Ruminal degradation characteristics of some african rangeland grasses

Abstract

The seasonal rate and extent of dry matter (DM) and neutral detergent fibre (NDF) degradation of the African sourveld grasses Alloteropsis semialata, Andropogon appendiculatus, Cynodon dactylon, Elionurus muticus, Eragrostis plana, Harpochloa falx, Heteropogon contortus, Hyparrhenia hirta, Microchloa caffra, Themeda triandra and Tristachya leucothrix in the rumen were measured using the nylon bag technique at the Döhne Agricultural Development Institute, South Africa, in 1993. The size of the soluble fraction (SF) was markedly different (P < 0·05) between species, being largest in A. semialata (22·6%) and smallest in E. plana (13%). Over all species, the mean SF was highest (P < 0·01) in spring (21·6%) and lowest in winter (11·8%). Species differed (P < 0·05) in the size of the potentially digestible fraction (PDF), with H. contortus and T. leucothrix having the largest (71%) and M. caffra the smallest (53%) PDF. Mean PDF declined (P < 0·01) from spring (77·3%) through to winter (55·8 %). The rate of DM degradation (kd) in the rumen also differed (P < 0·01) between species, with C. dactylon and A. semialata having the fastest (0·054) and E. plana and A. appendiculatus the slowest (0·039) degradation rates. Mean kd values were lower (P < 0·05) in winter (0·039) than in the other seasons (0·048).

Neutral detergent soluble (NDS) content was highest in A. semialata (29%) and lowest in E. plana (21·5%). Species similarly varied in the amount of potentially digestible cell wall (PDCW), with E. plana having the highest (57%) and C. dactylon the lowest (45·1%) PDCW content. Mean PDCW content was highest in spring (59·5 %) and lowest in winter (44·6%). Cell wall degradation (kc) rates were fastest (0·04) in C. dactylon and slowest in M. caffra (0·03). Overall, kc declined from spring (0·039) through to winter (0·029). In general, A. semialata, T. triandra and H. hirta appeared to have the most favourable, and E. plana, A. appendiculatusand M. caffra the least favourable, ruminal degradation characteristics. These differences suggest that species composition is likely to have a major impact on potential animal production on these low quality grasslands.