RELATIONSHIPS BETWEEN CHEMICAL-COMPONENTS OF VELD HERBAGE AND IN-VITRO DIGESTIBILITY AND ESTIMATED INTAKES OF DRY-MATTER AND DIGESTIBLE DRY-MATTER BY SHEEP AND CATTLE

The relationships between certain chemical components of fertilized and unfertilized Cymbopogon-Themeda summer veld herbage, and its in vitro digestibility and pasture intake by Merino sheep and Simmentaler cattle, were determined in the summer rain area in the Republic of South Africa. The herbage was represented by a wide range of grass species with, according to the literature, different palatabilities. The palatable species were more abundant (P < 0.001) on the fertilized veld than on the unfertilized veld. Sheep selected herbage with higher (P < 0.01) contents of crude protein (CP) and lower acid detergent fibre (ADF) and neutral detergent fibre (NDF) than that selected by cattle. The in vitro dry matter digestibility (IVDMD) of herbage selected by sheep was also (not significantly) higher. Highly significant (P < 0.01) correlations were found between the IVDMD of the pasture and CP content (r=0.817), ADF content (r=-0.858) and CP+ADF content (multiple regression) (r=0.881). The relationship between IVDMD and NDF content, was not significant. Data from unfertilized areas and fertilized areas could be described by a single regression equation for each chemical characteristic. With sheep, dry matter intake (DMI) and digestible dry matter intake (DDMI), respectively, showed highly significant correlations (P < 0.01) with CP content (r=0.639 and r=0.714), sulphur (S) content (r=0.796 and r=0.844), ADF content (r=-0.924 and r=-0.922) and NDF content (r=-0.705 and r=-0.729). In the case of cattle, DMI and DDMI, respectively, had highly significant relationships (P < 0.01) with CP content (r=0.720 and r=0.788), ADF content (r=-0.806 and r=-0.892) and CP+ ADF content (r=0.789 and r=0.900). Data from the unfertilized veld and fertilized veld could be described by a single regression equation for each chemical characteristic. Under the conditions described, some of these relationships can be used fairly reliably for relatively rapid and low cost prediction of potential nutritive value of the summer veld herbage.