Department of Animal Sciences, Purdue University, West Lafayette, IN 47907, USA.
USDA-ARS, Livestock Behavior Research Unit, West Lafayette, IN 47907, USA.
J Anim Sci. 2024 Jan 3;102. doi: 10.1093/jas/skae171.
The study objective was to investigate the effect of repeated hypothalamic-pituitary-adrenal (HPA) axis stimulation using synthetic adrenocorticotropic hormone (ACTH) intramuscular injections on hair cortisol concentration, growth, and behavior in preweaned dairy calves. Twenty-seven Holstein calves were assigned to nine triads (based on sex and birth order) and randomly assigned to 1 of 3 treatments: 1) control (CON; 2 mL saline weekly); 2) moderate (MOD; alternating Cosyntropin [2 mcg/kg body weight (BW)] and saline weekly); or 3) frequent (FREQ; Cosyntropin [2 mcg/kg BW] weekly). Calves received their first injection on study day 0 (7 ± 1 d of age). Hair was collected from the tail switch between days -5 and -3 (baseline), 21, and 49 and analyzed for cortisol concentration. To verify the endogenous cortisol release by Cosyntropin during the treatment period, saliva was collected on days 0, 14, 28, and 42 before injection and every 15 min for 2 h after injection for analysis of salivary cortisol concentration. Calves were fitted with accelerometers to continuously monitor lying time, number of lying bouts, and lying bout duration throughout the study. Growth measures (BW, hip height, hip width) were recorded weekly. Data were analyzed using repeated measures ANOVA (SAS, Version 9.4), and models included the fixed effects of treatment, time (min or study day), and interaction between treatment and time. Temperature humidity index was included as a continuous covariate in all models. We observed a treatment × min interaction (P < 0.0001), whereby salivary cortisol concentration was lower in CON calves compared to MOD and FREQ calves 15 to 120 min postinjection. While hair cortisol concentration was not influenced by treatment, concentration decreased from day 21 (1.28 ± 0.03 ng/mL) to 49 (0.93 ± 0.03 ng/mL). Average BW was similar across treatments (CON [59.4 ± 1.09 kg], MOD [58.6 ± 0.98 kg], and FREQ [57.6 ± 0.96 kg]; P = 0.50). There was no evidence to suggest a difference in average daily lying time (CON [18.5 ± 0.23 h/d], MOD [18.6 ± 0.23 h/d], and FREQ [18.5 ± 0.23 h/d]; P = 0.99). These results suggest that repeated HPA axis stimulation through Cosyntropin administration increased salivary cortisol concentration, but did not influence hair cortisol concentration, growth, or behavior in preweaned dairy calves.
本研究旨在探究使用合成促肾上腺皮质激素（ACTH）肌肉注射对预断奶奶牛小牛下丘脑-垂体-肾上腺（HPA）轴的重复刺激对毛发皮质醇浓度、生长和行为的影响。27 头荷斯坦小牛根据性别和出生顺序分为 9 组（triad），并随机分为 3 种处理之一：1）对照（CON；每周 2 mL 生理盐水）；2）中度（MOD；交替使用促皮质素（2 mcg/kg 体重（BW））和生理盐水每周）；或 3）频繁（FREQ；每周促皮质素[2 mcg/kg BW]）。小牛在研究第 0 天（7 ± 1 日龄）接受第一次注射。在-5 天至-3 天（基线）、21 天和 49 天之间从尾端采集毛发，并分析皮质醇浓度。为了验证促皮质素在治疗期间对内源性皮质醇释放的作用，在注射前的第 0、14、28 和 42 天以及注射后每 15 分钟收集唾液，分析唾液皮质醇浓度。使用加速度计连续监测小牛的躺卧时间、躺卧次数和躺卧持续时间。每周记录体重、臀部高度和臀部宽度等生长指标。使用重复测量方差分析（SAS，版本 9.4）对数据进行分析，模型包括处理、时间（分钟或研究日）和处理与时间的交互作用的固定效应。所有模型均包含温度湿度指数作为连续协变量。我们观察到处理×分钟的交互作用（P<0.0001），即在注射后 15 至 120 分钟，CON 小牛的唾液皮质醇浓度低于 MOD 和 FREQ 小牛。虽然毛发皮质醇浓度不受处理影响，但从第 21 天（1.28±0.03ng/mL）到第 49 天（0.93±0.03ng/mL）下降。各处理组间平均体重无差异（CON[59.4±1.09kg]，MOD[58.6±0.98kg]，FREQ[57.6±0.96kg]；P=0.50）。没有证据表明平均每日躺卧时间存在差异（CON[18.5±0.23h/d]，MOD[18.6±0.23h/d]，FREQ[18.5±0.23h/d]；P=0.99）。这些结果表明，通过促皮质素给药对 HPA 轴的重复刺激增加了唾液皮质醇浓度，但对预断奶奶牛小牛的毛发皮质醇浓度、生长和行为没有影响。
