Effect of leaf size, thorn density and leaf accessibility on instantaneous intake rates of five woody species browsed by Matebele goats ( Capra hircus L) in a semi-arid savanna, Zimbabwe

Abstract

Browse instantaneous intake rate (IIR) is a product of bite size and bite rate which are constrained by plant morphology. We studied the effects of leaf size, thorn density and leaf accessibility on the IIRs of five browse species in semi-arid savanna over three leaf phenophases using cafeteria-style trials. Bite size was influenced by leaf size and bite rate by leaf accessibility, while thorn density had an impact on both bite size and bite rate. The lowest IIRs were recorded on the small leafed Acacia tortilis which also had the highest thorn density. Dichrostachys cinerea had the highest IIRs due to the large bite sizes. Although Terminalia prunioides and Commiphora pyracanthoides had small leaves, their arrangements in clusters allowed for higher IIRs, which were comparable to those of the large leafed D. cinerea. Instantaneous intake rate showed no clear trend in relation to leaf phenophase, although at early leaf the goats cropped smaller bites because of the small size of the newly sprouting leaves. We conclude that leaf size influenced IIRs through bite size, leaf accessibility through bite rate and thorn density through both bite size and bite rate.