Thymus atrophy is an efficient marker of illicit treatment with dexamethasone in veal calves: Results from a triennial experimental study

Glucocorticoids, used in a wide range of pathologies thank to their therapeutical properties, are also illegally used as growth-promoters in animal breeding even if the European Union regulates their use to protect con- sumers' health from the adverse e ff ects of residues in food. The fi rst aim of the study was to establish the applicability of two histological parameters – atrophy and cortex-medulla ratio - to detect glucocorticoids misuse in calves. The second aim was to concurrently test the potentiality of both parameters to discriminate between treated and untreated animals. One hundred and seventy-two male Friesian veal calves were raised for six months and divided into two groups: Group A (106 calves) was given dexamethasone per os for twenty days (0.4 mg/day), Group B (66 calves) used as control. Thymic samples were microscopically examined. Fat in fi ltration was evaluated and a degree of atrophy, ranging from 1 to 3 (mild, moderate, severe) was attributed; thymic cortex-medulla ratio was calculated too. Fisher's exact test and a Wilcoxon – Mann – Whitney test were performed to investigate the di ff erences in thymic atrophy and cortex-medulla ratio between the groups. Results demonstrate that the thymic atrophy grading was signi fi cantly increased in group A (p = 0,006), whereas the cortex-medulla ratio was decreased (p < 0,004) when compared to group B; moreover, the parallel testing with fi xed degree of atrophy and cortex-medulla ratio cut-o ff thresholds optimize the sensitivity (90%) in the detection of glucocorticoids anabolic treatments. These data suggest that microscopic thymus analysis represent a valid tool for the screening and monitoring of glucocorticoid illicit treatments