NUTRITIVE EVALUATION OF SOME BROWSE SPECIES

Browse plants play an important role in providing fodder for ruminants in most parts of the World. However, the presence of tannins and othe r phenolic compounds in a large number of these feed resources limits their utilization as animal feed. This paper presents the nutritive Va lue of some browse species based on their chemical composition (nitrog en, polyphenolics and neutral detergent fibre (NDF) content), dry matt er (DM) degradability in sacco and gas production in vitro including t he effect of the phenolic binding compound, polyethyleneglycol-4000 (P EG 4000), on in vitro gas production. The browse species evaluated wer e Calluna vulgaris (heather), Sarothamnus scoparius (broom), Ulex euro paenus (gorse) and Chamaecytisus palmensis (tagasaste). The crude prot ein (CP) content was highest (P < 0.05) in broom (189 g kg(-1) DM) fol lowed 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 hig hest (P < 0.05) concentration of the phenolic compounds compared with all the other species. Gorse in-flower contained a higher concentratio n (P < 0.05) of total extractable phenols (TEPH), total extractable ta nnins (TETa) and NDF and a lower content of CP than gorse pre-flower w hich is a reflection of their stage of maturity. As a result, gorse pr e-flower had a higher in sacco degradability and in vitro gas producti on 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 simi lar to their in sacco degradability values. Increasing the amount of s ubstrate incubated slightly depressed the amount of gas produced by th e browse plants. The response to PEG treatment increased with increase d concentration of phenolic compounds in the browse plants. Thus, in h eather, gas production increased by 51% at 12 h of incubation as a res ult 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 feedstuff s high in phenolics due to the binding of the phenolic compounds to th e PEG. (C) 1997 Elsevier Science B.V.