Although the nutritive value of forage brassicas for lambs has been found to be high, as described by digestibility values of approximately 0.8 or higher, performance of lambs finished on these crops has been low and unpredictable. One of the possible reasons for such low and variable performance is low voluntary food intake which has been attributed to the presence of anti-nutritive factors such as SMCO and glucosinolates in the vegetative material. Glucosinolates undergo enzymic hydrolysis following chewing and the addition of saliva to produce a number of toxic metabolites including isothiocyanates, vinyloxazolidine-thiones and nitriles. (Fenwick et al, 1983). Historically, isothiocyanates were considered to be the major glucosinolate hydrolysis products (Kjaer, 1960); however more recent studies have shown nitriles to predominate under natural conditions such as those occuring during plant autolysis (Cole, 1976). The aim of the present study was to determine whether glucosinolates, following their hydrolysis to nitrile compounds in vivo might be responsible for low intake among lambs offered forage brassicas.