The Accumulation And Depletion Of ?-agonists In Beef Cattle

In this paper,we studied the effects on plasma parameters,internal hormone level and the accumulation and depletion of ?-agonists(ractopamine,clenbuterol and salbutamol)with oral administation of low dose cocktails in beef cattle for providing technical support on supervising illegal use of ?-agonists in beef cattl.A total of 18 healthy Simmental cattle with a similar body weight(BW)257.9±33.3 kg were randomly divided into three groups.Cattle were fed with the same basal diet,animals from the test group ? were daily treated with 670.0?g/kg BW ractopamine while the test group ? were daily treated with a mixture of ractopamine,salbutamol and clenbuterol(223.3?g/kg BW,50.0?g/kg BW and5.3?g/kg BW,respectively)for 28 consecutive days and withdrawal time is 84 days.Determing samples include plasma and urine samples on treatment day 1,7,14,21,28 and withdrawal day 3,7,14,28,42,hair samples on treatment day 1,7,14,28 and withdrawal day 14,28,42,84.Trial one: Determing samples include plasma samples on treatment day 28 and withdrwal day 28.Concentrations of GLU,FFA,GH,INS and IGF-1 were determined.The results showed that(1)at treatment 28 d,plasma FFA concentrations were lower significantly in test groups ? and test groups ? than control group(P<0.05)while at withdrawal 28 d,its concentrations were showed no difference between test group and control group.These results demonstrated that plasma FFA concentrations which can be used as potential biomarkers to supervise the illegal use of ?-agonists,were significantly affected by ?-agonists with the two feeding modes.(2)Plasma hormone levels were not significantly affected by?-agonists at the whole test process.Trial two: Determing samples include plasma,urine and hair samples at every treatment and withdrawal time.Residues of ractopamine,salbutamol and clenbuterol in all samples were determined using ultra-high performance liquid chromatography tandem mass spectrometer(UPLC-MS/MS).The results indicated that(1)The residues of three ?-agonists in plasma increased gradually to peak during treatmenttime,0-3 d after treatment,its residues have a rapidly decreasing trend,then decreased slowly.Residues of ractopamine and salbutamol after hydrolysis were higher significantly than before(P<0.05),the peak plasma concentration were43.78 ng/mL,1.49 ng/mL and 8.07ng/mL respectively.(2)The residues and depletion of three ?-agonists in urine was similar to plasma,after enzymolysis treatment,the residues also showed increasing trend than before and the peak urine concentration were 3995.77 ng/m L,58.36 ng/mL and 478.61 ng/mL respectively.(3)The residues and depletion of ractopamine,salbutamol and clenbuterol in hair showed a high similarity.the peak time all presented at withdrawal 7-14 d and peak hair concentration were 3995.77 ng/mL,58.36 ng/mL and 478.61 ng/mL respectively,then started to decrease and still higher than the limit of quantitation at withdrawal84 d.(4)Compared with plasma and urine samples,hair samples have more advantages such as higher accumulation of three ?-agonists and longer depletion time.So,hair is an appropriate target to supervise the abuse of low-dose ?-agonists in beef cattle.In general,the results of this study demonstrate that concentrations of plasma FFA were significantly lower than control in both the feeding modes and residues of the three ?-agonists in cattle hair could be a more useful matrix for supervising.These provided some technology and expanded the scope of monitoring the illegal use of ?-agonists.