To investigate the tissue deposition and elimination of melamine (MEL) in broilers, a total of 1 920 commercial 1-d-old male Cobb broilers were randomly allotted to 6 treatments with diets contaminated by MEL at 0, 2, 10, 30, 50, 100 mg kg-1 of diet for 42 d, and followed MEL withdrawal from diet at 50 or 100 mg kg-1 of diet for 96 h. The MEL was found in residue of plasma, liver, kidney, breast, and leg muscle with the highest level in kidney and in dose response manner (except in kidney), but no time response (except in plasma). The MEL residue in organ tissue was below the safe level of 50 μg mL-1 in blood or 50 μg kg-1 in tissues proposed by the US FSIS when MEL in diet was lower (2 mg kg-1). The MEL in tissues was eliminated by withdrawal MEL from diets. The elimination half-life of MEL was from 3.2 to 6.6 h, and the clearance time, when MEL residue concentration under limit detection, was from 18.0 to 31.4 h.

An experiment was conducted in a singly factorial design to study the effect of glycyl-glutamine dipeptide on enzymeactivity, cell proliferation and apoptosis of jejunal tissues from weaned piglets at different glycyl-glutamine concentrationlevels of 2, 4, 10, 20, and 30 mmol L-1, respectively. The glutaminase activity, diamine oxidase (DAO) activity, cellpeoliferation, apoptosis, and perotein metabolism were measured by the tissue culture method in vitro using jejunaltissues. The immunohistochemical method was used to study the cell proliferation and apoptosis of jejunal tissues. Theresults showed that compared to the blank control, the percentage and MOD value of BrdU-positicve cells incubated withglycyl-glutamine dipeptide solution were significantly (P<0.05) increased. Accordingly, the percentage and MOD valueof caspase-3-positive cells from tissue incubated with glycyl-glutamine dipeptide were notably lower (P<0.05) than thatfrom the control treatment. The glycyl-glutamine dipeptide increased the glutaminase activity, DAO activity and proteincontent of jejunal tissues, as the dipeptide concentration was on the rise (P<0.05). These results indicated that glycylglutaminedipeptide affected the jejunum development and adaptation of weaned piglets, and the function might befulfilled by enhancing the glutamine-related enzyme activity, thereby increasing the consumption of glutamine, and thenimproving the jejunal cell proliferation and suppressing cell apoptosis. The effects of glycyl-glutamine dipeptide relied ina dose-dependent manner, and the maximum effect was achieved at 20-30 mmol L-1 glycyl-glutamine dipeptide.