Cardiac frequency: a potential predictor of blood cortisol levels during acute and chronic stress exposure in Rocky Mountain bighorn sheep (Ovis canadensis canadensis)

It was the purpose of this study to investigate methods of assessing responses to stress by free-ranging bighorn sheep (Ovis canadensis canadensis). The adrenal response test on wild-caught bighorn sheep maintained in captivity did not demonstrate either adrenal exhaustion or hypersensitivity during chronic stress. To study physiological responses to acute stress, hand-reared bighorn sheep were habituated to living in stalls and fitted with electrocardiogram leads and jugular cannulas for remote monitoring of cardiac frequency and blood cortisol changes. A radioimmunoassay was validated on bighorn sheep plasma which was a modification of the procedure used for domestic sheep. A linear relationship between heart rate and blood cortisol was obtained for individual animals suggesting that remote monitoring of cardiac frequency can be used as a predictor of adrenal function and, therefore, the potential immunologic condition of an animal during stress.