INFLUENCE OF FEED PARTICLE SIZE ON RATE AND EFFICIENCY OF GAIN, CHARACTERISTICS OF RUMEN FLUID AND RUMEN EPITHELIUM, AND NUMBERS OF RUMEN PROTOZOA

Abstract

Sixty yearling steers were fed five all-concentrate diets differing in feed particle size (range 476–1525 μm geometric mean particle size), prepared by mixing different proportions of a ground and pelleted feed with steam-rolled grain. Average digestible energy content of the diets was 3.093 Mcal/kg. Steers fed the medium particle size feed ate more (P < 0.01) and gained faster (P < 0.05) than those fed the fine or coarse feed. Feed-to-gain ratios did not differ among groups. Rumen wall darkened in color as the feed particle size increased (P < 0.01). The incidence of rumenitis (P < 0.05) and of abnormal papillae (P < 0.01) in steers decreased as the feed particle size increased. However, numbers of protozoa in the rumen fluid increased as feed particle size increased (P < 0.01). At slaughter, the pH increased with increasing feed particle size (P < 0.05), but the viscosity and alkaline phosphatase content of the rumen fluids were similar among groups.