Some effects of diet on the mitotic index and the cell cycle of the ruminal epithelium of sheep.

The mitotic index of the ruminal epithelium increased rapidly when the diet of sheep was changed from one based on roughage to a concentrate-based diet. After several days the mitotic index declined to a new level which was slightly higher than that observed initially. Autoradiography of sections of rumen epithelium was used to construct percent labelled mitoses curves, from which the duration of the phases of the cell cycle was determined. The duration of the cell cycle was about 24 hr but decreased to 17 hr when cell proliferation was stimulated by changing the diet of the sheep from roughage to concentrate. The decrease in cell cycle time was mainly the result of the decreased duration of the phase of DNA synthesis (S phase). Data obtained from measurement of the cell cycle, together with the labelling index, were used to calculate the turnover times of the basal cell layer, and to estimate 'turnover' times for the entire epithelium. The mean turnover time for the epithelium was 16.5 days when sheep were fed a roughage-based diet, 10.9 days when fed a concentrate basal diet and 4.3 days when the sheep were in transition between the roughage and the concentrate diets.