Metabolic changes in the rumen following protozoal inoculation of fauna-free sheep fed a corn silage diet supplemented with casein or soybean meal.

Fauna-free wethers were fed bi-hourly a corn silage diet containing casein or soybean meal as a protein supplement. The wethers were inoculated via rumen cannula with a mixed population of ruminal ciliate protozoa. Ruminal fluid was sampled daily for 4 d before and for 13 d (and on d 28) after inoculation. Protozoal populations reached peak numbers on d 8 and decreased to new levels after d 9 for wethers on both supplements. Protozoa decreased (P less than 0.01) the concentrations of total volatile fatty acids, increased (P less than 0.01) the pH and decreased (P less than 0.01) he concentrations of total and non-ammonia nitrogen in ruminal fluid. The concentrations of ammonia nitrogen increased with increasing numbers of protozoa for wethers on both supplements, but the concentrations decreased after d 7 to approximately pre-inoculation levels for the casein-supplemented diet. The increasing numbers of protozoa were associated with the increased concentrations of total and free alpha-amino nitrogen (P less than 0.01) and sulfide (P less than 0.05) and with the decreased concentrations of soluble Cu (P less than 0.05) in the ruminal fluid in soybean meal-supplemented wethers but not in those receiving casein. It was concluded that dietary proteins with differing physical characteristics are metabolized to a different extent by ruminal ciliate protozoa, which in turn can affect the metabolism of other dietary nutrients such as nitrogen and sulfur and contribute to copper-sulfur interaction.