Comparative metabolism of zearalenone and transmission into bovine milk

The metabolism of zearalenone in the urine of the cow, the pig, the rabbit, the rat and man was studied. Both free and conjugated zearalenone (63%), α-zearalenol (32%) and β-zearalenol (5%) were present in the urine of the pig; α-zearalenol was the predominant metabolized species. In the cow, free and conjugated (glucuronic and sulphate) zearalenone (29%), α-zearalenol (20%) and β-zearalenol (51%) were found; in contrast to swine, β-zearalenol was the predominant species. In rat urine, the major species was free zearalenone, which constituted over 90% of the total zearalenone and metabolites. In the rabbit, 46% of the urinary metabolites took the form of zearalenone conjugates, 29% were conjugates of α-zearalenol and 25% were conjugates of β-zearalenol. The distribution of metabolites in the faeces was similar to that in the urine. In man, zearalenone and α-zearalenol were the major metabolites followed by β-zearalenol; all were in the glucuronide form.

Free and conjugated forms of zearalenone and diastereomeric zearalenols were present in cows' milk. The total concentration of zearalenone and its metabolites was 1·3 ppm (after receiving 25 ppm dietary zearalenone for 7 days); zearalenone constituted 35%, α-zearalenol, 31% and β-zearalenol, 34% of the free metabolites. α-Zearalenol is three times more oestrogenic than zearalenone.