Distribution of radiomanganese in the rumen of sheep

Twelve sheep, each prepared with a rumen fistula, were divided into three groups of four and fed three dietary levels of manganese (22, 300, and 3000 μg/g dry matter) for 11 weeks. The sheep were then dosed with radioactive manganese and samples of rumen contents were taken via the rumen fistula at 1, 7, and 13 h after dosing. The sheep were immediately killed after the last sampling and total rumen contents were mixed and sampled. Rumen fluid was separated from all samples and fractionated by centrifugation into protozoa plus plant particles, bacteria, and cell-free fraction. The bacterial cells were disrupted and fractionated into cell walls and cytoplasm. The cytoplasmic protein was precipitated with trichloroacetic acid.Although the concentration of radiomanganese in rumen fluid decreased with time after dosing from 14.4–17.8 to 6.1–9.3% of dose/L the protozoal and bacterial uptakes of radiomanganese were not significantly different and ranged from 26.5 to 40.6% and 18.9 to 31.7% of total in the rumen fluid, respectively. There was also no effect of dietary concentration of manganese on the uptake and distribution of radiomanganese in the rumen fluid fractions. However, on the average more radiomanganese was found in the bacterial cell walls (48.1–75.3% of total in bacteria) and less in the cytoplasm (51.9–24.7% of total in bacteria) with increasing dietary manganese. Very little radioactivity was found in the trichloroacetic acid precipitated cytoplasm (1.79–0.78% of total in cytoplasm). Concentrations of manganese in the bacteria and bacterial cell walls were higher than, and closely related with, those in the diet. Specific activities of radiomanganese decreased in all fractions with increasing dietary manganese. Approximately 15–17% of the total radiomanganese in the rumen contents at 13 h after dosing was found in the protozoal fraction and 10–15% was found in the bacterial fraction; only approximately 21% of the radiomanganese remained in cell-free fraction of the rumen fluid in each dietary treatment.