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

[Display omitted] •Stressed piglets gained significantly less weight than controls between 7 and 28 days of age.•Hair from the stressed group contained significantly higher concentrations of cortisol than hair from controls.•Salivary cortisol concentrations did not differ significantly between stressed and control groups at Day 28.•Weight gain was significantly and negatively correlated with hair cortisol concentrations in the stressed group after 3 weeks.•Weight gain and hair cortisol concentrations did not correlate with salivary cortisol concentrations at Day 28. 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 (0.10m2/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 0.29m2/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).