Nutritive evaluation of some browse species

Abstract

Browse plants play an important role in providing fodder for ruminants in most parts of the World. However, the presence of tannins and other phenolic compounds in a large number of these feed resources limits their utilization as animal feed. This paper presents the nutritive value of some browse species based on their chemical composition (nitrogen, polyphenolics and neutral detergent fibre (NDF) content), dry matter (DM) degradability in sacco and gas production in vitro including the effect of the phenolic binding compound, polyethyleneglycol-4000 (PEG 4000), on in vitro gas production. The browse species evaluated were Calluna vulgaris (heather), Sarothamnus scoparius (broom), Ulex europaeus (gorse) and Chamaecytisus palmensis (tagasaste). The crude protein (CP) content was highest ( P < 0.05) in broom (189 g kg −1 DM) followed by tagasaste (175 g kg −1 DM) and gorse pre-flower (168 g kg −1 DM) and the lowest was in heather (98 g kg −1). Heather had the highest ( P < 0.05) concentration of the phenolic compounds compared with all the other species. Gorse in-flower contained a higher concentration ( P < 0.05) of total extractable phenols (TEPH), total extractable tannins (TETa) and NDF and a lower content of CP than gorse pre-flower which is a reflection of their stage of maturity. As a result, gorse pre-flower had a higher in sacco degradability and in vitro gas production than gorse in-flower. Heather had the lowest degradability values. The ranking order of the browse plants in gas production was gorse pre-flower > tagasaste > broom > gorse in-flower > heather which was similar to their in sacco degradability values. Increasing the amount of substrate incubated slightly depressed the amount of gas produced by the browse plants. The response to PEG treatment increased with increased concentration of phenolic compounds in the browse plants. Thus, in heather, gas production increased by 51% at 12 h of incubation as a result of PEG treatment while the response was zero in the species with a low content of phenolic compounds. The results show that the phenolic compounds depress in vitro gas production and that PEG treatment has a potential for improving gas production and fermentation of feedstuffs high in phenolics due to the binding of the phenolic compounds to the PEG.