Evaluation of feed value of leaves of tannin rich trees with or without tannin binding agents

Abstract

The study was undertaken to evaluate nutrient value of tannin rich tropical browse species and the interaction effects of these plant species and different level of tannin binding agents on in vitro fermentation parameters and to examine the relationship between some chemical composition parameters and the in vitro fermentation values of the plants. The studied plant species were Albizia gummifera, Carissa edulis, Draceana steudneri, Ficus sycomorus, Grewia ferruginea, Millettia ferruginea, Prunus africana, Rhus glutinosa, Syzygium guineense and Ekebergia capensis. The species were subjected to proximate, detergent, polyphenolic and in vitro analysis. Rumen liquor was collected from three Boran- Holestein Friesian cross bred bulls. Plant species was incubated for two run in three replications in each run. An in vitro gas production measurement was performed after 2, 4, 6, 8, 12, 24, 32, 48, 58, 72 and 96 h after incubation and their fermentation kinetics were described using the equation y = a + b(1-e-ct). Organic matter digestibility (OMD), metabolizable energy (ME) and short chain fatty acids (SCFA) were estimated for 24h gas production. The measurement of pH was performed before and after incubation in vitro. A wide variability in chemical composition including polyphenolics, in vitro digestibility and fermentation and estimated parameters recorded for plants as well as interaction of plant-tannin binding agents. The total phenols (TP) content (g/kg DM) ranged from 101 in D. steudneri to 288 in C. edulis, which also had the higher total tannins (TT) (204g/kg DM)(P<0.001). The highest soluble gas fraction (a) were recorded for C. edulis (20.73 ml) and R. glutinosa (20.71 ml), where as the lowest value was estimated for M. ferruginea (5.85ml (P<0.001)). Fermentation of insoluble fraction (b) was highest in G. ferruginea (190.77ml), P. africana (192.47ml) and S. guineense (188.17 ml) as compared to other species (P<0.001). C. edulis and R. glutinosa had the highest rate of gas production (c; 8.58, and 8.57 ml/h, respectively) as compared to rest of the species (P<0.001). Addition of PEG4000, PEG6000, PVP and PVPP to incubation medium increased the extent and rate of gas production all plant species as compared to species incubated without tannin binding agent (P<0.001). There were negative correlations between CT, NDF and ADF content of the plant species and the gas production at all incubation times. Negative correlation were also observed between CT and CP (r=-0.565), IVOMD (r=-0.722), IVDMD (r=-0.669), TDN (r=-0.668), DCP (r=-0.662) and DCHO (r=-0.427) (P<0.01). Addition of PEG, PVP and PVPP inactivate effects of tannins and increased gas production, SCFA, ME, and OMD in all the plants (P<0.001). Generally, treatments received PEG6000 and PEG4000 were found to be superior over other treatments in terms of rate and extent of gas production (p<0.001). Addition of PEG6000, PEG4000, PVP and PVPP could help to overcome adverse effects of tannins on nutrient availability as indicated by gas production parameters. This increase was noticeable in all plant species. Based on their nutrient content and fermentation kinetics as when its tannin content is biologically inactivated by using tannin binding agents the browse species may play an important feed supplements in providing sustainable fodder for herbivores.