Veld condition and animal performance: Application of an optimal foraging model

Abstract

An optimal foraging model was used to predict food ingestion rate, food digestion rate and animal energy gains relative to requirements as functions of dietary composition. Energy gains were maximized by ranking food types in order of their effective value, as limited by either ingestion or digestion rate. This accommodated adaptive changes in food preferences. Input parameters represented veld in ‘good’, ‘medium’ or ‘poor’ condition. Output demonstrated a variable relationship between animal energy gain and veld condition score. Veld rated in ‘poor’ condition showed better gains than ‘good’ condition veld when food quality was limiting and when animal size was reduced. The model output suggests possible mechanisms leading to observed patterns, thereby focusing research needs. Optimal foraging models could be coupled with adaptive models of plant and soil responses to investigate longer term relations between grassland composition and animal production.