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Cortisol is the primary biomarker associated with the hypothalamic–pituitary–adrenal (HPA) axis. This research aimed at assessing the predictive potential and the relationship of cortisol concentrations in four media (blood, milk, whey and hair) with parity, lactation stage and productive classes. Multiparous (n = 30) and primiparous (n = 38) Italian Mediterranean buffaloes were used and assigned to four productive classes (based on percentiles of mature equivalent milk yield (EMY) and mature equivalent energy corrected milk (eECM)), and cortisol concentrations were measured using a in house radioimmunoassay (RIA) method. Parity did not show a significant effect on cortisol concentrations of the four media. The catabolic stage of lactation (up to 90 d in milk (DIM)) was characterised by higher cortisol concentrations compared to the second anabolic stage (beyond 150 DIM) in milk formulations. The plasmatic concentrations of cortisol were higher at the catabolic and the first anabolic stage (91–150 DIM) compared to the second anabolic (p = 0.022 and p = 0.009, respectively). Buffaloes beyond 150 DIM differed from those below 90 DIM (p < 0.001) and between 91 and 150 DIM (p < 0.05) in hair. Finally, hair cortisol concentrations were negatively correlated to EMY, mature equivalent protein content (EPC) (p < 0.01) and eECM (p < 0.05). The whey showed a potential to predict the concentrations of cortisol in whole extracted milk (R2 = 0.31). Hence the development of a real-time automated cortisol measurement in milk could be a valuable tool in Italian Mediterranean Buffalo farming. HIGHLIGHTS: The lactation stage significantly influences plasma, hair and milk cortisol concentrations. Hair cortisol concentrations are negatively correlated to milk quality parameters. The whey is a potential predictor of the cortisol concentrations in whole extracted milk. [ABSTRACT FROM AUTHOR]