The engulfment and digestion of bacteria by ciliate protozoa leads to elevated ruminal ammonia concentrations and reduced microbial protein flow from the rumen. Thus it has been suggested that the removal of protozoa from the rumen (defaunation) may be beneficial in animals fed low protein diets (Bird and Leng, 1978). However, existing laboratory methods for defaunation are unsuitable for practical usage. Here we investigated the effects of leaves from various African multipurpose trees (MPT) on the activities of rumen bacteria and protozoa in the hope of identifying naturally occurring defaunating agents.

Protozoa are responsible for over 90% of the bacterial protein turnover in the rumen (Wallace and McPherson, 1987), thus the breakdown of bacterial protein was used as an assay of protozoal activity. [14CJ-Leucine-labelled Selenomonas ruminantium was incubated in vitro with rumen fluid taken from four rumen-fistulated sheep receiving a diet of hay, molasses, fishmeal and a mineral and vitamin mixture (500, 299.5,100,91 and 9.5 g/kg respectively). Wheat straw (40 mg/ml) or a 70:30 mixture of straw and MPT was added 2 h before the addition of labelled bacteria. Samples were removed hourly for up to 4 h to follow bacterial degradation. Unlabelled leucine (2.5 mM) was added to the rumen fluid to prevent reincorporation of [14C]-leucine.