Department of Animal Science, Iowa State University, Ames 50011; Department of Animal Production, The University of Jordan, Amman, Jordan 11942.
Department of Animal Science, Iowa State University, Ames 50011.
J Dairy Sci. 2020 Jun;103(6):5550-5560. doi: 10.3168/jds.2019-17543. Epub 2020 Mar 27.
The efficacy of an electric heat blanket (EHB) has previously been confirmed as an alternative method to evaluate heat stress (HS). However, a pair-feeding design has not been used with the EHB model. Therefore, study objectives were to determine the contribution of the nutritional plane to altered metabolism and productivity during EHB-induced HS. Multiparous Holstein cows (n = 18; 140 ± 10 d in milk) were subjected to 2 experimental periods (P); during P1 (4 d), cows were in thermoneutral conditions with ad libitum feed intake. During P2 (4 d), cows were assigned to 1 of 2 treatments: (1) thermoneutral conditions and pair-fed (PF; n = 8) or (2) EHB-induced HS with ad libitum feed intake (n = 10). Overall, the EHB increased rectal temperature, vaginal temperature, skin temperature, and respiration rate (1.4°C, 1.3°C, 0.8°C, and 42 breaths/min, respectively) relative to PF cows. The EHB reduced dry matter intake (DMI; 47%) and, by design, PF cows had a similar pattern and extent of decreased DMI. Milk yield decreased in EHB and PF cows by 27.3% (12.1 kg) and 13.4% (5.4 kg), respectively, indicating that reduced DMI accounted for only ∼50% of decreased milk synthesis. Milk fat content tended to increase (19%) in the EHB group, whereas in the PF cows it remained similar relative to P1. During P2, milk protein and lactose contents tended to decrease or decreased (1.3 and 2.2%, respectively) in both EHB and PF groups. Milk urea nitrogen remained unchanged in PF controls but increased (34.2%) in EHB cows relative to P1. The EHB decreased blood partial pressure of CO, total CO, HCO, and base excess levels (17, 16, 17, and 81%, respectively) compared with those in PF cows. During P2, the EHB and PF cows had similar decreases (4%) in plasma glucose content, but no differences in circulating insulin were detected. However, a group by day interaction was detected for plasma nonesterified fatty acids; levels progressively increased in PF controls but remained unaltered in the EHB cows. Blood urea nitrogen increased in the EHB cows (61%) compared with the PF controls. In summary, utilizing the EHB model indicated that reduced nutrient intake explains only about 50% of the decrease in milk yield during HS, and the postabsorptive changes in nutrient partitioning are similar to those obtained in climate-controlled chamber studies. Consequently, the EHB is a reasonable and economically feasible model to study environmental physiology of dairy cows.
电加热毯（EHB）的功效已被证实是评估热应激（HS）的替代方法。然而，EHB 模型尚未采用配对喂养设计。因此，本研究的目的是确定营养水平对 EHB 诱导的 HS 期间代谢和生产力改变的贡献。产奶牛（n = 18；泌乳 140 ± 10 天）进行了 2 个实验期（P）；在 P1（4 天）期间，奶牛处于热中性条件下，可自由采食。在 P2（4 天）期间，奶牛被分配到以下 2 种处理之一：（1）热中性条件和配对喂养（PF；n = 8）或（2）EHB 诱导的 HS 且自由采食（n = 10）。总的来说，EHB 使直肠温度、阴道温度、皮肤温度和呼吸频率分别升高了 1.4°C、1.3°C、0.8°C 和 42 次/分钟，高于 PF 奶牛。EHB 降低了干物质摄入量（DMI；47%），并且通过设计，PF 奶牛的 DMI 也呈现出相似的减少模式和程度。EHB 和 PF 奶牛的产奶量分别减少了 27.3%（12.1 公斤）和 13.4%（5.4 公斤），表明 DMI 的减少仅占牛奶合成减少的约 50%。EHB 组的牛奶脂肪含量趋于增加（19%），而 PF 奶牛的牛奶脂肪含量与 P1 相比保持不变。在 P2 期间，EHB 和 PF 组的牛奶蛋白和乳糖含量均趋于降低或降低（分别为 1.3%和 2.2%）。PF 对照组的牛奶尿素氮保持不变，但 EHB 奶牛的牛奶尿素氮与 P1 相比增加了 34.2%。EHB 降低了血液二氧化碳分压、总二氧化碳、HCO 和碱剩余水平（分别为 17%、16%、17%和 81%），与 PF 奶牛相比。在 P2 期间，EHB 和 PF 奶牛的血浆葡萄糖含量均降低（4%），但未检测到循环胰岛素的差异。然而，在血浆非酯化脂肪酸方面检测到了组间天交互作用；PF 对照组的水平逐渐升高，但 EHB 奶牛的水平保持不变。EHB 奶牛的血尿素氮增加（61%），高于 PF 对照组。总之，利用 EHB 模型表明，在 HS 期间，营养摄入减少仅解释了产奶量减少的约 50%，并且吸收后营养分配的变化与在气候控制室内研究中获得的变化相似。因此，EHB 是研究奶牛环境生理学的合理且经济可行的模型。
