Vitali A, Felici A, Esposito S, Bernabucci U, Bertocchi L, Maresca C, Nardone A, Lacetera N
Dipartimento di Scienze e Tecnologie per l'Agricoltura, le Foreste, la Natura e l'Energia, Università della Tuscia, 01100 Viterbo, Italy.
Istituto Zooprofilattico Sperimentale dell'Umbria e delle Marche, 06126 Perugia, Italy.
J Dairy Sci. 2015 Jul;98(7):4572-9. doi: 10.3168/jds.2015-9331. Epub 2015 May 7.
This study investigated the mortality of dairy cows during heat waves. Mortality data (46,610 cases) referred to dairy cows older than 24mo that died on a farm from all causes from May 1 to September 30 during a 6-yr period (2002-2007). Weather data were obtained from 12 weather stations located in different areas of Italy. Heat waves were defined for each weather station as a period of at least 3 consecutive days, from May 1 to September 30 (2002-2007), when the daily maximum temperature exceeded the 90th percentile of the reference distribution (1971-2000). Summer days were classified as days in heat wave (HW) or not in heat wave (nHW). Days in HW were numbered to evaluate the relationship between mortality and length of the wave. Finally, the first 3 nHW days after the end of a heat wave were also considered to account for potential prolonged effects. The mortality risk was evaluated using a case-crossover design. A conditional logistic regression model was used to calculate odds ratio and 95% confidence interval for mortality recorded in HW compared with that recorded in nHW days pooled and stratified by duration of exposure, age of cows, and month of occurrence. Dairy cows mortality was greater during HW compared with nHW days. Furthermore, compared with nHW days, the risk of mortality continued to be higher during the 3 d after the end of HW. Mortality increased with the length of the HW. Considering deaths stratified by age, cows up to 28mo were not affected by HW, whereas all the other age categories of older cows (29-60, 61-96, and >96mo) showed a greater mortality when exposed to HW. The risk of death during HW was higher in early summer months. In particular, the highest risk of mortality was observed during June HW. Present results strongly support the implementation of adaptation strategies which may limit heat stress-related impairment of animal welfare and economic losses in dairy cow farm during HW.
本研究调查了热浪期间奶牛的死亡率。死亡数据（46610例）涉及年龄超过24个月的奶牛，这些奶牛在6年期间（2002 - 2007年）的5月1日至9月30日期间因各种原因死于农场。气象数据来自位于意大利不同地区的12个气象站。对于每个气象站，热浪被定义为从5月1日至9月30日（2002 - 2007年）期间至少连续3天，当日最高温度超过参考分布（1971 - 2000年）的第90百分位数的时段。夏季天数被分类为处于热浪（HW）或不处于热浪（nHW）的日子。对处于HW的日子进行编号，以评估死亡率与热浪持续时间之间的关系。最后，还考虑了热浪结束后的前3个nHW日子，以考虑潜在的长期影响。使用病例交叉设计评估死亡风险。采用条件逻辑回归模型计算与按暴露持续时间、奶牛年龄和发生月份汇总及分层的nHW日子相比，HW期间记录的死亡率的比值比和95%置信区间。与nHW日子相比，HW期间奶牛死亡率更高。此外，与nHW日子相比，HW结束后的3天内死亡风险仍然更高。死亡率随HW持续时间增加。按年龄分层考虑死亡情况，28个月及以下的奶牛不受HW影响，而其他所有年龄较大的奶牛类别（29 - 60、61 - 96和>96个月）在暴露于HW时死亡率更高。HW期间初夏月份的死亡风险更高。特别是，6月的HW期间观察到最高的死亡风险。目前的结果有力地支持了实施适应策略，这可能会限制热浪期间奶牛场与热应激相关的动物福利损害和经济损失。
