Roughage feeding of ruminants – new developments. This article is mainly limited to developments in improving the utilization of cereal straws by ruminants. Scanning electron microscopic studies have been applied in the study of the rate of roughage fermentation in the rumen and this technique could be applied in selection programmes to develop pasture cultivars with higher digestibilities. Various aspects of the adhesion of rumen bacteria to fibrous material have been studied with the aid of transmission electron microscopy. With regard to the chemical composition of roughages the most recent developments are the use of spectroscopic techniques such as ultraviolet, infrared absorbance and nuclear magnetic resonance. Specific reference is made to the various chemical reactions that take place during ammoniation of cereal straws. The present state of knowledge with regard to the formation of 4-methylimidazole (4-me-l) during ammoniation is summarized and the possible role of Mg in protecting animals against the toxic effect of 4-me-1 is discussed.