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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 (0.10 m²/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 0.29 m²/piglet. After 3 weeks, stressed animals had gained significantly less weight (median, here and throughout, 7.58 kg) than the control animals (6.43 kg; P = 0.021). Additionally, hair from the stressed group contained significantly higher cortisol concentrations (87.29 vs. 75.60 pg/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 …