Search

There is increasing interest in using nonblood measures of glucocorticoids to assess the physiological response to chronic stress conditions. In sheep, cortisol has been measured in various matrices including saliva, feces, and wool, but comprehensive studies of the relationship between plasma concentrations of cortisol and concentrations in these nonblood matrices are lacking. Therefore, we tested the hypothesis that administration of cortisol to sheep would result in elevated concentrations of cortisol in blood, saliva, feces, and wool. Merino ewes were administered with saline or 2 mg/kg BW/d hydrocortisone acetate (HCA) by intramuscular (i.m.) injection for 28 d. This treatment was imposed to mimic circulating cortisol concentrations experienced during periods of chronic stress. Cortisol and cortisone were directly measured in plasma, saliva, and wool before, during, and after treatment with saline or HCA. A 14-d pre-treatment and a 14-d post-treatment period were used to measure time taken for glucocorticoid concentrations in each of the matrices to return to baseline levels. Cortisol was also measured in feces before, during, and after treatment. Wool growth was also measured. Before treatment, there was no difference in the concentration of cortisol or cortisone in plasma, saliva, feces, or wool in animals treated with saline or HCA. In contrast, treatment with HCA increased (P < 0.05) concentrations of both cortisol and cortisone in plasma, saliva, and wool and of cortisol in feces. In plasma, cortisol concentrations were higher than cortisone (P < 0.05), whereas saliva cortisol and cortisone concentrations did not differ significantly. In wool, the concentration of cortisone was about 19-fold higher than that of cortisol during treatment and post-treatment periods. Treatment with HCA inhibited wool growth. These results demonstrate that an increase in glucocorticoids in the blood of sheep is reflected in increases in saliva (after 7 d of treatment), feces (21 d), and wool (14 d). Therefore, measures of glucocorticoids in these matrices may provide a measure of activation of the adrenal glands over time in sheep, thereby providing a retrospective indicator of chronic stress. With respect to wool, it appears that cortisol is predominantly metabolized to cortisone in the skin or wool follicle and is stored as cortisone. Therefore wool cortisone may also provide an important measure in quantifiying chronic stress in sheep.

Activation of the hypothalamo-pituitary-adrenal (HPA) axis by psychosocial stress is attenuated during lactation. We tested the hypothesis that lactating ewes will have attenuated HPA axis responses to isolation and restraint but will have greater responses to predator stress in the form of barking dogs. We imposed two 4 h stressors: psychosocial stress (isolation and restraint of ewes) and predator stress (barking dogs). Blood was collected intravenous every 10 min from nonlactating ewes (n = 6), lactating ewes with lambs present but not able to be suckled (n = 6), and lactating ewes with lambs present and able to be suckled (n = 6). Plasma cortisol and oxytocin were measured. For nonlactating ewes, cortisol increased (P < 0.01) in response to both stressors, and these increases were greater (P < 0.01) than that in the lactating animals. For lactating ewes with lambs present but unable to be suckled, cortisol increased (P < 0.05) in response to both stressors with a greater response to barking dogs (P < 0.05). For lactating ewes with lambs present and able to be suckled, cortisol increased (P < 0.01) in response to barking dogs only. Plasma oxytocin was greater (P < 0.01) in lactating ewes than in nonlactating ewes and did not change in response to the stressors. In conclusion, lactating ewes are likely to have a greater HPA axis response to a stressor that may be perceived to threaten the welfare of themselves and/or their offspring. The role of oxytocin in attenuation of the HPA axis to stress in sheep is unclear from the current research and requires further investigation., Highlights • The response of the hypothalamo-pituitary-adrenal axis to stress is attenuated during lactation in sheep. • The extent of this attenuation is influenced by the opportunity to suckle lambs and the type of stressor. • Stressors that pose an immediate threat to the offspring evoke greater stress responses.

