Effect of season of collection and storage method on equine hair cortisol concentration

Serum cortisol concentration is one of the common physiological reference standards for evaluating stress in animals. However, it only evaluates acute stress at the moment of blood collection. Hair cortisol concentrations (HCC) could provide a method for assessing cortisol concentrations over extended periods of time, giving an estimate of chronic stress levels. In this case, high HCC results could help equine managers alter management practices to improve welfare.

To evaluate the effect of the month of collection and the storage method on equine HCC.

Tail hair was collected from 32 mature horses in February and August of the same year, both times from the same location. Samples were split and packaged in resealable plastic bags, with half stored in a cardboard box in a climate-controlled environment at 21.1°C (ROOM) and the other half stored in a freezer at -20°C (FROZEN). February collections were stored for eight months before analysis, while August collections were stored for two months.

FROZEN samples had higher HCC (P = 0.0278), as did August samples (P = 0.0067), but there was no significant interaction between storage method and month of collection. It is likely that higher HCC in August were the result of horse exposure to longer daylight hours.

Results from this study suggest that storing hair samples in a frozen state will better preserve cortisol concentrations.