Red clover silage is an important component of many organic dairy systems. The high intake and milk production potential of red clover silage has been recognised for many years (e.g. Thomas et al., 1985). Our earlier studies confirmed this potential and showed additional benefits with increased polyunsaturated fatty acid (PUFA) content of milk (Dewhurst et al., 2002). The objective of this study was to investigate further the effect of red clover silage on milk PUFA and to examine whether supplementary vitamin E, which is needed to slow oxidative deterioration of milk with enhanced PUFA content, had an effect.