Seasonal pattern of mortality and relationships between mortality and temperature-humidity index in dairy cows

Abstract

The 2 studies described investigated seasonal variations of mortality and temperature-humidity index (THI)-mortality relationships in dairy cows. Mortality data were extracted from the Italian Bovine Spongiform Encephalopathy databases, which contain records on cows older than 24 mo that died on a farm from all causes (98% of total records), were slaughtered in an emergency state, or were sent for normal slaughter but were sick in the preslaughter inspection (2% of total records). Both studies evaluated mortality data during a 6-yr period (2002 to 2007). The seasonal pattern study was conducted throughout Italy and was based on 320,120 deaths. An association between season and deaths was found for all 6 yr. Summer and spring were the seasons with the highest and lowest frequency of deaths (15,773.3 +/- 2,861 and 11,619.3 +/- 792.3), respectively, and within summer months, the number of deaths in July and August (5,435 +/- 284 and 5,756 +/- 676.2, respectively) was higher than in June (4,839 +/- 344.8). The THI-mortality relationships study was carried out only for deaths (51,240) reported for the Lombardia and Emilia Romagna regions. For this study, the mortality databases were integrated with THI data, which were calculated by using data from 73 weather stations. Each farm where deaths were recorded was assigned the THI values (maximum and minimum) calculated at the closest weather station for each day the events (deaths) were reported. Analysis of data indicated that approximate THI values of 80 and 70 were the maximum and minimum THI, respectively, above which the number of deaths in dairy farms starts to increase. Maximum and minimum THI values of 87 and 77 were the upper critical THI above which the risk of death for dairy cows becomes maximum. This study defined quantitative relationships between mortality risk and THI in dairy cows and may help to provide emergency interventions and mitigation measures, which may ensure survival of dairy cows and reduce replacement costs associated with heat stress-related mortality.

Changes in the genetic level and the effects of age at first calving and milk production on survival during the first lactation over the last 25 years

“…In Wallonia, Belgium, negligible effects of season of calving were found on herd life (Froidmont et al, 2013), whereas in Spain survival rate was higher for heifers calving in winter and spring (Bach, 2011). These opposite results for season could be due to climatic differences, where cows in hot climates had impaired reproduction and also had lower survival rates in the hotter summer months (Vitali et al, 2009). Furthermore, national regulations, like the milk quota system, might have affected seasonal differences.…”

Metabolic and hormonal acclimation to heat stress in domesticated ruminants

“…This is mainly due to the various combinations of factors such as temperature, humidity, wind and direct and indirect radiations. A plethora of biometeorological indices has been developed and these empirical formulas would ideally predict the weather conditions when ruminants start to experience heat stress (Bohmanova et al, 2007) and become susceptible to heat-induced death (Vitali et al, 2009). Most temperature-humidity indices (THIs) are a combination of only ambient temperature (often referred to as dry-bulb temperature) and relative humidity.…”

“…High temperatures may cause heat stroke, heat exhaustion, heat syncope, heat cramps and ultimately organ dysfunction, and these heat-induced complications occur when the body temperature rises approximately 38C to 48C. Our recent epidemiological dairy cow study (Vitali et al, 2009) indicates that 80 and 70 are the daily maximum and minimum THI values, respectively, above which heat-induced death rate increases. In addition, 87 and 77 are the daily upper critical maximum and minimum THI, respectively, above which the risk of heat-induced death becomes maximum (Figure 2).…”

“…Indirect influences include those derived from reduced nutrient intake, altered microbial populations (around and in the animal), redistribution of vector-borne diseases, decreased host resistance to infections, water shortages and food-borne diseases. A series of studies have described a higher risk of mortality during the hottest months (Dechow and Goodling, 2008;Vitali et al, 2009), and an increased death rate during extreme weather events (Hahn et al, 2002). High temperatures may cause heat stroke, heat exhaustion, heat syncope, heat cramps and ultimately organ dysfunction, and these heat-induced complications occur when the body temperature rises approximately 38C to 48C.…”

Dairy cattle in a temperate climate: the effects of weather on milk yield and composition depend on management

“…High temperatures are associated with a greater incidence of heat stress in livestock, which can have negative effects on milk yield (Bohmanova et al, 2007;Hammami et al, 2013), fertility (Hansen, 2009) and health , and increase the risk of mortality (Vitali et al, 2009). Heat stress occurs when animals experience conditions above their thermal comfort zone and are unable to dissipate enough heat to maintain † E-mail: davina.hill@sruc.ac.uk Animal (2015), 9:1, pp 138-149 © The Animal Consortium 2014 doi:10.1017/S1751731114002456 animal 138 thermal balance (Kadzere et al, 2002).…”