Inadequate nutrition is the main cause of low productivity by ruminants in sub-Saharan Africa. The primary feed resources in the region include natural pasture and crop residues that have tough texture, poor digestibility and are deficient in nutrients. These deficiencies can be corrected by supplementation with high-density feeds such as oilseed cakes and
proteins of animal origin. However,
protein sources such as oilseed cakes are beyond the economic reach of most farmers, while the incidence of
bovine spongiform encephalopathy in Western intensive animal production may be thought to argue against the use of animal
proteins. Local tree legumes have been investigated as potential supplements for ruminants because of their beneficial effect of increasing metabolizable energy intake, N intake and feed efficiency, and improving animal performance. However, our work has suggested that some plant materials may have a nutritional value beyond simply their nutrient content, i.e. as rumen-manipulating agents. The foliage of some tree legumes has been shown to be selectively toxic to rumen protozoa. Rumen protozoa ingest and digest bacteria and fungi, degrading their cellular
protein to NH3. Microbial
protein turnover due to protozoal predation in the rumen may result in the net microbial
protein outflow being less than half the total
protein synthesized. Results from in vivo experiments have clearly shown that duodenal flow of both undegraded dietary and
bacterial protein is generally increased by defaunation. However, no practical method has been developed to date to eliminate protozoa. Anti-protozoal plants may be promising, safe, natural defaunating agents.