Immunohistochemistry by anti-cleaved-Lamin A: an improved approach to tackle the misuse of glucocorticoids in cattle.

The illegal use of glucocorticoids (GCs) as growth-promoters (GPs) is prohibited in farm animals in the European Union because the strong pharmacological activity of most synthetic GCs produces residues that are dangerous for human consumption. Among the alternative methods proposed to increase the efficacy of official controls, histology was the technique of choice in Italy on account of its high performance level. The aim of this study was to evaluate the reliability of immunohistochemistry (IHC) using anti-cleaved-Lamin A antibody to enhance the performance of the histological test applied to GC-related microscopic changes in the thymus. Veal calves (VC) and beef cattle (BC) were raised and both underwent different growth-promoting protocols or were left untreated. The morphology of the thymus parenchyma was evaluated for cortical atrophy with concurrent adipose tissue infiltration, and a score of 1 to 3 was attributed. A semi-quantitative IHC analysis was also performed by counting the number of positive thymocytes in 5 randomly selected high-power fields (HPFs). The distribution of the thymus atrophy scores was significantly different among the subgroups in both BC and VC. The IHC values were higher in untreated than in treated animals, for both BC and VC. The association between thymus atrophy score and IHC positivity showed higher median values in control than in treated animals (independently of the treatment protocol), for both BC and VC. Our data shows that IHC against anti-cleaved-Lamin A antibody is a reliable marker to detect illegal GC treatments, administered either alone or in association with other growth promoters, in both BC and VC. Combining IHC with the thymus atrophy score improves the accuracy of the histological method in correctly identifying treated animals and could represent a valuable, reproducible method to be applied to large-scale screening programmes.