The quantification of grazing capacity from grazing — and production values for forage species in semi-arid grasslands of southern Africa

Abstract

The relation between rangeland condition and grazing capacity was determined along a degradation gradient. In studying agronomic values of forage species, the average production per tuft was combined with its grazing preferences, to link grazing values for species in the semi-arid grasslands of southern Africa. A production index, based on mean mass per tuft, was first compiled for species. Preference utilisation ratio of species was estimated for each of cattle and sheep, from the proportion of each species found in the diet relative to the proportion of the species found in the forage on offer. A microhistological technique was applied to oesophageal fistula samples to determine the proportion of each species found in the diet. Grazing values and grazing index were determined from the production and preference utilisation ratio of species. Where grazing values of species were determined subjectively in the past, in this study species were objectively classified based on estimated grazing values. Meaningful relationships between rangeland condition and grazing capacity were determined, along a degradation gradient, with the long-term coefficient of forecasting more than 75%. The financial implication with respect to sustainable animal production and rangeland condition variation was also calculated.