Changes in ear-pinna temperature as a useful measure of stress in sheep (Ovis aries)

Abstract

AbstractActivation of the sympathetic nervous system, with associated increases in heart rate and the redistribution of blood in preparation for ‘fight or flight’, is an integral part of the ‘defence reaction’. In sheep, the defence reaction involves vasoconstriction in the ear-pinna. If decreases in ear-pinna temperature (Tp) can be used to indicate vasoconstriction, then it may be possible to use changes in Tpas a measure of the defence reaction. Ewe lambs were exposed to stressors including mustering into pens, moving between pens, isolation from conspecifics, and prolonged periods of exercise. Measurements of heart rate (HR), Tp, vaginal temperature (Tv), and salivary cortisol and urinary catecholamine concentrations were used to assess stress responses. A repeatable pattern of changes in HR, Tpand Tvwas observed in response to stressors. Short-term disturbances resulted in increased HR, reduced Tp, and increased Tv. More sustained disturbances — for example, prolonged periods of exercise — resulted in a sustained elevation in HR, a sustained decrease in Tp, and a sustained elevation in Tv. The highest levels of cortisol and catecholamines were associated with the treatments that resulted in the longest periods of decreased Tp. We infer that changes in Tpoccur largely in response to changes in sympathetic nervous activity, and that the potential exists to measure elements of stress responses by monitoring Tpin freely behaving animals. This is a minimally invasive measure that allows the monitoring of modest numbers of animals over prolonged periods with minimal handling.