There is increasing interest in the use of red clover (Trifolium pratense) as a high protein forage crop to finish growing lambs. Red clover contains the isoflavanoid compound formononetin which is converted to the non-steroidal oestrogen analogue equol by rumen micro-organisms. Equol is absorbed by the animal, and can have significant effects, such as suppressing reproductive cycling in ewes. Very few commercial red clover varieties have been bred with a low formononetin content to prevent this problem. Although human health benefits have been linked to the consumption of oestrogenically active compounds in foods such as soya (Kurzer and Xu, 1997), there is a need to investigate the presence of oestrogenically active compounds in animal products. The objective of this study was to investigate plasma metabolite and hormone concentrations, and the residual levels of equol in meat, of lambs grazing two varieties of red clover differing in their formononetin contents, compared to control animals grazing grass.