Evaluation of heat stress abatement for pre-weaned dairy calves is a rare endeavor. We aimed to assess the impacts of cooling the environment of pre-weaned calves through ceiling fans on their performance after weaning and during their first lactation. We randomly assigned female Holstein calves to one of two treatment at birth (day 0): individual frame-wire hutches in a non-cooled barn ("SH", n = 125) and individual frame-wire hutches in a barn equipped with ceiling fans ("SHF", n = 101). Calves were housed under the same barn, with treatments applied in three alternating sections. Ceiling fans (2.1 m in diameter) were positioned 4.1 m from the ground and 7.6 m apart (center-to-center). Shade cloths were used to separate the sections designated for the SH and SHF treatments. Post-weaning, heifers were commingled. We recorded body weight (BW) and average daily gain (ADG) at weaning, 5, 7, and 10 mo of age. Pregnancy to first artificial insemination (P/1AI), hazard of pregnancy, and the hazard of commencing the first lactation are reported. Body weight at first calving, P/1AI, hazard of pregnancy, and milk yield in the first lactation are reported. No differences in BW (5 mo: SH = 162.9 ± 1.6 kg vs. SHF = 162.3 ± 1.6 kg; 7 mo: SH = 200.8 ± 2.2 kg vs. SHF = 201.1 ± 2.3 kg; 10 mo: SH = 300.5 ± 2.6 kg vs. SHF = 300.0 ± 2.8 kg) and ADG (SH = 0.94 ± 0.02 kg/d, SHF = 0.94 ± 0.02 kg/d) from 5 to 10 mo of age were detected. Treatment did not affect P/1AI (SH = 53.5 %, SHF = 45.9 %) and hazard of pregnancy [SH = referent, SHF – adjusted hazard ratio (AHR) = 0.87 (95 % CI = 0.65, 1.18)], but heifers in the SHF treatment were less likely to initiate the first lactation (76.2 % vs. 86.4 %). Body weight at calving (SH = 612.4 ± 5.3 kg, SHF = 618.2 ± 5.9 kg) and milk yield (SH = 39.0 ± 0.48 kg/d, SHF = 38.3 ± 0.57 kg/d) were not different, but the SHF treatment resulted in lower P/1AI (38.4 % vs. 51.4 %) and hazard of pregnancy (AHR = 0.68, 95 % CI = 0.49, 0.93) and fewer cows starting their second lactation (57.4 % vs. 72.8 %). In our experiment, providing cooling through ceiling fans during the pre-weaning phase had a negative impact on the reproductive performance of Holstein cows during their first lactation.

中文翻译：

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断奶前阶段降温对小母牛生长和繁殖性能以及奶牛健康、繁殖和生产性能影响的随机试验


对断奶前奶牛犊热应激缓解的评估是一项罕见的尝试。我们的目的是评估通过吊扇冷却断奶前犊牛的环境对其断奶后和第一次哺乳期间的表现的影响。我们将雌性荷斯坦犊牛在出生时（第 0 天）随机分配到两种治疗方法之一：非冷却谷仓中的单独框架钢丝笼（“SH”，n = 125）和配有天花板的谷仓中的单独框架钢丝笼粉丝（“SHF”，n = 101）。小牛被安置在同一个谷仓下，并在三个交替的部分进行治疗。吊扇（直径 2.1 m）距离地面 4.1 m，间距 7.6 m（中心到中心）。遮光布用于分隔指定用于 SH 和 SHF 处理的部分。断奶后，小母牛进行混种。我们记录断奶时、5月龄、7月龄和10月龄时的体重 (BW) 和平均日增重 (ADG)。报告了从怀孕到第一次人工授精 (P/1AI)、怀孕的风险以及开始第一次哺乳的风险。报告第一次产犊时的体重、P/1AI、妊娠风险和第一次哺乳期的产奶量。体重无差异（5 个月：SH = 162.9 ± 1.6 kg 与 SHF = 162.3 ± 1.6 kg；7 个月：SH = 200.8 ± 2.2 kg 与 SHF = 201.1 ± 2.3 kg；10 个月：SH = 300.5 ± 2.6 kg检测到 5 至 10 个月龄的日龄与 SHF = 300.0 ± 2.8 kg）和日增重（SH = 0.94 ± 0.02 kg/d，SHF = 0.94 ± 0.02 kg/d）。治疗不影响 P/1AI (SH = 53.5 %, SHF = 45.9 %) 和妊娠风险 [SH = 参考对象，SHF – 调整风险比 (AHR) = 0.87 (95 % CI = 0.65, 1.18)]，但小母牛接受 SHF 治疗的女性开始第一次哺乳的可能性较小（76.2% vs. 86.4%）。产犊时体重（SH = 612.4 ± 5.3 kg，SHF = 618.2 ± 5.9 kg）和产奶量（SH = 39。0 ± 0.48 kg/d，SHF = 38.3 ± 0.57 kg/d）没有差异，但 SHF 治疗导致较低的 P/1AI（38.4 % vs. 51.4 %）和妊娠风险（AHR = 0.68，95 % CI） = 0.49, 0.93），开始第二次泌乳的奶牛数量减少（57.4 % vs. 72.8 %）。在我们的实验中，在断奶前阶段通过吊扇提供冷却对荷斯坦奶牛在第一次泌乳期间的繁殖性能产生了负面影响。