Studies of grazing of crop forages by sheep

Abstract

The composition and digestibility of ungrazed rape and of rape selected for similarity to that chosen by grazing wethers were determined. The composition of the rape consumed by these wethers was deduced from the content and digestibility of proximate constituents of the fæces. The digestibility of dry matter declined with delayed sowing and grazing. The digestive capacities of three wethers, for rape, were almost identical; a fourth was 2% lower. The digestibility of selected rape was only 0.4% higher than that of ungrazed rape and the difference was not significant. The composition of selected rape was intermediate between that of ungrazed and grazed rape. However, the latter was markedly lower in ether extract and crude protein and higher in crude fibre. Hand selection of rape similar to that chosen by the grazing wethers was thus only partly successful. The digestibility of leaf was little more than 2% higher than that of stem plus petiole, a smaller difference than was expected. Despite real differences in chemical composition, the nutritive value of grazed rape was only slightly lower than that of ungrazed rape. This illustrates the important effect of organic matter digestibility on food value. Although selective grazing clearly occurred, the effect on food value was negligible.