Energy metabolism in lambs fed silage diets with sucrose or a growth promoter

Abstract

The effect of feeding silage with sucrose or Avotan added was examined. A first cut, ryegrass silage was fed at maintenance and 1.5 times maintenance either alone, with sucrose added to make the total water soluble carbohydrate content of the diet up to 150 g kg −1 DM or with Avotan added at 45 mg kg −1 mean DM intake to wether lambs of initial mean weight 42.2 kg. Digestibility, nitrogen (N) and energy balance and efficiency of utilization of metabolizable energy (ME) for growth ( kf) were determined by open circuit calorimetry. Digestibilities of N and energy were, respectively, 0.720 and 0.754 for silage plus sucrose, 0.734 and 0.732 for silage plus Avotan and 0.743 and 0.742 for silage fed alone. Faecal N losses were significantly higher ( P < 0.001) for the sucrose diet, but there were no significant differences in urine N or in N retention among the diets. Significantly lower ( P < 0.01) faecal, urinary and methane energy losses and significantly higher metabolic heat losses for the sucrose diet were found when compared to silage alone. Avotan had no significant effect on energy metabolism. Efficiencies of utilization of ME for growth ( kf) were 0.54 for silage plus sucrose, 0.30 for silage plus Avotan and 0.43 for silage alone. Adding Avotan did not affect methane production or kf significantly, but the addition of sucrose reduced methane energy losses significantly ( P < 0.01) and increased the efficiency of utilization of dietary ME.