Abstract
The purposes of this experiment are to measure the chemical composition of actually grazed herbage and to determine the relationship of herbage intake to the chemical composition of herbage when Holstein steers are grazed on orchard grass dominant pasture. DM intake of grazing steers was determined by a herbage-cutting technique. The chemical composition of the grazed herbage was estimated from the difference between the chemical composition of the whole herbage in protect cage and that of the residual herbage after grazing. The grazed herbage was higher in crude protein (p<0.01) and ether extract (p<0.05) and lower in NFE (p<0.01) than the whole herbage. There were significantly positive correlations between all components of the grazed and the whole herbage (p<0.01). These results indicated that chemical composition of the herbage, actually consumed by steers, was different from the composition of the sward, but the composition of the grazed herbage was influenced substantially by the composition of the sward. DM intake of grazing steers was negatively correlated to crude protein (r=-0.690), ether extract (r=-0.690), crude ash (r=-0.517) and CP/NFE ratio (r=-0.746) of the grazed herbage, and was positively correlated to NFE (r=+0.629) of the grazed herbage. Furthermore, the rumen NH_3 concentration of steers was negatively correlated to DM intake (r=-0.581) and to NFE of the grazed herbage (r=-0.674) and positively correlated to crude protein (r=+0.659) and CP/NFE ratio (r=+0.706) of the grazed herbage. These results indicated that herbake intake of grazing steer on orchard grass dominant pasture was influenced by the chemical composition of the herbage, especially crude protein and NFE contents, and that the rumen NH_3 concentration was also influenced by these two components of the herbage and might affect the herbage intake of grazing steers.
