Potential nutritive value of selected browse species from Kenya using in vitro gas production technique and polyethylene glycol

The aim of this study was to asses the nutritive value of twelve browse species commonly used for feeding livestock in Kenya using the chemical composition including polyphenolics, in vitro gas production and in vitro dry matter (DM) and organic matter (OM) degradability. The effect of tannins present in the browse forages was also assessed using polyethylene glycol (PEG-6000). The forages had high crude protein content (98.4-302.3 g/kg DM) and low to moderate neutral detergent fibre (190.2 - 570.4 g/kg DM). There was wide variation in tannin content ranging from low, moderate to high especially in Calliandra calothyrsus, Grewia bicolor and Terminalia brownii that had total extractable tannin content of more than 100 mg/g DM. Fractionation of condensed tannin flavonoids showed that the delphinidin/cyanidin ratio ranged from 0:100 to 87:13. All the species had high potential gas production except Terminalia brownii and Tamarindus indica that tended to show low gas production potential. The rate of gas production ranged from 2.1 to 15.0 %/h. Addition of PEG-6000 significantly increased gas production in all the species except in Balanites aegyptiaca, Boscia angustifolia, Maerua angolensis and Olea europaea. However, addition of PEG-6000 had mixed effects on DM and OM in vitro degradability. The effect was significant in Calliandra calothyrsus, Grewia bicolor, Terminalia brownii and Tamarindus indica (DM only). Addition of PEG-6000 significantly decreased the partitioning factor in all the species except Balanites aegyptiaca, Boscia angustifolia, Maerua angolensis and Olea europaea. Based on chemical composition, gas production and in vitro degradability, the browse species forages have high potential nutritive value especially as protein supplements to poor quality forages in the tropics. However, the presence of tannins in some of the browse species forages may adversely affect their potential nutritive value.