chambers. This experiment was designed to examine how such information relates to growing lambs reared in different ways.2. Lambs were either completely isolated, individually fed, or fed in groups. Two lambs in each group were fed to gain 100 g/day (medium) and two to gain 200 g/day (high). Calorimetric measurements were made on individuals or groups at intervals over 20 weeks.3. All lambs fed to gain 100 g/day consumed their entire ration, isolated lambs gained on average 123 g/day and the others 160 g/day. On the ‘high’ ration isolated lambs ate less than the others and gained 178 as against 228 g/day.4. Metabolizable energy intake, heat production and thus energy retention were similar in all groups offered the ‘medium’ ration. Differences in energy retention on the ‘high’ ration were related to differences in intake.5. The net availability for weight gain of the diet (k_f) estimated from energy balance trials conducted throughout the growth period (0·61) agreed well with that predicted from its content of metabolizable energy (0·63).6. Estimates of the caloric density of the weight gain suggested that on the ‘medium’ ration the isolated lambs retained substantially more energy as fat than those reared in groups. These observations are discussed in relation to the design and interpretation of calorimetric experiments to predict the nutritive value of feeds for growing lambs.