This study directly compared the dynamics of change in plasma corticosterone concentration with the dynamics of change in tissue corticosterone concentration in laying hens. In concert, we measured the rate of gluconeogenesis, glycogenesis, and glycolysis in the liver, kidney, skeletal muscle, and heart. We evaluated these changes acutely, over 3 h in response to an adrenocorticotropic hormone (ACTH) injection, and chronically, over 24 h in response to food and water deprivation. In response to ACTH injection, there was a significant (P < 0.05) increase in plasma corticosterone concentration and a parallel significant increase in corticosterone concentration in the skeletal muscle, kidney, and heart. However, the change in corticosterone concentration in the liver did not parallel the plasma, at times it was greater than the plasma, and there was a second significant increase (P < 0.05) in corticosterone concentration in the liver after 180 min. Under these conditions, the rate of gluconeogenesis in the liver decreased and the rate of glycogenesis increased. In contrast, after 12 h and 24 h of food and water deprivation plasma corticosterone concentration was increased, and this was paralleled by increased corticosterone concentration in the liver, an increase in the rate of gluconeogenesis and a decrease in the rate of glycogenesis. After ACTH injection, glucose concentration in the liver was not significantly depleted but after 12 h or 24 h of food and water deprivation it was significantly depleted (P < 0.05). Plasma corticosterone concentration provided different insight into the effect of the stressor on hen physiology under acute and chronic conditions. Our data suggest that extending our evaluation of stress to the site of corticosterone action, that is, the target tissue, may enhance our ability to evaluate stress and the welfare of laying hens.

Stress disrupts the preovulatory luteinizing hormone (LH) surge in females, but the mechanisms are unknown. We tested the hypothesis that cortisol compromises the ability of estrogen to induce a preovulatory-like LH surge in ovariectomized ewes in both the breeding and nonbreeding season. Luteinizing hormone surges were induced in ovariectomized ewes by treatment with progesterone followed by a surge-inducing estradiol-17beta (E2) stimulus using a crossover design. The experiment was replicated in the breeding and nonbreeding seasons. Cortisol reduced the incidence of LH surges irrespective of season. Cortisol increased the latency from E2 stimulus to the onset of the surge in the breeding season only and suppressed the LH surge amplitude during both seasons (P

Testosterone and season influence mRNA expression for the opioid, enkephalin, in the preoptic area and hypothalamus of rams. Dynorphin is another opioid which has been shown to play a role in the control of reproductive function in females. We now report effects of season and testosterone on the expression of prodynorphin mRNA in the hypothalamus of the ram. Castrated adult Romney Marsh rams (5/group) received vehicle or testosterone propionate (i.m.) during either the 'breeding' season or 'non-breeding' season. Prodynorphin mRNA expression was quantified in the hypothalami by in situ hybridisation. Testosterone treatment increased prodynorphin mRNA expression in the supraoptic nucleus and the bed nucleus of the stria terminalis in the breeding season but not during the non-breeding season. Prodynorphin mRNA expression was also higher in the breeding season than in the non-breeding season in the caudal preoptic area, paraventricular nucleus and accessory supraoptic nucleus, irrespective of treatment. No effects of treatment were observed in any other regions of the hypothalamus. We conclude that testosterone and season regulate prodynorphin mRNA expression in a region-specific manner, which may influence seasonal changes in reproductive function.

It is generally agreed that stress can impair reproduction. Furthermore, it is often thought that cortisol, which is secreted during stress as a result of activation of the hypothalamo-pituitary adrenal axis, is associated with this stress-induced impairment of reproduction. It has been hypothesized that reproduction in females is particularly susceptible to disruption by acute stress during the series of endocrine events that induce estrus and ovulation. Nevertheless, we found no support for this conjecture when we subjected female pigs to repeated acute stress or repeated acute elevation of cortisol during the period leading up to estrus and ovulation. Conversely, studies have demonstrated that prolonged stress and sustained elevation of cortisol can disrupt reproductive processes in female pigs. Nevertheless, in each study that demonstrated this effect, there were some animals subjected to the prolonged stressor or the sustained elevation of cortisol in which the reproductive parameters that were measured were not affected by the treatment. We propose that reproduction in female pigs is resistant to the effects of acute or repeated acute stress or acute or repeated acute elevation of cortisol even if these occur during the series of endocrine events that induce estrus and ovulation. Furthermore, while reproductive processes in some individuals are compromised, reproduction in a proportion of female pigs appears to be resistant to the effects of prolonged stress or sustained elevation of cortisol.