Vertical heterogeneity of chemical constituents and in vitro ruminal fermentation parameters in browse tree leaves

Abstract

Repeated herbivory has the potential to induce adaptive chemical changes in the leaves of browse plants, which can alter their nutritive value. This study examined the interactive effect of tree species and harvest height on chemical composition and in vitro ruminal fermentation in leaves of Grewia occidentalis, Rhus longispina, Ozoroa paniculosa and Scutia myrtina trees in a communal grazing area of Nkonkobe municipality, Eastern Cape, South Africa. Leaf samples were harvested within (0–1.5 m) and above (> 1.5 m) the browsing height for goats. The chemical composition, nitrogen solubility, in vitro ruminal dry matter digestibility and gas production parameters were influenced by browse species (p < 0.001). The leaves of R. longispina had the highest crude protein content (136  g/kg DM) and N solubility index (59.0%). Total soluble phenolics in G. occidentalis leaves was double that of R. longispina and around four times the concentrations in O. paniculosa and S. myrtina leaves. None of the tree species demonstrated an inductive biosynthetic chemical response to repeated herbivory. It was concluded that the leaves of R. longispina are potentially the best supplemental forage for poor-quality grasses because they had the highest CP and nitrogen solubility, and among most digestible leaves.