In situ neutral detergent fibre digestibility, in vitro organic matter digestibility and methane production of four Namibian rangeland encroacher bush species used as fodder

Abstract

Encroacher bush species have been undervalued due to insufficient information about their potential feeding value. This study evaluated the in situ neutral detergent fibre (NDF) digestibility, in vitro organic matter digestibility (OMD) and methane production of Senegalia mellifera, Dichrostachys cinerea, Terminalia sericea and Rhigozum trichotomum. Leaves and twigs (≤ 20 mm) were harvested during late dry and early rainy seasons. The indigestible neutral detergent fibre (iNDF) and digestible neutral detergent fibre (dNDF) were determined by the in sacco nylon bag technique. The in vitro organic matter digestibility (OMD) of bush samples were based on the two-stage pepsin + cellulase solubility technique. Methane gas production was determined by in vitro method using the Gas Endeavour Automatic Gas Flow Measuring System. The iNDF for D. cinerea and S. mellifera decreased (P < 0.0001) from late dry to early rainy season, while that of R. trichotomum and T. sericea increased. Digestible NDF decreased (P < 0.001) from late dry to early rainy season for all species, except S. mellifera. Species and species x season interaction affected (P < 0.0001) OMD. Except for S. mellifera, the in vitro OMD decreased (P < 0.001) from late dry to early rainy season. In vitro methane gas production of all species was higher (P = 0.0004) during the late dry season compared to the early rainy season (147.6 versus 92.0 mL/g DM). In conclusion, based on the low OMD and high iNDF, the studied species may require further intervention to improve their digestibility and feeding value.