Field studies of grazing lambs without protozoa in the rumen indicated that live weight gains were 15% higher than in faunated lambs (Bird &nd Leng 1985). Poos et al. (1979) reported that monensin decreased protozoa1 populations in the rumen but Leng et al. (1984) found no effect of monensin on half life or growth rate of protozoa. However in previous studies (Habib, G. & Preston, T.R. 1984 unp...