Abstract：
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.
摘要：
对断奶前乳牛的热应激缓解进行评估是一项罕见的工作。我们旨在评估通过吊扇冷却断奶前小牛的环境对断奶后和首次哺乳期间的表现的影响。我们在出生时（第0天）将雌性荷斯坦小牛随机分配到两种治疗中的一种：在未冷却的谷仓中单独使用框架金属丝（“SH”，n=125）和配有吊扇的谷仓中的单个框架金属丝箱（“SHF”，n=101)。小牛被安置在同一个谷仓下,在三个交替的部分应用治疗。吊扇（直径2.1m）位于距地面4.1m，相距7.6m（中心到中心）。使用遮光布来分离指定用于SH和SHF处理的切片。断奶后,小母牛混在一起。我们记录了断奶时的体重（BW）和平均日增重（ADG），5、7和10个月的年龄。妊娠至首次人工授精（P/1AI），怀孕的危险，并报告了开始第一次哺乳的危险。第一次产奶时的体重，P/1AI,怀孕的危险，报告了第一次泌乳时的产奶量。体重没有差异(5个月：SH=162.9±1.6千克与SHF=162.3±1.6kg;7mo:SH=200.8±2.2kgvs.SHF=201.1±2.3kg;10mo:SH=300.5±2.6kgvs.SHF=300.0±2.8kg)和ADG(SH=0.94±0.02kg/d,SHF=0.94±0.02kg/d），从5到10个月龄检测到。治疗不影响P/1AI（SH=53.5%，SHF=45.9%)和妊娠危险[SH=参考，SHF-调整后的危险比（AHR）=0.87（95％CI=0.65，1.18）]，但是在SHF治疗中的小母牛不太可能开始第一次泌乳(76.2%vs.86.4%）。分娩时的体重（SH=612.4±5.3kg，SHF=618.2±5.9kg）和产奶量（SH=39.0±0.48kg/d，SHF=38.3±0.57kg/d)没有差异，但SHF治疗导致P/1AI降低（38.4%vs.51.4%）和妊娠危险（AHR=0.68，95%CI=0.49，0.93），开始第二次泌乳的奶牛较少（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哺乳期间的繁殖性能有负面影响。
