Incorporation of rapeseed meal extracted by pressure in a diet for growing fattening bulls .2. Glucosinolates and their breakdown products in the rumen

Eight bulls from the Belgian Blue breed were offered diets in which soya bean meal and linseed meal were substituted by rapeseed meal (variety Samourai) in order to provide, respectively, 33, 66 and 100% of the protein. The glucosinolate content was equal to 17.6 mu mol/g dry matter. Analyses of wet residues from rapeseed meal incubated in the rumen showed a rapid decrease of the glucosinolate content which disappeared after 5 h of incubation. The 3-hydroxypent-4-enenitrile, the but-3-enylisothiocyanate and the 5-vinyl-1,3-oxazolidine-2-thione antinutritional factors obtained from the glucosinolates were identified by GC-MS during the first 5 h. The 3-phenylpropanenitrile, the 3-methylindol, the 2-phenylacetic and 3-phenylpropanoic acids were also present in the residues and in the rumen. Although high sensitivity of the methods were used, no glucosinolates and their direct breakdown products were detected in the liquid and the solid content of the rumen.