Predicting animal production on sourveld: A species‐based approach

Abstract

A simulation model was developed to predict average daily gain (ADG) in cattle and sheep grazing different species and swards of different species composition on Dohne Sourveld. The model was based upon measured ingestive and digestive characteristics of different grass species and incorporates an explicit digestive constraint based upon rumen mass and turnover rate. Sensitivity analysis indicated that forage quality, through its effects on digestion rate, had a far greater impact on predicted ADG than ingestion rate. There were major differences between grass species in their predicted potential to support ADG. Overall, predicted ADG was greatest for Hyparrhenia hirta, and to a lesser extent for Cynodon dactylon, but lowest for Andropogon appendiculatus, Eragrostis plana and Microchloa caffra. For all species, predicted ADG declined through the grazing season and most species appeared incapable of meeting animal maintenance energy requirements in winter. Predicted ADG increased with plant height in all species until the seasonal limit set by voluntary feed intake was reached. At all sites predicted ADG declined through the grazing period but the magnitude and rate of this decline was strongly dependent upon species composition in terms of the nutritive value and the relative and absolute abundance of the species present at a site. Species composition, through its effect on diet quality, is therefore likely to be a major determinant of animal production on Döhne Sourveld.