Department of Animal Science, University of California, Davis, Davis, CA 95616.
Department of Animal Science, University of California, Davis, Davis, CA 95616.
J Dairy Sci. 2023 Dec;106(12):8942-8952. doi: 10.3168/jds.2023-23396. Epub 2023 Sep 9.
Heat stress (HS) during the dry period can affect animal welfare, health, dry matter intake (DMI), and milk production in the subsequent lactation, which will negatively affect the profitability of dairy farms. In this study, the objective was to model the changes in DMI in pregnant nonlactating heat-stressed dairy cows with or without access to evaporative cooling systems. A database was built, composed of individual DMI records from 244 pregnant nonlactating dairy cows from an average -29.3 d (range: -42 to -21 d; SD: ±7.54 d) to -1 d relative to calving (DRC) and housed in environmental conditions in which temperature-humidity index (THI) ranged from 58.4 to 83.3, with or without access to evaporative cooling systems. Generalized additive mixed-effects models were used to describe the relationships of DMI with HS and DRC. Changes in DMI with the increase in THI and the progression of pregnancy in cows with or without evaporative cooling systems were estimated using differential equations. On average, cows housed in barns without evaporative cooling systems had a reduction in DMI of 1.30 kg/d and increased rectal temperature in 0.22°C in relation to those housed in barns with evaporative cooling systems. Dry matter intake decreased as THI increased, but the reduction was greater for noncooled cows as THI values increased. In addition, regardless of the THI, DMI started to decrease at -14 DRC for cooled cows, whereas for noncooled cows it already started at -30 DRC, relative to the previous days evaluated. The intensity of the reduction was lesser for cows that had access to evaporative cooling systems or were in the dry period in May to June as compared with those that were in the dry period in July to August or September to October. The models generated in this study, which include environmental variables, should lead to more accurate predictions of DMI during HS that can be used to formulate diets to meet the needs of the late pregnant cow because it is possible to predict changes in DMI as the heat load and DRC change. Such models are also expected to help dairy nutritionists to decide when and how to apply the dietary strategies available to attenuate the reductions in DMI with the intensity of HS and progression of pregnancy.
热应激（HS）会影响动物福利、健康、干物质采食量（DMI）和随后泌乳期的产奶量，从而降低奶牛场的盈利能力。本研究旨在建立模型，预测有或没有蒸发式冷却系统的热应激干奶牛的 DMI 变化。该数据库由 244 头处于干奶期的未泌乳奶牛的个体 DMI 记录组成，这些奶牛的 DRC 时间为平均-29.3 天（范围：-42 至-21 天；SD：±7.54 天）至-1 天，饲养环境的温度-湿度指数（THI）范围为 58.4 至 83.3，有或没有蒸发式冷却系统。使用广义加性混合效应模型来描述 DMI 与 HS 和 DRC 的关系。使用微分方程来估计有无蒸发式冷却系统的奶牛，THI 增加和妊娠进展时 DMI 的变化。平均而言，与有蒸发式冷却系统的牛舍相比，没有蒸发式冷却系统的牛舍中的奶牛的 DMI 减少了 1.30 公斤/天，直肠温度升高了 0.22°C。随着 THI 的增加，DMI 减少，但对于没有冷却的奶牛，随着 THI 值的增加，减少量更大。此外，无论 THI 如何，对于冷却的奶牛，DMI 在 DRC-14 天开始减少，而对于未冷却的奶牛，DMI 已经在 DRC-30 天开始减少，与前几天相比。与 7 月至 8 月或 9 月至 10 月处于干奶期的奶牛相比，5 月至 6 月处于干奶期的奶牛或有蒸发式冷却系统的奶牛，DMI 减少的强度更小。本研究中生成的模型包括环境变量，应能更准确地预测 HS 期间的 DMI，可用于制定满足后期妊娠奶牛需求的日粮，因为可以预测随着热负荷和 DRC 的变化，DMI 的变化。这些模型还可以帮助奶牛营养师决定何时以及如何应用现有的饮食策略来减轻 DMI 随着 HS 强度和妊娠进展的减少。
