Genetic selection for temperament affects behaviour and the secretion of adrenal and reproductive hormones in sheep subjected to stress

Abstract

We investigated the effect of genetic selection for temperament on the way that stressors affect the behaviour and the adrenal and reproductive axes of sheep. We tested three hypotheses: (i) isolation would increase cortisol secretion and decrease luteinising hormone (LH) secretion more in nervous sheep than in calm sheep; (ii) isolation combined with simulated human presence would increase cortisol secretion and decrease LH secretion more in nervous sheep than in calm sheep and (iii) isolation combined with stressors that were not specific to the selection process (i.e. non-selection stressors) would increase cortisol secretion and decrease LH secretion equally in calm and nervous sheep. Isolation alone increased cortisol secretion and decreased LH secretion in nervous sheep but not in calm sheep. Compared to calm sheep, nervous sheep were more agitated during the first 2 h of isolation but not during the second 2 h of isolation. Exposure to non-selection stressors increased cortisol secretion, decreased LH pulse amplitude and the mean plasma concentrations of LH in both calm and nervous sheep. We conclude that genetic selection for temperament affects the behavioural expression of the stress response and the secretion of adrenal and reproductive hormones during isolation, but has less impact on their reactivity to non-selection stressors.

Maternal behaviour and lamb survival: from neuroendocrinology to practical application

“…Beausoleil et al, 2008Beausoleil et al, , 2012 or 'nervous' and 'calm' respectively in other studies (e.g. Bickell et al, 2009;Hawken et al, 2013). Analysis of the behaviour of these flocks in several test situations suggest that consistent behavioural differences exist with one line showing increased activity and vocalisation compared with the other Dwyer in all test situations (Beausoleil et al, 2012).…”

“…Analysis of the behaviour of these flocks in several test situations suggest that consistent behavioural differences exist with one line showing increased activity and vocalisation compared with the other Dwyer in all test situations (Beausoleil et al, 2012). However, the more active sheep in some tests appeared more bold and less fearful than the less active sheep (Beausoleil et al, 2008), and other studies also show no between-flock difference in physiological responses in test situations that were not part of the selection paradigm (Hawken et al, 2013). The most conservative interpretation is that flock variation in activity in specific tests exists, although whether this is related to an emotional response or temperament trait in the animals is not clear.…”

Stress and the Reproductive System

“…198 Further, a combination of psychosocial stress, such as isolation and nervous temperament through genetic selection, resulting in greater cortisol release, suppresses LH pulse frequency when compared to calm sheep. 268 However, the estrous cycle of the ewe appears to be remarkably resistant to disruption by acute episodes of psychosocial stress, whether applied intermittently during a single follicular phase or repeatedly over the course of several estrous cycles. 289 Similarly, repeated exposure to acute psychosocial stress does not disrupt the estrous cycle in pigs.…”

Twenty-four-hour profiles of metabolic and stress hormones in sheep selected for a calm or nervous temperament

“…Interestingly, in horses, the absence of routine and/or hyperreactivity of an individual to the sampling protocol was found to likely result in enhanced cortisol secretion that masks the daily rhythm [48]. Calm and nervous sheep have similar cortisol responses to some novel stressors [44], and so, the reactivity of the individual animals to the change of routine on the day of sampling could have affected their diurnal pattern of cortisol secretion. The incidence and biological significance of a DR in cortisol secretion in sheep require further investigation.…”

“…It is possible that stage of the estrous cycle can affect the diurnal activity of the HPA axis, and for this reason, we chose to maximize our ability to detect a difference in HPA axis activity by eliminating potentially confounding effects and conducting the experiment in anestrous ewes. We conclude that in anestrous ewes selected for temperament, the resting activity of the HPA axis is not affected by the mechanisms that drive the divergence in cortisol secretion in response to the stressors of isolation and novelty [28,43,44].…”