Assessing significant (>30%) alopecia as a possible biomarker for stress in captive rhesus monkeys (Macaca mulatta)

Hair loss is common in macaque colonies. Very little is known about the relationship between psychological stress and hair loss. We initially examined alopecia and hair cortisol concentrations in 198 (89 male) rhesus macaques from three primate centers and demonstrated replicability of our previous finding that extensive alopecia (>30% hair loss) is associated with increased chronic cortisol concentrations and significantly affected by facility. A subset of these monkeys (142 of which 67 were males) were sampled twice approximately 8 months apart allowing us to examine the hypotheses that gaining hair should be associated with decreases in cortisol concentrations and vice versa. Hair loss was digitally scored using ImageJ software for the first sample. Then visual assessment was used to examine the second sample, resulting in three categories of coat condition: (i) monkeys that remained fully haired; (ii) monkeys that remained alopecic (with more than 30% hair loss); or (iii) monkeys that showed more than a 15% increase in hair. The sample size for the group that lost hair was too small to be analyzed. Consistent with our hypothesis, monkeys that gained hair showed a significant reduction in hair cortisol concentrations but this effect only held for females. Coat condition changed little across sampling periods with only 25 (11 male) monkeys showing a greater than 15% gain of hair. Twenty (7 male) monkeys remained alopecic, whereas 97 (49 males) remained fully haired. Hair cortisol was highly correlated across samples for the monkeys that retained their status (remained alopecic or retained their hair). Am. J. Primatol. 79:e22547, 2017. © 2016 Wiley Periodicals, Inc.