Measuring cortisol in hair and saliva from dogs: coat color and pigment differences

Cortisol concentrations are frequently measured from a variety of sources including blood, saliva, urine, and feces to quantify stress in dogs. However, a need still exists for less intrusive collection methods in domestic animals and for more efficient means of measuring basal cortisol. The objectives of the present study were to minimize restraint for saliva sampling, to validate hair for basal cortisol measurement in dogs, and to determine concentrations of cortisol within the hair shaft and in relation to hair color. Using food luring, 79% of dogs required no restraint for saliva collection. Salivary and hair cortisol concentrations were positively correlated (P = 0.001), thus validating hair as a medium for basal cortisol quantification. Black dogs had less cortisol than nonblack dogs (P = 0.039) in hair, but not saliva. Across dogs, the average amount of cortisol did not differ between proximal and distal hair sections (P = 0.348). However, for 7 of the 9 dogs, more cortisol was present in the distal portions of the hair. We observed a difference in cortisol concentrations among hairs of different colors from individual dogs (P = 0.001). From the same 7 x 7 cm ischiatic patch from the same dog, black (eumelanin) hairs were consistently lower in cortisol than yellow (pheomelanin) hairs, and cortisol concentrations of agouti hairs were intermediate. This is the first evidence that hair of different colors might sequester cortisol differently.