Carry-over of melamine from feed to eggs and body tissues of laying hens

Abstract

The objective of this study was to assess the carry-over of melamine from feed into eggs and body tissues of laying hens. In the first experiment, laying hens were supplied with feed added at 0, 1, 2, 5, 25, 50, and 100 mg kg(-1) of melamine for 21 days followed by a depletion period to observe the residues of melamine in eggs. In a second experiment, laying hens were allocated 0, 50, and 100 mg kg(-1) melamine to determine levels of melamine in body tissues. Melamine and cyanuric acid were simultaneously analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the diet as well as in eggs and body tissue. In the first experiment, melamine appeared in the egg within 24 h after first ingestion of the melamine at 5, 25, 50, and 100 mg kg(-1). Melamine concentration in egg reached a maximum of 2.34 mg kg(-1) within 17 days after exposure of 100 mg kg(-1) melamine, and the carry-over rate for melamine from feed to the eggs was 1.21%. In the second experiment, melamine was detected in tissues within 3 days after exposure; the maximum concentration of melamine residues occurred in the 100 mg kg(-1) group and was as follows: egg (1.83) > kidney (1.21) > breast muscle (0.86) > liver (0.70) > serum (0.42). The melamine level in egg albumen was about twice that of egg yolk. Melamine levels in laying hens decreased rapidly with withdrawal from feed, but melamine only declined to undetectable levels in the egg at day 6 and in tissues at day 4 after last ingestion of 100 mg kg(-1). It can be concluded that a pathway exists for the transmission of melamine from feed to egg and body tissues and the carry-over rate of melamine is low, and that melamine is not metabolized into cyanuric acid in laying hens. A positive relationship exists between exposure levels and eggs or tissues, but no direct relationship between the exposure time and measured levels of melamine in eggs and tissues. The current Chinese limit for melamine in feed and feed material of 2.5 mg kg(-1) established on 8 June 2009 is sufficient to ensure that levels in eggs, breast muscle, liver as well as kidney will not exceed the limit of 2.5 mg kg(-1) in foods other than infant formula introduced by many countries including China.