Food Safety 1

Melamine (MEL) may be degraded into cyanuric acid (CYA) and some other analogs by rumen microorganism. This study was conducted to investigate the residue of MEL and CYA in milk and tissues of dairy cows fed with different doses of MEL. Forty mid-lactation dairy cows (157 ± 43 DIM, 20.8 ± 1.4 kg of milk/d) were divided into 4 groups (n = 10/group) in a completely randomized design. The cows of the 4 groups were dosed with MEL (purity ≥99.5%) at 0 (Control), 300 (TRT 1), 500 (TRT 2) and 1000 (TRT 3) mg/d per cow, respectively. The whole trial lasted for 18 d (12 d feeding period, followed by 6 d clearance period). Milk samples were collected at d 1, 2, 3, 4, 8, 12, 13, 14, 15 and 18. On d 13, 3 cows of TRT 2 and TRT 3 were chosen randomly to slaughter, and tissue samples (kidney, liver, mammary, bladder, gluteus medius and longissimus dorsi) were collected. Milk and tissue samples were analyzed for MEL and CYA simultaneously by liquid chromatography tandem mass spectrometry (LS-MS/MS). Minor MEL was detected in concentrated feed background (6.23 ± 1.26 mg/kg), however, no CYA was detected. In MEL treated groups, milk MEL concentration increased quickly and reached a stable concentration at d 4, 8 and 12 after the first administration of MEL. Milk MEL concentration of treated groups in steady-state condition (0.18, 0.27 and 0.50 mg/L for TRT1, TRT2, TRT3, respectively) was significantly affected by MEL feeding dose (P < 0.05), with a linearly relationship between MEL intake and milk MEL concentration (R 2 = 0.91). No CYA was detected in milk of all groups. MEL residue in tissues of TRT 4 was about 2-fold higher than TRT 3, with the highest concentration in the kidney. The difference of CYA residue in tissues of TRT 4 and TRT 3 was not very obvious. Liver, kidney and bladder has higher CYA residue than other tissue. The CYA may come from the degradation of MEL in rumen.