The effect of heat waves on dairy cow mortality
Author(s)
Date Issued
2015
Type
article
Volume
98
Issue
98
Start Page
4572
End Page
4579
ISSN
220302
Journal
Abstract
This study investigated the mortality of dairy cows during heat waves. Mortality data (46,610 cases) referred to dairy cows older than 24 mo 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 28 mo were
not affected by HW, whereas all the other age categories of older cows (29–60, 61–96, and >96 mo) 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.
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Conference(s)
JOURNAL OF DAIRY SCIENCE