| This study was conducted to investigate the deposition and metabolism of melamine in finishing pigs and its toxicity to the kidney of finishing pigs. The results could provide data for the supervision of this verboten feed additive, ensuring the safety of consuming the pork and pork products.Experiment 1 Residue and Depletion of Dietary Melamine in Tissues and Plasma of Finishing PigsThirty-six crossbred pigs were administrated with 500 mg or 1,000 mg per kg diet for 42 days as the melamine deposition stage, then melamine was withdrew from the diet for 5 days as the depletion experiment. Blood samples were collected at days 14,28 and 42. Another six pigs were selected to for the establishing of the dynamic clearance model of melamine in plasma. The six pigs were administrated with feed containing 1,000 mg/kg melamine for 42 d. On day 42 and the six pigs were fed with 1 kg of the experimental feed, blood samples were collected at the 0,2,4,8,12,24,48 and 72 h after the intake of the diet. The melamine concentration in all samples were determined by LC-MS/MS. Results showed that growth performances (feed intake, daily gain and feed efficiency) did not differ among all the treatments during the deposition experiment(P> 0.05). The concentrations of melamine in kidney, muscle, liver, brain, heart and duodenum were in the range of 0.04-5.61μg/g, 0.02-2.80 ug/g,0.03-2.58μg/g, N.D.-2.56μg/g,0.02-2.52μg/g and 0.02-2.55μg/g, respectively. ays 5 days after the withdrawal of melamine from the diets, melamine residue in tissues of finishing pigs decreased quickly to the below 2.5 mg/kg. However, as the melamine concentration increasing in the tissues, the melamine was more difficult to clear. Significant negative correlation existed between melamine concentration and time(r=-0.799,P<0.0001). Melamine concentration in plasma would reach the peak 4 h after the intake of melamine-contaminated diet. After 42 days intake of feed containing 1,000 mg/kg melamine, the exponential model could be used to imitate the clearance of melamine in plasma of finishing pigs. The regression equation was Y= 14.6327* e(-0.1152X)(R2=0.994, P< 0.0001). Experiment 2 Effect of Dietary Melamine on Kidney Structure and Function of Finishing PigsOn the basis of experiment 1. blood samples were collected at days 14.28 and 42 to determine the glutamic-oxalacetic transaminases (GOT) and glutamic-pyruvic transaminase activity (GPT), serum creatinine (SCr)and cystain-C (Cys-C) concentration in them. On days 42 and 47, the left kidney was collected to observe the pathological changes. Results showed that the administration of melamine (1,000 mg/kg) made the GPT activity and SCr concentration increasing significantly on days 28 and 42, respectively. However, no obvious effect was observed on Cys-C concentration. The melamine addition in the feed would lead to obvious pathological changes in renal tubules and renal interstitial, and after the 5 days clearance experiment, the lesion of kidney structure could not recover.The two experiments showed that the addition of melamine in feed have no obvious effect on the performance of finishing pigs. However, melamine would residue in tissues and plasma of finishing pigs, and the residue concentration rose with the melamine concentration increasing in feed. The addition of melamine in the feed slightly hurt the kidney of finishing pig, but the renal failure did not occur.5 days after the withdrawal of melamine from the diet, melamine concentrations in tissues of finishing pigs fell to below 2.5 mg/kg. After 42 days intake of feed containing 1,000 mg/kg melamine, the exponential model could be used to imitate the clearance of melamine in plasma of finishing pigs. The regression equation was Y=14.6327* e(-0.1152X)(R2=0.994, P< 0.0001). According to this equation, after 42 days intake of feed containing 1,000 mg/kg melamine, it need 15.3h for the residual melamine declining to the limitation of 2.5μg/mL. |
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