Determination of natural progesterone levels in bovine serum using gas chromatography coupled with mass spectrometry.

Introduction: Progesterone, a steroidal female sex hormone, can be used for anabolic purposes in cattle. Physiological levels of progesterone in animals are highly variable, and systematic studies of them in various matrices are limited. The purpose of the present study was to apply a developed and validated method routinely used for the determination of the natural hormones 17β-oestradiol and 17β-testosterone in serum to estimate natural cattle progesterone levels. The analytes were taken from serum samples collected from cattle as part of the Polish National Residue Control Plan. Material and Methods: A total of 1,537 bovine serum samples were analysed: 895 from females and 642 from males. Progesterone was extracted from serum with a mixture of tert-butyl methyl ether and petroleum ether, the extract was derivatised and the analyte was determined by gas chromatography coupled with mass spectrometry. Results: The basic validation parameters specified for the method, namely repeatability, reproducibility and apparent recovery, indicated it to be useful for the intended purpose. The natural presence of progesterone was detected in 679 samples from females and in 375 samples from males. Progesterone in females was measured in the range of 0.001-496.059 μg L-1 (in 61% of samples it was below 1 μg L-1 and in 32% it was in the range of 1-7 μg L-1, which are the physiological ranges of phases of the reproductive cycle) and progesterone in males was assayed in the range of 0.001-31.792 μg L-1. Conclusion: The results obtained may serve as a statistical basis for further research.