Effects of Defaunation on Feed Digestibility,

T HE role of rumen protozoa in ruminant metabolism has received increasing attention during the past few years. Increased rates of gain by lambs containing protozoa compared to protozoa-free lambs were reported by Abou Akkada and el-Shazly (1964) and Yoder et al. (1964), who demonstrated that certain rations are more readily digested by faunated than by defaunated lambs. Greater rumen ammonia concentrations and altered rumen volatile fatty acid proportions were reported by Christiansen et al. (1965), when faunated animals were compared with protozoa-free animals. These results have been confirmed by Abou Akkada and el-Shazly (1965), who also found increased nitrogen retention in faunated lambs when compared with defaunated animals. Greater concentrations of protozoa resulting from feeding antibiotic to lambs (Klopfenstein et al., 1964; Purser et al., 1965) suggest that protozoa may be involved in the favorable response to antibiotic exhibited by growing animals. Further Mochrie (1964) suggested that protozoa are responsible at least in part for the favorable response to frequent feeding of ruminants. The present study investigated further the influence of protozoa upon ruminant metabolism.