Abbott Chelsea R, Saxton Arnold M, Rispoli Louisa A, Payton Rebecca R, Pohler Ky G, Schrick F Neal, Edwards J Lannett
Department of Animal Science, The University of Tennessee Institute of Agriculture and AgResearch, Knoxville, TN, USA.
Department of Animal Science, The University of Tennessee Institute of Agriculture and AgResearch, Knoxville, TN, USA.
J Therm Biol. 2018 Dec;78:247-256. doi: 10.1016/j.jtherbio.2018.10.003. Epub 2018 Oct 17.
Hyperthermia occurring 10-12 h after LH surge reduces quality of maturing oocyte, thereby reducing fertility. Objective was to examine consequences of an acute heat stress and the influence of certain hormones on the thermoregulatory responses of lactating cows during this critical period. Between the months of February through May, cows were transported to a facility and maintained at a temperature-humidity index (THI) of 65.9 ± 0.2 (thermoneutral) or exposed to changes in THI to simulate what may occur during an acute heat stress event (71-86 THI; heat stress); cows were rapidly cooled thereafter. Mixed model regressions with repeated measures were used to test respiration rates (RR) and rectal temperature (RT). Within 40 and 110 min of increasing THI, RR increased in a quadratic fashion (P < 0.001); RT increased by 0.04 ± 0.1 °C (P < 0.001) per unit THI. Changes in RR lagged THI and preceded rises in RT. Average THI 3-days before treatment (prior THI) influenced RR (P = 0.050) and RT (P < 0.001) changes. Increased RR was more noticeable in heat-stressed cows when prior THI was in the 40 s. Rectal temperature of heat-stressed cows was 0.8 ± 0.02 °C lower when prior THI was in the 40 s versus low 60 s. Levels of progesterone and luteinizing hormone before treatment were predictive of thermoregulatory response in heat-stressed cows. Rapid cooling decreased RR by 0.6 ± 0.1 bpm (P < 0.001) and RT by 0.02 ± 0.002 °C per min (P < 0.002). Speed and magnitude of thermoregulatory changes to an acute heat stress and after sudden cooling emphasizes importance of strategic cooling before ovulation. Efforts to do so when prior THI approaches levels expected to induce mild stress are especially important. Respiration rate is a useful indicator of the degree of hyperthermia a lactating cow is experiencing.
促黄体生成素高峰后10 - 12小时出现的体温过高会降低成熟卵母细胞的质量，从而降低生育能力。目的是研究急性热应激的后果以及某些激素对泌乳奶牛在此关键时期体温调节反应的影响。在2月至5月期间，将奶牛运至一个设施中，使其保持在温度 - 湿度指数（THI）为65.9±0.2（热中性）的环境中，或使其暴露于THI的变化中以模拟急性热应激事件期间可能发生的情况（71 - 86 THI；热应激）；此后迅速对奶牛进行降温。采用重复测量的混合模型回归来测试呼吸频率（RR）和直肠温度（RT）。在THI升高的40至110分钟内，RR呈二次方增加（P < 0.001）；每单位THI，RT升高0.04±0.1°C（P < 0.001）。RR的变化滞后于THI且先于RT升高。治疗前3天的平均THI（之前的THI）影响RR（P = 0.050）和RT（P < 0.001）的变化。当之前的THI在40多的时候，热应激奶牛的RR升高更为明显。当之前的THI在40多而不是60低的时候，热应激奶牛的直肠温度低0.8±0.02°C。治疗前孕酮和促黄体生成素的水平可预测热应激奶牛的体温调节反应。快速降温使RR每分钟降低0.6±0.1次/分钟（P < 0.001），RT每分钟降低0.02±0.002°C（P < 0.002）。对急性热应激和突然降温的体温调节变化的速度和幅度强调了排卵前进行策略性降温的重要性。当之前的THI接近预期会诱发轻度应激的水平时，这样做的努力尤为重要。呼吸频率是泌乳奶牛所经历的体温过高程度的一个有用指标。
