Department of Animal Sciences, University of Florida, Gainesville 32611.
Department of Animal Sciences, University of Puerto Rico, Mayagüez Campus, Puerto Rico 00682.
J Dairy Sci. 2020 May;103(5):4822-4837. doi: 10.3168/jds.2019-17926. Epub 2020 Feb 26.
Prenatal heat stress during late gestation exerts long-term effects on growth and productivity of the dairy calf. Further, direct exposure to heat stress during the preweaning period impairs calf thermoregulation and performance. We examined the effects of heat stress abatement during the prenatal period, postnatal period, or both on calf performance. We hypothesized that calves exposed to pre- and postnatal heat stress abatement would perform most optimally in terms of thermoregulation, growth, and health responses when compared with calves that are heat-stressed at any time in the pre- or postnatal periods. Holstein calves born to heat-stressed (HT) or cooled (CL) dams during late gestation (44 ± 5 d; prenatal HT or CL) were exposed to heat stress or cooling postnatally for 56 d (postnatal HT or CL), resulting in 4 treatments: HT-HT, HT-CL, CL-HT, and CL-CL; n = 12/treatment. Calves were administered 4 L of pooled colostrum and after 2 d of age allotted 10 L/d milk replacer and up to 3 kg/d concentrate in automatic feeder group pens (n = 6/pen). Postnatal cooling was achieved by 2 fans (average wind speed 2 m/s). Thermoregulatory responses (respiration rate and heart rate; rectal, body, and skin temperature), feed intake, growth parameters including average daily gain and medication events were recorded, and blood samples were collected weekly. Thermoregulatory responses were lower in postnatal CL calves compared with postnatal HT. In the afternoon, HT-HT calves had the highest respiration rate and rectal temperature, HT-CL calves had the lowest respiration rate, and CL-HT calves had the lowest heart rate compared with the other treatment groups. Prenatal CL calves weighed more at birth and weaning with a tendency for greater average daily gain compared with prenatal HT calves, whereas postnatal CL calves had increased milk replacer and concentrate intake and a tendency for reduced fever, infection, and total medication events relative to postnatal HT. Prenatal HT calves were esophageal tube fed more often than prenatal CL. Blood hematocrit and 24-h serum IgG concentration were greater in prenatal CL calves relative to prenatal HT. Prenatal heat stress abatement improves weight gain, hematocrit, and immunoglobulin transfer, whereas postnatal heat stress abatement modulates thermoregulatory responses, feed intake, and calf health. This study is the first to characterize the combined effects of pre- and postnatal heat stress or active cooling on the dairy calf.
孕期后期的产前热应激对奶牛犊牛的生长和生产性能产生长期影响。此外，在断奶前暴露于热应激会损害犊牛的体温调节和性能。我们研究了在孕期和产后期间减轻热应激对犊牛性能的影响。我们假设，与在孕期或产后任何时间受到热应激的犊牛相比，暴露于产前和产后热应激缓解的犊牛在体温调节、生长和健康反应方面表现最佳。在孕期后期（44±5d；产前 HT 或 CL），处于热应激（HT）或冷却（CL）状态的荷斯坦奶牛分娩的犊牛在产后 56d 内受到热应激或冷却（产后 HT 或 CL），导致 4 种处理：HT-HT、HT-CL、CL-HT 和 CL-CL；n=12/处理。犊牛接受 4L 混合初乳，2d 龄后，每天分配 10L 代乳粉和最多 3kg/d 浓缩饲料在自动饲喂组栏（n=6/栏）。产后冷却通过 2 个风扇（平均风速 2m/s）实现。记录体温调节反应（呼吸率和心率；直肠、体温和皮肤温度）、采食量、生长参数（包括平均日增重和用药事件），并每周采集血液样本。与产后 HT 相比，产后 CL 犊牛的体温调节反应（呼吸率和直肠温度）较低。在下午，HT-HT 犊牛的呼吸率和直肠温度最高，HT-CL 犊牛的呼吸率最低，CL-HT 犊牛的心率最低。与其他处理组相比。与产前 HT 犊牛相比，产前 CL 犊牛出生和断奶时体重较重，平均日增重有增加的趋势，而产后 CL 犊牛增加了代乳粉和浓缩饲料的摄入量，发烧、感染和总用药事件的发生率有降低的趋势。与产前 CL 相比，产前 HT 犊牛更频繁地经食管管饲。与产前 HT 相比，产前 CL 犊牛的血液红细胞压积和 24h 血清 IgG 浓度更高。孕期热应激缓解可提高体重增加、红细胞压积和免疫球蛋白转移，而产后热应激缓解可调节体温调节反应、采食量和犊牛健康。本研究首次描述了产前和产后热应激或主动冷却对奶牛犊牛的综合影响。
