Hair cortisol, dheydroepiandrosterone and progesterone concentrations in crossbred beef cows from calving to 100 days postpartum

Dehydroepiandrosterone (DHEA) and cortisol (C) are hormones secreted by the adrenal cortex after stress stimulation, and they are related to resilience and allostatic load. Hair steroids measurement has recently received increasing attention for measurement of chronic stress in dairy cows, as it offers the advantages of being noninvasive, fast, and able to indicate steroids levels over long periods [1]. Around the time of calving, cows experience a suite of stressful events, including regrouping, diet changes, parturition, and the onset of lactation; during the transition period, it has been demonstrated that primiparous cows behave differently and are more likely to experience negative health outcomes compared to multiparous cows [2]. The objects of this study were to evaluate C, DHEA and progesterone (P4) hair concentrations in crossbred beef cows from calving to 100 days post partum (pp), and to assess possible differences related with parity (primiparous vs multiparous cows). Six primiparous and five multiparous pregnant beef cows from a tethered stall were enrolled. Hair samples of the 11 cows were collected during the autumn/winter season by shaving at calving (T0) and every 20 days for five times (T1-T5), only on the re-growth area. Hair C, DHEA and P4 were analyzed by RIA [1]. No differences were detected in the hair re-growth among animals. Statistical analysis showed higher C concentrations in primiparous cows at calving (T0) and at 20 days pp (T1) compared to all the subsequent samples (p<0.05). C levels at T0 and T1 in primiparous cows (6.7±3.37 pg/mL and 7.9±3.16 pg/mL, respectively) were higher than in multiparous cows (4.2±3.76 pg/mL and 4.1±2.36 pg/mL, respectively) (p<0.05). No other differences were detected within each group or between the two groups of cows regarding C, DHEA and P4 concentrations. These results suggest that C hair concentrations in cows are affected by parity. The higher C levels registered at calving and at 20 days pp in primiparous cows indicate a greater stress level before and around parturition compared to multiparous cows. Considering that the animals enrolled in this study did not undergone major changes of management or diet, this difference is probably related with the fact that calving was experienced for the first time by the pregnant heifers. Cortisol levels did not change from sample T2 (40 days pp) to the end of the study, suggesting the capacity of the heifers to recover from calving stress. Similarly, pluriparous cows did not show any relevant increase in C levels around calving, possibly because of their resilience. DHEA and P4 hair concentrations were not affected by parity neither by time; both these hormones are secreted also by the placenta in the pregnant cow [3], so the concentrations observed in their hair also derives from a placental synthesis. The present study suggests that hair C can be useful for measurement of the allostatic load in cows, and that primiparous cows undergo a higher stress level around calving compared to multiparous cows.