Evaluation of nandrolone and ractopamine in the urine of veal calves: liquid chromatography-tandem mass spectrometry approach.

Under European legislation, the use of growth promoters is forbidden in food-producing livestock. The application of unofficial protocols with diverse combinations of veterinary drugs, administered in very low concentrations, hinders reliable detection and subsequent operative prevention. It was observed that nandrolone (anabolic steroid) and ractopamine (ß-adrenergic agonist) are occasionally administered to animals, but little is known about their synergic action when they are administered together. Two specific analytical methods based on liquid chromatography-tandem mass spectrometry have been developed, both of which include hydrolysis of the corresponding conjugates. For the nandrolone method, solid-phase extraction was necessary for the complete elimination of the interferences, while employment of the Quantitation Enhanced Data-Dependent scan mode during MS acquisition of ractopamine enabled the utilization of simple liquid-liquid extraction. The nandrolone method was linear in the range of 0.5-25 ng/mL, while the ractopamine calibration curve was constructed from 0.5 to 1000 ng/mL. The corresponding coefficients of correlations were >0.9907. The lower limit of quantification for both methods was 0.5 ng/mL, followed by overall recoveries >81%. Precisions expressed as relative standard deviations were <17%, while matrix effects were minimal. Urine samples taken at the slaughterhouse from veal calves enrolled in an experimental treatment consisting of intramuscular administration of ß-nandrolone-phenylpropionate accompanied with a ractopamine-enriched diet were analysed. Those methods might be useful for studying the elimination patterns of the administered compounds along with characterization of the main metabolic pathways. Copyright © 2016 John Wiley & Sons, Ltd.

Thymus atrophy and regeneration following dexamethasone administration to beef cattle.

Thymus atrophy and regeneration were studied in 13- to 22-month-old beef calves treated with dexamethasone (DMT), using anabolic dosages and implementing different withdrawal times. Two trials were conducted. In trial 1, group A (n=6) received 0.7 mg/day DMT orally for 40 days, group B (n=6) received 1.4 mg/day orally for 40 days and group C (n=6) was the control. In trial 2, group D (n=6) received 0.7 mg/day DMT orally for 40 days, group E (n=6) received 1.4 mg/day orally for 40 days and group K (n=6) was the control. DMT withdrawal times before slaughter were six days (groups A and B) and 26 days (groups D and E). At slaughter, thymus atrophy was severe and progressive in animals from groups A and B. In contrast, thymus weight and volume of the animals from groups D and E were almost normal. Slight atrophy was also detected in the calves in these groups. Histological changes and Ki67 immunostaining revealed a large number of positive lymphoid cells, mostly in the cortical area, associated with higher expression of apoptosis in the medulla compared with controls. This demonstrated that the thymus of beef cattle is still able to regenerate following DMT administration.