Development and validation of an enzyme-linked immunosorbent assay for the detection of circulating antibodies raised against growth hormone as a consequence of rbST treatment in cows.

The recombinant bovine growth hormone (rbST) is used to increase lactating performances of dairy cows. Administration of rbST is banned in the European Union; nevertheless, its use is probable. Until now, efficient analytical strategies to detect such practice are based on the direct detection by mass spectrometry of the presence of rbST in biological fluids, which suits for confirmatory purposes. Current screening strategies do not offer satisfactory performances; therefore, alternative screening strategies are required. The aim of the present work is to develop and validate an ELISA to measure the production of specific antibodies upon rbST in bovine sera. In this immunoassay, rbST is absorbed onto microtiter plate. After specific purification of the antibodies in serum, samples are analysed and the presence of antibodies anti-rbST is detected by Protein G peroxidase conjugate and 2-2'-azino di-ethyl benz-thiazoline-6-sulphonic acid (ABTS). The mean reproducibility of the OD (λ=405 nm) measurement was calculated with a CV of 13%. The intra- and inter-assay CVs ranged from 0.79% to 7.91% and from 2.69% to 20% respectively. The test presents cross-reaction with other growth hormones such as the recombinant equine (reST) and porcine (pST) (100% and 80% respectively). The specificity of the test toward rbST anabolic treatment was confirmed through the analysis of sera samples collected on animals administered with other anabolic compounds (steroids). The performances of the present anti-rbST ELISA proves its efficiency as a new screening tool to highlight illegal administration of rbST in cattle up to at least 3 weeks after treatment.