Effects of diet on the protozoa population in permeable continuous cultures of rumen contents.

1. Responses of the protozoa population to the composition and the components of the diet were studied in permeable continuous cultures of rumen contents. 2. In Expt 1 a study was made of responses to diets containing different combinations of rice straw, lucerne meal and mixed concentrates given to the cow supplying inocula for cultures. It was found that (1) when a diet devoid of concentrates was fed, entodiniomorphs decreased in numbers; (2) their numbers increased with the increase in the amount of concentrates; (3) holtrich numbers were hardly affected by the type of diet; (4) rice straw and lucerne meal were not essential for protozoa to survive in culture medium. 3. In Expt 2 responses were determined to diets containing different combinations of maize, maize starch, sugars (glucose-sucrose (1:1, w/w)), soya-bean meal and isolated soya-bean protein. The results suggested the following relationship between dietary component and protozoa population. (1) The diet rich in both starch and sugars sustains the increased numbers of protozoa on the whole. (2) The diet rich in starch and deficient in sugars decreases selectively Dasytricha and small species of Entodinium such as Entodinium minimum and E. nanellum. The other species of protozoa, especially large entodiniomorphs such as Ophyroscolex and Polyplastron, are maintained at relatively high levels. (3) The diet deficient in starch and abundant in sugars decreases general entodiniomorphs except small species, while the numbers of Holotrichs are kept at relatively high levels.