In vivo digestibility and effect of supplemental mucuna forage on treated rice straw degradation

Abstract

The objective of this study was to determine the digestibility of mucuna ( Mucuna pruriens var utilis) forage and changes in the rumen degradation kinetics of a basal diet of sodium hydroxide (NaOH)-treated rice straw supplemented with mucuna forage. In vivo digestibility of the forage was determined by difference, using four rams (mean weight of 21.4±1.22 kg) each fed either treated straw alone or supplemented with mucuna forage over two periods. In determining degradation kinetics, three rumen fistulated sheep (mean weight of 25.4±1.81 kg) were fed treated rice straw only, or supplemented with 10, 20 or 25% mucuna forage. Dacron bags containing treated straw were incubated in the rumen for 3, 6, 12, 24, 48, 72 and 96 h. Dry matter (DM) and neutral detergent fibre (NDF) disappearance and degradation kinetics were determined. In vivo digestibility of DM and organic matter (OM) of treated straw (59.0 and 60.8%, respectively) were not significantly different from those of treated straw plus mucuna forage (61.5 and 63.3%, respectively). However, both were lower ( P<0.05) than the estimates for the forage only (70.8 and 71.8%, respectively). Crude protein digestibility (CPD) of treated straw plus mucuna diet (55.2%) was higher ( P<0.05) than for treated straw only (44.3%), and both significantly lower than that estimated for the forage (68.3%). Supplementation with 20 and 25% mucuna forage improved the rate of degradation of both DM (0.040 and 0.022, respectively) and NDF (0.038 and 0.023, respectively) of straw compared with the control of treated straw only (0.014 and 0.015%, respectively). Supplementation level of 20% elicited the highest degradation rate of both DM and NDF (0.040 and 0.038%, respectively). It was concluded that mucuna forage supplementation contributed towards improving NaOH-treated rice straw degradation in the rumen and thereby could help improve the utilisation of treated rice straw and similar low to medium quality roughages by ruminants in the tropics.