LC-MS/MS analyses of bile and histological analyses of thymus as diagnostic tools to detect low dose dexamethasone illicit treatment in beef cattle at slaughterhouse

Dexamethasone (DXM) is a synthetic adrenal corticosteroid with anti-inflammatory properties used for therapeutic purposes in a wide range of pathologies and of the most common corticosteroids used for anabolic purposes in beef cattle. It is proven that DXM induces histological changes, traceable as increasing fatty infiltration of the thymus associated with a concurrent decrease of the cortex-medulla ratio, so the histological examination of the thymus gland has been established as an indirect morphological biomarker. The aim of the present study is to compare thymus histology and DXM concentrations in biological fluids collected at slaughterhouse after 1 month of DXM treatment. Our findings demonstrate that a low dosage of DXM administered to 12 months-old-Chianina beef cattle induces severe thymic atrophy with concurrent reduction of the cortex/medulla ratio, demonstrable even when DXM residues are not found in serum and urine samples. It is worth to note that, at the slaughterhouse, DXM residues are detectable in bile samples, indicating the ability of this biological fluid to bio-concentrate the administered drug if compared to serum and urine. Therefore, bile could be candidates as new liquid matrix for the screening programs planned to contrast the illegal use of anabolic substances.