Recombinant bovine somatotropin misuse in cattle: Evaluation of Western blotting and 2D electrophoresis methods on biological samples for the demonstration of its administration

Abstract

Somatotropins (growth hormone, GH) which are used in cattle for growth and lactating performances are difficult to reliably detect since no direct method exists. Until now, the detection of GH in bovine milk, plasma and tissue has been based on radioimmunoassays and enzyme-linked immunosorbent assay (ELISA) tests that are unable to distinguish between endogenous and recombinant hormones. Attempt to directly detect recombinant GH administration is an analytical challenge which has never been successfully reported. The aim of the present work was to develop an original method, based on the detection in serum of antibodies raised against growth hormones as a consequence of their administration to animals. A second approach was developed with the characterisation of recombinant bovine somatotropin (rbST) in milk through the use of two-dimensional electrophoresis coupled to in-gel tryptic digestion followed by tandem mass spectrometry coupled to liquid chromatography (LC-ESI-MS/MS) measurements of the produced peptides. Results obtained showed the relevance of the two approaches. The Western blot one, carried out in this work on real biological blood samples collected on treated animals, would fit as a rapid and rather sensitive screening method, which can further more be achieved more over a long period after the administration of recombinant hormone. The second method, which consisted in a proteomic approach, dealt with the development of a confirmatory technique. Results on spiked milk samples were very promising and showed the need of further developments in this way.