1 Powell, J. M.; Fern ndez-Rivera, S.; Williams, T. O.; Renard, C. (Eds.) 1994. Livestock and sustainable nutrient cycling in mixed farming systems of sub-Saharan Africa: Vol.II: Technical papers. Proceedings of an International Conference, International Livestock Centre for Africa (ILCA), Addis Ababa, Ethiopia, 22-26 November 1993. Addis Ababa, Ethiopia: ILCA. vii, 560p.