The digestibility and voluntary intake of the leaves of trees and shrubs by sheep and goats

Abstract

The dried leaves of four species of shrub (Atriplex vesicaria, A. nummularia, Maireana pyramidata and Bassia diacantha) and four species of tree (Acacia pendula, Casuarina cristata, Geijera parvifora and Heterodendrum oleifolium) that are common to western New South Wales were fed to either sheep or goats to determine their digestibility. Four species were of low digestibility (< 50%) and one (C. cristata) had a digestibility of only 29%. Those of higher digestibility (A. nummularia 69%, M. pyramidata 58%, G. parviflora 59%) were only eaten sparingly: Digestibility alone gave a poor assessment of forage value because there was no correspondence between digestibility and organic matter intake. The intake of C. cristata (lowest digestibility) was much greater than that of A. nummularia or G. parviflora (highest digestibilities). There was good agreement (within 1 or 2 digestibility units) between in oitro (two-stage pepsin) and in vivo digestibility for six forages, but a greater disparity for M. pyramidata and H. oleifolium.

For the trees the digestibility of cell wall constituents and acid-detergent fibre was low, in some cases less than 10%. This was not related to the amount of acid-detergent lignin in the fibre. Most samples were high in nitrogen (above 2%), which had a true digestibility ranging from 66 to 98%.