Residues of cyromazine and its metabolite melamine in eggs of laying hens following consumption of cyromazine contaminated feed

Eggs were recently found to be contaminated with melamine in China. This study was aimed to determine if the cyromazine contaminated feed could metabolite to melamine in eggs. First, a HPLC method was developed to determine cyromazine and melamine residues simultaneously in eggs. The limit of detection and the limit of quantitation were all 0.2 mu g/g. Second, a total of 72 laying hens were divided into four groups and were fed diets spiked with 0, 5, 15 or 50 mg of cyromazine per kg of feed for nineteen days, and then non- contaminated feed for next seven days. Eggs collected on days 0, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 23, 24 and 26 were analyzed for cyromazine and its metabolite melamine in whole eggs and eggs collected on odd days were analyzed in egg whites and egg yolks. This study illustrated that if only treating with cyromazine contaminated feed, there were no melamine residues in eggs. Following exposure to contaminated feed, cyromazine residue in eggs rapidly reached the maximum on the fourth day after drug administration. When administration was discontinued, elimination of cyromazine was quite fast, about less a week. In egg whites and egg yolks, cyromazine but no melamine was detected on the first day after administration. The residues of cyromazine in egg whites were always higher than egg yolks after administering with cyromazine for fifteen days. Since the seventeen day, the residues of cyromazine in egg yolks exceeded egg whites.