Relationships between in vitro gas production characteristics, chemical composition and in vivo quality measures in goats fed tree fodder supplements

Methods currently used to estimate the nutritive value of tropical forages fail to predict nutrient content and availability. The in vitro gas production technique has been proposed as a potential tool to evaluate tropical forages, Four tree fodder legume/maize stover (1:3, w/w) diets of known chemical composition, digestible OM intake (26.9-29.1 g DM-1 W-0.75 day(-1)), OM digestibility (520 to 540 g kg(-1) DM) and microbial nitrogen supply (0.43-2.68 g kg(-1) W-0.75 day(-1)) were used in in vitro gas production tests to evaluate the relationship between feed intake, digestibility and microbial nitrogen (MN) supply and the in vitro gas production characteristics and chemical composition. The tree fodder legumes used were Leucaena esculenta, L. diversifolia, L pallida and Calliandra calothyrsus. Two rumen fistulated goats fed on L leucocephala/maize stover diet (1:3, w/w) were used as donor animals for rumen liquor. Gas production from the fermentation of tree fodder legume/maize stover diets was measured in 24 and 96 h in vitro gas tests adapted to describe kinetics of fermentation based on the modified exponential model P = b(1 - e(-ct)). Correlation and simple and multiple regression analysis were used to test relationships between gas production parameters and chemical composition and in vivo data. Potential gas production (b), the rate constant (c) and gas volumes were negatively correlated to digestible organic matter intake (DOMI) and organic matter digestibility. There was, however a positive relationship between microbial nitrogen yield and intake (r(2)=0.60, p<0.001) and truly degraded NDF (r(2)=0.61, p<0.001). The rate constant, c, and gas volume at 24 h, V24, had a significant impact on DOMI (r(2)=0.42, p<0.01; r(2)=0.52, p<0.001, respectively). Gas volume at 96 h and truly degraded NDF were useful in predicting microbial nitrogen yield (r(2)=65, p<0.001). The effect of polyphenols on intake was low (r(2)=0.31, p<0.001) but not significant with OMD. The polyphenols accounted for 90% of the variation in gas production after 24 h, 80% for 96 h and 75% of the variation in the rate constant. (C) 1999 Elsevier Science B.V. All rights reserved.