The dry matter and nitrogen degradation of whole crop wheat cut at three stages of crop maturity

Abstract

The in sacco degradability technique (Paine, Crawshaw and Barber (1982)) is a useful method to evaluate the dry matter and nitrogen degradation characteristics of a forage in the rumen. Little information is available on the DM and N degradability of whole crop wheat. In a previous paper substantial variations in the nutritive composition of fermented and urea treated whole crop wheat forages were observed with increasing crop maturity. These variations were ascribed to changes in botanical composition of the forage with increasing maturity, for example the increasing contribution of grain in the dry matter elevated the starch content of the forage (Hill and Leaver (1991)). Givens, Moss and Adamson (1993) stated that whole crop cereals comprised of a cell wall rich straw fraction and a starch rich grain fraction. Therefore it could be suggested that variation in the relative proportions of these fractions would influence the fractional rate of degradation of the forage. Evidence to support this hypothesis was presented in Givens, Moss, Adamson and Reeve (1992) by incubating each fraction individually. The experiment reported was designed to compare the effect of stage of crop maturity, ensiling and urea treatment on the degradability of DM and N of whole crop wheat forages incubated as a total forage.An autumn sown crop of wheat (var. fortress) was cut at three stages of maturity being; growth stage 49 (boot), 71 (early milk) and 89 (hard dough) and three treatments were applied to the harvested forage. The treatments were fresh forage as harvested, ensiled and urea treatment with 40 kg/tonne DM. Six mature sheep (mean liveweight 76.9 kg), each fitted with a rumen cannula were used in the degradation trial.