Hair or salivary cortisol analysis to identify chronic stress in piglets?

Hair cortisol might better represent chronic stress than salivary cortisol in piglets. To test this hypothesis, 24 female, 7-day old piglets were allocated to two groups and artificially reared. The piglets in the stressed group were exposed to overcrowding (0.10m/piglet) and frequent mixing with unfamiliar piglets until the age of 28 days. The control group remained in an unchanging group at a density of 0.29m/piglet. After 3 weeks, stressed animals had gained significantly less weight (median, here and throughout, 7.58kg) than the control animals (6.43kg; P=0.021). Additionally, hair from the stressed group contained significantly higher cortisol concentrations (87.29 vs. 75.60pg/mg hair; P=0.005), whereas salivary cortisol concentrations did not significantly differ between groups (0.30 vs. 0.25 μg/dL saliva; P=0.447). Weight gain and hair cortisol concentrations were significantly correlated (P=0.036, r=-0.430), but neither of these parameters were correlated with salivary cortisol concentrations (P=0.929, r=0.019 and P=0.904, r=0.026, respectively).