Effect of the liveweight of caged sheep on the digestibility of grasses fed ad libitum

Abstract

To determine the effect of liveweight on the digestibility of dry matter, 29 grass cuts were each fed ad libitum to between five and ten sheep of the same age. In the complete experiment 255 different sheep were used. All 255 observations were used to calculate regressions relating digestibility to liveweight for each of the 29 grasses. When the data were divided into four digestibility groups (< 50, 50-55, 55-60, > 60%) the regression coefficient for grasses with a digestibility less than 50% was 0.373 (P < 0.01). The regression coefficient for the other three groups varied between -0.080 and 0.049 (P> 0.05). The data were also analysed by comparing the results obtained with the heaviest and lightest sheep on each of the 29 cuts. When the 29 cuts were divided into four groups, as described above, there was no significant difference in mean digestibility between heaviest and lightest groups for feeds having a digestibility greater than 50%. For cuts with less than 50% digestibility the heaviest sheep digested the grass 4.2 percentage units more efficiently than the lightest sheep (P < 0.05). There were no significant differences in the level of feed residues. It was concluded from both methods of analysis that any effect of liveweight on the digestive efficiency of sheep is limited to forages with a dry matter digestibility less than 50%.