Factors affecting in sacco dietary degradation by Ankole cattle grazing natural range pastures in Uganda

Abstract

The in sacco disappearance of dietary dry matter after 48h of incubation in the rumen DM_d) was examined for its relationship with seasonal changes in neutral detergent fibre (NDF_d), crude protein (CP_d), cellulose (CELL), hemicellulose (HCELL), acid detergent lignin (ADL_d) and water solubility S_d); and with grazing time (G_t), live-weight (LW) and free water intake (W_i) of ten milking Ankole cows. Degradation was highly correlated (P = 0.05) with solubility (r = 0.83) and grazing time (r = –0.80), followed by dietary crude protein (r = 0.56), neutral detergent fibre (r = –0.55), cellulose (r = –0.55) and lignin (r = 0.52), but less so with hemicellulose (r = 0.45). Deficiency of soluble cell contents, particularly the crude protein fraction, was the most severe limitation to dietary degradation. Cattle tolerated high levels of cellulose in their diets throughout the year. It was concluded that protein supplementation could optimise dietary degradation and that cattle could benefit from longer grazing time to allow optimum dietary selection, degradation and feed intake.

Keywords: Ankole cattle, dietary selection, dry matter disappearance, free water intake, in sacco degradation, lignification, live weight change, predictive model, water solubility

African Journal of Range & Forage Science 2005, 22(3): 157–165