A LC-MS-MS method to detect recombinant bovine somatotropin misuse in buffalos

Recombinant bovine somatotropin (rbST) is a peptide hormone used to increase milk yield in cows and buffalos. In Europe, its use has been banned. However, rbST is sometimes illegally included in zootechnical practices for profit purposes, undermining the fair trade and the law prescriptions. For this reason, efficient and reliable analytical techniques are required to contrast rbST misuse. A few LC-MS-MS methods have been developed to detect, in cow serum, methyonil-rbST, one of the two main rbST forms available on the market. The other form, which is widespread, is identical to the most abundant variant of bovine somatotropin (bST) and differs from the buffalo somatotropin for one amino acid in the N-terminus. For this reason, it is technically possible to distinguish both rbST forms in serum of buffalos. In this work, we describe a novel LC-MS-MS-based method, capable to quantify, with a high sensitivity and selectivity, the methyonil-rbST and the other bST-identical recombinant form in buffalo serum, previously purified using a solid-phase extraction procedure. The method was internally validated and used to analyse 152 serum samples, collected from eight buffalos administered with rbST for a period of 3 months, according to conventional protocols. The obtained results confirmed the suitability of the method in the detection of illegal hormonal treatments.