Mahjoubi E, Yazdi M Hossein, Aghaziarati N, Noori G R, Afsarian O, Baumgard L H
J Anim Sci. 2015 Apr;93(4):1632-40. doi: 10.2527/jas.2014-8641.
The extent to which reduced feed intake contributes to decreased growth during heat stress (HS) in the ovine model is not clear. To evaluate the impact of decreased DMI on performance, we conducted an experiment on growing lambs experiencing a cyclical but extensive heat load. Sixteen intact male Afshari lambs (40.1 ± 1.9 kg) were used in a completely randomized design in 2 periods. In period 1, all 16 lambs were housed in thermal neutral (TN) conditions (22.2 ± 3.1°C and a temperature-humidity index [THI] of 67.9 ± 3.2) and fed at libitum for 8 d. In period 2 (P2), which lasted 9 d, 8 lambs were subjected to a cyclical HS condition (33.0 to 45.0°C and a THI of more than 80 at least for 24 h/d and more than 90 for 8 h/d). The other 8 lambs were maintained in TN conditions but pair-fed (pair-fed thermal neutral [PFTN]) to the HS lambs. During each period, DMI and water intake were measured daily. Respiration rate, rectal temperature, and skin temperature at the shoulder, rump, and front and rear leg were recorded at 0700 and 1400 h daily. Dry matte intake declined (17.5%; P < 0.01) in HS lambs and, by design, the temporal pattern and magnitude of reduced feed intake was similar in the PFTN controls. Water intake increased (19%; P < 0.05) during P2 in HS but not in the PFTN controls. Heat stress increased the 0700 and 1400 h skin temperature at the shoulder (5 and 9.2%), rump (6.2 and 10.3%), rear (6 and 9.2%), and front leg (6.5 and 9.8%) and respiratory rates (84 and 163% [P < 0.01]at 0700 and 1400 h, respectfully), but only the 1400 h rectal temperature was increased (P < 0.01; 0.65°C) in HS lambs. Neither environment nor period affected blood urea nitrogen and glucose concentrations. However, circulating NEFA and insulin were increased and declined (P < 0.01) in PFTN lambs, respectively, but neither variable was altered in the HS lambs. Growth was reduced in P2 for lambs in both treatments, but despite being on a similar reduced plane of nutrition, the HS lambs' ADG was more than 2-fold greater than the PFTN controls. These results indicate that HS markedly alters the energetics of weight gain during growth and that the effects of HS are dependent on the severity of the heat load.
在绵羊模型中，采食量减少在热应激（HS）期间对生长下降的影响程度尚不清楚。为了评估干物质采食量（DMI）下降对生产性能的影响，我们对经历周期性但强烈热负荷的生长羔羊进行了一项实验。16只未阉割的雄性阿夫沙里羔羊（40.1±1.9千克）被用于完全随机设计的两个阶段实验。在第1阶段，所有16只羔羊饲养在热中性（TN）条件下（22.2±3.1°C，温度湿度指数[THI]为67.9±3.2），自由采食8天。在持续9天的第2阶段（P2），8只羔羊经历周期性热应激条件（33.0至45.0°C，THI至少24小时/天超过80，8小时/天超过90）。另外8只羔羊保持在TN条件下，但与热应激羔羊进行配对饲喂（配对饲喂热中性[PFTN]）。在每个阶段，每天测量DMI和饮水量。每天0700和1400时记录呼吸频率、直肠温度以及肩部、臀部、前后腿的皮肤温度。热应激羔羊的干物质采食量下降（17.5%；P<0.01），按照设计，PFTN对照组采食量减少的时间模式和幅度与之相似。热应激组在P2期间饮水量增加（19%；P<0.05），而PFTN对照组未增加。热应激使0700和1400时肩部（5%和9.2%）、臀部（6.2%和10.3%）、后腿（6%和9.2%）和前腿（6.5%和9.8%）的皮肤温度以及呼吸频率升高（0700和1400时分别为84%和163%[P<0.01]），但热应激羔羊仅1400时的直肠温度升高（P<0.01；0.65°C）。环境和阶段均未影响血液尿素氮和葡萄糖浓度。然而，PFTN羔羊的循环非酯化脂肪酸（NEFA）增加，胰岛素下降（P<0.01），但热应激羔羊这两个变量均未改变。两种处理的羔羊在P2阶段生长均减缓，但尽管营养水平下降程度相似，热应激羔羊的平均日增重（ADG）比PFTN对照组高出2倍多。这些结果表明，热应激显著改变生长期间体重增加的能量代谢，且热应激的影响取决于热负荷的严重程度。
