Predicting animal production on sourveld: A sward‐based approach

Abstract

Simulation models were developed to assess the effects of sward structure and species composition on average daily gain (ADG) and seasonal live mass gain (LWG) in cattle and sheep on Döhne Sourveld. The models used diet quality and intake data collected from sites of different sward structures and species compositions on this veld type. In model 1, predicted ADG was highest at an optimum sward height (Hopt) of 60‐ 80 mm for sheep and approximately 120 mm for cattle but Hopt is likely to decrease as forage quality declines through the season. Species composition appeared to be the major determinant of ADG above Hopt while sward height appeared to be more important below Hopt. Potential rates of DM intake generally far exceeded predicted voluntary intake, suggesting that on sourveld, intake is seldom likely to be restricted by the effects of sward height on intake rate per se. In model 2, species composition had a major effect on animal production with sites showing large differences in predicted LWG. Significantly, site rankings in terms of predicted LWG were different between cattle and sheep and showed only limited agreement with veld condition score. In both models, small, apparently insignificant, differences in dietary quality translated into major differences in predicted ADG and LWG. Through their effects on diet quality, species composition and sward structure thus both appear to be important determinants of animal production on Döhne Sourveld. However, an optimum species composition and sward structure cannot be specified as these variables are conditional upon each other as well as the season and the animal species involved.