The chemical composition and nutritive value of leaves of indigenous fodder trees

Abstract

The nutritional value of indigenous fodder plants has been reported to be high and constant throughout seasons as compared to grasses. The aim of this study was to evaluate the nutritional value of three tree species of the Combretum family, C. apiculatum, C. molle, C. zeyheri, and two other plant species, Colophospermum mopane and Pelthophorum africanum. This would be achieved through the determination of chemical composition (ash, dry matter (DM), organic matter (OM), CP, acid detergent fibre (ADF), acid detergent lignin (ADL), acid detergent indigestible nitrogen (ADIN), condensed tannins (CT) and ether extract (EE)), rumen degradability and in vitro digestibility of the leaves of these species were determined. The foliage of the tree species were collected in and north of Pretoria. After rinsing a portion of each species' samples, they were freeze-dried, prepared for analyses and stored as fresh samples pending analyses. The in situ analysis was done as blanket analysis over all the seasonal samples of each plant species excluding Mopane. This was done because the leaf materials collected were not enough to conduct a complete trial for each seasonal collection. Therefore sites were not considered for statistical analyses hence species were compared across seasons only. All the plant species exhibited a wider range of the chemical fractions. Their ash concentrations ranged from 30.3 g/kg DM for C. zeyheri to 85.8 g/kg DM forC. molle, NDF 270.3 g/kg DM for C. apiculatum to 410.1 g/kg DM for P africanum, ADF 208.1 g/kg DM P. africanum to 375.2 g/kg DM for C. molle. Their CP ranged from 62.9 g/kg DM for C. molle to 172 g/kg DM for Mopane, CT 65.6 mg sorghum tannin equivalent (STE)/g DM for C. zeyheri to 660.3 mg STE/g DM for Mopane, ADIN ranged from 1.2 g/kg DM for C. apiculatum to 3.3 g/kg DM in C. mopane. The range of some mineral concentrations of all the plants was not as wide as the other fractions. The concentrations of Ca ranged from 7.9 g/kg DM for Mopane to 16 g/kg DM for C. molle, K 1.2 g/kg DM Mopane to 7.8 g/kg DM for C. molle, Mg 1.4 g/kg DM for C. molle to 3.8 g/kg DM for C. apiculatum. The concentrations of Cu ranged from 7.8 mg/kg DM for C. molle to 66 mg/kg DM for C apiculatum, Fe 169 mg/kg DM for Mopane to 435 mg/kg DM for C. zeyheri. The in vitro dry matter digestibility (IVDOM) ranged from 52.6% for Mopane and C. zeyheri to 64.1% for C. apiculatum. The in situ degradability fractions for the Combretum species ranged as follows: soluble fraction was 4.02% for C. apiculatum to 25.4% for C. zeyheri; degradable fraction was 34% for C. zeyheri to 44% for C. apiculatum and the extent of nitrogen (N) degradation was 47% for C. apiculatum to 60% for C. zeyheri. The concentrations of the chemical fractions of all the plants did not show a particular seasonal trend. However significant and insignificant variations were observed. The CP concentrations were almost constant implying a better N supply to animals throughout the seasons. The CT concentrations were not high enough to adversely affect the digestibility of protein. The Combretum species showed reasonable N degradability in situ, C. zeyheri the most degradable. The plant's digestibility values were within the range of browse plants. These results cannot be conclusive on the eventual nutritional value of these plants to the animals. Further studies would be necessary to quantify the availability of the chemical fractions and the foliage's palatability to the animals.