A Procedure for Oxytocin Measurement in Hair of Pig: Analytical Validation and a Pilot Application

SIMPLE SUMMARY: Oxytocin is gaining importance in human and animal studies because of its role in welfare stress response, but there is no evidence of oxytocin measurement in hair, which would allow an evaluation of this analyte over a long period of time. For this reason, in this study, a new immunoassay to measure oxytocin in the hair of pigs was developed and validated. In addition, the possible changes in concentrations of oxytocin in hair during the reproductive cycle of pigs were evaluated. The assay was precise and accurate and when applied to the hair extracts of pigs, higher oxytocin values were obtained at days 23 and 59 after farrowing in the winter–spring period. When oxytocin concentrations were compared to cortisone and cortisol, it showed moderate and low correlations, respectively. Based on the results of this report, oxytocin can be measured in the hair of pigs, and changes in concentrations can be detected during a pig’s reproductive cycle. ABSTRACT: There is growing interest in oxytocin as a biomarker of stress and welfare. The objective of this study was to develop and validate a procedure based on a highly sensitive immunoassay to measure oxytocin in the hair of pigs. In addition, a pilot study to apply this procedure to evaluate possible changes in concentrations of oxytocin in hair during the reproductive cycle of pigs at different periods of the year was conducted. This procedure used methanol for sample extraction, since it offered better recoveries than acetonitrile, and the immunoassay developed was precise and accurate for the quantification of the oxytocin in the hair. When this procedure was applied to hair collected at different times of the reproductive cycle and season, higher values were found at days 23 and 59 after farrowing in the winter–spring period. In addition, higher oxytocin values in the spring–summer period were found in hair collected 5 days before farrowing compared to winter–spring. Oxytocin in hair showed moderate and low correlations with cortisone and cortisol in hair, respectively. This study represents the first report in which oxytocin was measured in hair and could open new lines for future research about the measurement of oxytocin in pigs and other biological species as a biomarker of stress.