Degradation characteristics of some Sudanese forages and tree pods using in sacco and gas production techniques

Fourteen Sudanese plant species were studied for their degradation characteristics, using nylon bag and gas production techniques. With the latter technique, all plant species were either treated with polyethylene glycol (PEG) to remove the phenolic anti-nutritional factors or left untreated. The plant species included four grasses, five legumes and four tree pod species. Grass and legume forages were collected during the rainy season, while the tree pods were collected during the dry season from a rangeland in western Sudan. The grass species included Blepharis linariifiolca, Dactyloetenium aegyptium, Echinochloa colona and Eragrostis tremula. The legume species included Trebulus terrestris, Solanum doblium, Inigofera spp., Sesamum alatum, Stylosanthes frauticosa and Zornia glochidiata. The tree pods included Buahania rufescens, Dichrostachys glomerata, Fehderbia albida and Phostigma reticulata. The degradation characteristics of the plant species were measured by incubating the samples in nylon bags for 8, 16, 24, 48, 72, or 96 h in the rumen of three sheep fitted with rumen cannula and given hay plus grass cubes. For the in vitro gas technique, the samples were incubated for 4, 8, 12, 24, 48, 72 and 96 h, using rumen inoculum of two of the sheep used for the nylon bag. The result of dry matter (DM) disappearance from nylon bag and gas volume recordings were fitted into the exponential equation of the form P = a + b(1 - e(-ct)), where P is the DM loss at time t and a, b and c are constants [J. Agric. Sci. Camb. 96 (1981) 251]. The degradation rate (c) of DM showed a large variation between the different plant species it was the highest with legumes followed by tree pods and grasses. The potential degradability (a + b) ranged from 68.9 to 76.9 for tree pods but it was nearly the same for grasses and legumes (54.6-72.4 and 54.7-75.2, respectively). For all plant species the major part of DM loss occurred between 24 and 48 It. The negative values of the rapidly fermentable fraction, a, pointed to the general occurrence of a lag phase, that is, the intercept (a) was negative. The potential gas volume (a + b) was higher for the samples treated with PEG, reflecting the presence of anti-nutritional factors. These were higher for legumes than tree pods or grasses. Using the degradation characteristics a, b and c in a multiple regression analysis, the correlation coefficients with in sacco and in vitro degradation characteristics of plant species, showed the highest correlations at 8 h (r(2) = 0.61, P < 0.001), 12 h (r(2) = 0.63, P < 0.001) and 24 h (r(2) = 0.06, P < 0.005). (C) 2003 Published by Elsevier B.V.