Preliminary study on the presence of prednisolone in porcine urine and liver - How to distinguish endogenous from therapeutically administered prednisolone.

In animal breeding in Europe, synthetic corticosteroids are not allowed as growth-promoting agents. However, prednisolone residues have recently been found in porcine urine samples collected at slaughterhouses. The aim of this work was therefore to look for prednisolone in porcine urine and liver, to determine if detected residues might be of endogenous origin, and to check the possible relation with stress. An analytical method developed in-house was validated, combining immunoaffinity-based purification and ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). This method was applied to urine and liver samples collected from sows experimentally treated either with prednisolone or tetracosactide hexaacetate (synthetic analogue of ACTH). Thanks to the performance of the analytical method, both cortisol and prednisolone were detected in all pig urine samples collected before or after administration of prednisolone or tetracosactide hexaacetate. High levels of prednisolone were found in porcine urine just after prednisolone administration, decreasing quickly to within the range detected in non-treated animals. In urine, the cortisol level varied depending on the time lapse between administration and sampling. On the other hand, prednisolone was detected also in liver samples of treated pigs. In this matrix, the cortisol level remained constant and prednisolone/cortisol level could be used to detect prednisolone administration at least 4 days after injection. In conclusion, the best indicator for detecting illicit prednisolone administration to pigs seems to be the prednisolone/cortisol ratio in liver samples. This preliminary work must be confirmed by a larger-scale study and metabolites should also be included.