Heat-related mortality in dairy cattle A case crossover study

The relationship between mortality and stressful weather is not only a complex health social and environmental Issue but also becomes an economical problem when considering livestock Future-climate scenarios suggest that higher global mean temperatures could result in marked changes in the frequency of extreme temperatures The relationship between high temperature and mortality is well known in people living in urban areas but it has been poorly investigated in livestock such as dairy cows The aim of this study was to quantify the relationship between heat and mortality from all causes among dairy cows in Italy We studied 6697 adult (>24 months) dairy cows that died during the summer in the 5-year period 2002-2006 in three Italian districts (Brescia Cuneo Rome) which were selected because of the high livestock production and the availability of weather data for these geographical areas A case-crossover design was applied using the temperature-humidity index (THI) as exposure of interest Pooled odds ratio (OR) of mortality at high exposure values versus low exposure values was estimated An exposure over the THI cutoff increased the risk of mortality by 1 6 times with a 4% increase in mortality for each THI degree increase above the threshold We found no effect modification for age-class herd size or breed but a certain degree of geographical heterogeneity was identified The increased dairy cow mortality highlighted in this study should be considered when adopting animal welfare and farm management measures This phenomenon can be prevented by adopting appropriate interventions to mitigate environmental thermal challenges (C) 2010 Elsevier BV All rights reserved