Melbourne School of Land and Environment, The University of Melbourne, Parkville, Victoria, Australia.
Domest Anim Endocrinol. 2010 Aug;39(2):137-46. doi: 10.1016/j.domaniend.2010.03.003. Epub 2010 Apr 27.
Metabolic rate and energy consumption increase through the activation of the hypothalamic-pituitary-adrenal axis when an animal is exposed to a stressor. Residual feed intake (RFI) as a measure of efficiency has been shown to be related to exogenous adrenocorticotropin hormone (ACTH)-stimulated cortisol concentrations, which is indicative of the relationship between an animal's response to stress and the efficiency with which the energy is used for growth and production. In this study, we tested the hypothesis that sheep with low post-ACTH serum cortisol concentration relative to the other sheep in the flock have lower RFI values and lower cortisol concentrations following insulin-induced hypoglycemia. Adrenocorticotropin hormone (2.0 microg/kg body weight)-stimulated cortisol concentrations were measured in 100 sheep. The extreme responders were selected (n = 12 high cortisol, n = 12 low cortisol), and feed efficiency and body composition parameters were measured. A second ACTH challenge and an insulin challenge were administered. More efficient sheep (more negative RFI value) were found to have lower (P < 0.05) cortisol concentrations following both an ACTH challenge and an insulin challenge. Low-cortisol sheep (low response to ACTH or insulin) were found to have a lower (P < 0.05) proportion of fat tissue in comparison to the high-cortisol animals. These data clearly indicate that an animal's response to exogenous ACTH or insulin-induced hypoglycemia as a stressor is related (P < 0.05) to efficiency of energy use when measured as RFI. These data have important implications in enabling identification of animals that are superior in terms of feed efficiency and for understanding the physiological mechanisms underlying efficiency of energy use.
当动物暴露于应激源时，下丘脑-垂体-肾上腺轴的激活会导致代谢率和能量消耗增加。残留采食量（RFI）作为效率的衡量标准已被证明与外源性促肾上腺皮质激素（ACTH）刺激的皮质醇浓度有关，这表明动物对压力的反应与能量用于生长和生产的效率之间存在关系。在这项研究中，我们检验了一个假设，即相对于群体中其他绵羊，ACTH 后血清皮质醇浓度较低的绵羊具有较低的 RFI 值，并且在胰岛素诱导的低血糖后皮质醇浓度较低。对 100 只绵羊进行了 2.0 微克/千克体重的 ACTH 刺激皮质醇浓度的测量。选择了极端反应者（n = 12 例高皮质醇，n = 12 例低皮质醇），并测量了饲料效率和身体成分参数。进行了第二次 ACTH 挑战和胰岛素挑战。发现效率更高的绵羊（RFI 值更负）在接受 ACTH 挑战和胰岛素挑战后皮质醇浓度较低（P < 0.05）。低皮质醇绵羊（对 ACTH 或胰岛素的反应较低）与高皮质醇动物相比，脂肪组织的比例较低（P < 0.05）。这些数据清楚地表明，动物对外源 ACTH 或胰岛素诱导的低血糖作为应激源的反应与作为 RFI 测量的能量利用效率相关（P < 0.05）。这些数据对于识别在饲料效率方面具有优势的动物以及理解能量利用效率的生理机制具有重要意义。
