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.

‘n Optimale voermodel is gebruik om voedselinnametempo, voedselverteringstempo en dierenergietoename relatief tot vereistes, as funksies van voedingsamestelling, te voorspel. Maksimale energietoename is verkry deur voedseltipes te orden ten opsigte van die effektiewe waarde, soos beperk deur inname of verteringstempo. Aanpassingsveranderinge in voedselvoorkeure is so geakkommodeer. Invoer parameters is verteenwoordig deur veld in ‘goeie’, ‘medium’ of ‘swak’ toestand. Uitvoer is gedemonstreer deur ‘n veranderlike verhouding tussen dierenergietoename en veldkondisie stand. Veld benoem as ‘swak’ toestand het ‘n beter toename getoon as ‘goeie’ toestand veld wanneer voedingskwali‐teit beperkend was en wanneer dier grootte verminder is. Die model uitvoer stel moontlike meganismes voor wat lei tot waargenome patrone en sodoende, klem 16 op navorsingsbehoeftes. Optimale voermodelle kan gekoppel word aan aanpassingsmodelle van plant en grond reaksie om langer termyn verhoudings tussen veldsamestelling en dierproduk‐sie te ondersoek.

Additional index words:

• Diet choice
• grazing
• herbivores