The production of volatile fatty acids (VFA) was studied in vitro to assess the possible contribution of microbial fermentation to the energy economy of growing ostrich chicks. Structure, capacity and contents of the gastro-intestinal track were examined to identify major sites of microbial activity and VFA energy yield. Radioactive substrates were used to confirm that the products derived from fermentative digestion could provide nutrients to the host animals. In this experiment the theoretical energy contribution of VFA could be as high as 76% of the metabolizable energy intake of the growing ostrich chick. The absorption and oxidative metabolism of end products from cellulose fermentation was demonstrated to contribute to the metabolizable energy requirements of the growing ostrich.