最近的证据表明,热应激对小牛生长性能的损失与营养物质的转移有关,以控制肠炎和全身性炎症。在这项研究中,我们研究了热应激对炎症标志物的影响,饲料利用效率,和奶牛的生长。我们假设地塞米松,以其免疫抑制和抗炎特性而闻名,将减少炎症并恢复暴露于热应激下的小牛的生长。32只荷斯坦公牛(体重(BW)68.5±1.37kg;年龄3.5±0.5周龄;平均值±SD)在恒定的环境温度下被安置在气候受控房间的单个围栏中,并在开始治疗前5天调整设施。在2×2阶乘排列的环境中,将小牛随机分配到4种治疗方法之一(n=8/治疗)(ENV,热中性或热应激)和干预(INT,生理盐水或地塞米松)持续5d,如下所示:1)热中性(恒定环境温度为20°C24h/d)和生理盐水的给药,2)热中性(恒定环境温度为20°C24h/d)和地塞米松的给药,3)循环热应力(40°C环境温度,从0800到1900小时/天)和生理盐水的施用,4)循环热应力(40°C环境温度,从0800到1900小时/天)和地塞米松的给药。地塞米松(0.05mg/kg体重),或生理盐水(1.2mL)在第1天和第3天肌内给药。治疗完成后,在第5天对小牛进行安乐死以获得空肠粘膜样品。商业牛奶替代品,起动器颗粒,提供了水,每天监测摄入量。每天3次监测直肠温度和呼吸频率。在第1、3和5天收集血样以测定血清促炎细胞因子浓度。收集空肠的切片并快速冷冻以确定促炎标记物的浓度。统计分析包括混合模型,ENV的固定效应,INT,随时间进行的连续测量(d,h,或两者),副本,以及小腿和错误的随机影响(SAS9.4版,SASInstituteInc.,凯里,NC)。在治疗分配之前立即收集的测量值作为协变量包括在模型中。ENV效应表明,热应激会增加直肠温度(38.72vs.39.21°C),呼吸频率(36vs.108次呼吸/分钟),和水的摄入量(3.2vs.6.6L/d)。处理不影响干物质摄入。ENV×INT相互作用表明,生理盐水的热应激使平均日增重(ADG)降低了35%,并使饲料利用效率降低了36%。但是使用地塞米松治疗热应激可恢复ADG和饲料利用效率,与基础水平相当。ENV×INT相互作用表明,生理盐水热应激使空肠白细胞介素(IL)-6浓度增加2倍,但是热应激的地塞米松治疗使空肠IL-6浓度恢复至基础水平。热应激-免疫促炎反应的生物能量成本介于ME的1.18和1.50Mcal之间。总的来说,地塞米松的给药降低了一种促炎标志物的空肠浓度,并恢复了与热应激相关的生长和饲料利用效率的降低.地塞米松的免疫调节和抗炎作用可能是稳态变化的一部分,该变化导致从维持功能转变为支持暴露于热应激的小牛的生长。
Recent evidence indicates that the heat stress loss on the growth performance of calves is associated with the diversion of nutrients to control enteritis and systemic inflammation. In this study, we investigated the impact of heat stress on markers of inflammation, feed use-efficiency, and growth of dairy calves. We hypothesized that dexamethasone, which is known for its immunosuppressive and anti-inflammatory properties, would reduce inflammation and restore the growth of calves exposed to heat stress. Thirty-two Holstein bull calves (body weight (BW) 68.5 ± 1.37 kg; age 3.5 ± 0.5-week-old; mean ± SD) were housed in individual pens in climate-controlled rooms at constant ambient temperature and allowed to adjust to facilities for 5 d before the start of treatments. Calves were randomly assigned to one of 4 treatments (n = 8/treatment) in a 2 × 2 factorial arrangement of environment (ENV, thermoneutral or heat stress) and intervention (INT, saline or dexamethasone) imposed for 5 d as follow: 1) thermoneutral (constant ambient temperature of 20°C 24 h/d) and administration of saline, 2) thermoneutral (constant ambient temperature of 20°C 24 h/d) and administration of dexamethasone, 3) cyclic heat stress (40°C ambient temperature, from 0800 to 1900 h/d) and administration of saline, 4) cyclic heat stress (40°C ambient temperature, from 0800 to 1900 h/d) and administration of dexamethasone. Dexamethasone (0.05 mg/kg BW), or saline (1.2 mL) was administered intramuscularly on d 1 and 3. Upon completion of treatments, calves were euthanized on d 5 to obtain jejunum mucosa samples. Commercial milk replacer, starter grain, and water were offered, and intake was monitored daily. Rectal temperature and respiratory rate were monitored 3 times daily. Blood samples were collected on d 1, 3, and 5 to determine serum pro-inflammatory cytokine concentrations. A section of the jejunum was collected and snap-frozen to determine the concentration of pro-inflammatory markers. Statistical analyses included a mixed model, fixed effects of ENV, INT, consecutive measurements taken over time (d, h, or both), replica, and random effects of calf and error (SAS version 9.4, SAS Institute Inc., Cary, NC). The measurements collected immediately before treatment allocation were included as covariates in the model. An ENV effect showed that heat stress increased rectal temperature (38.72 vs. 39.21°C), respiratory rate (36 vs. 108 breaths/min), and water intake (3.2 vs. 6.6 L/d). The treatments did not affect dry matter intake. An ENV × INT interaction showed that heat stress with saline decreased average daily gain (ADG) by 35% and tended to decrease feed use-efficiency by 36%, but the use of dexamethasone to treat heat stress restored ADG and feed use-efficiency comparable to their basal levels. An ENV × INT interaction revealed that heat stress with saline increased jejunal interleukin (IL)-6 concentration 2-fold, but dexamethasone treatment of heat stress restored jejunal IL-6 concentration to basal levels. The bioenergetic cost of the heat stress-immune pro-inflammatory response ranged between 1.18 and 1.50 Mcal of ME. Overall, the administration of dexamethasone reduced the jejunal concentration of a pro-inflammatory marker and restored the heat stress-associated reduction in growth and feed use-efficiency. The immunomodulation and anti-inflammatory effects of dexamethasone could be part of a homeorhetic change that results in a shift from maintenance functions to support growth on calves exposed to heat stress.