Influence of air temperature during the summer on milk yield of Holstein cows

Abstract

The aim of this work was to evaluate milk yield losses directly influenced by the climate without the use of installments’ resources to heating and/ or cooling in a dairy farm. Twenty Holstein cows with an average body weight of 480 kg and different lactation stages were used. The milk yield to each animal and the air temperature during milking were measured for 30 days, twice a day, in the morning and in the evening milking. The cows were divided in three groups, as follows: GROUP L – cows in different lactation periods; GROUP PL – cows in the peak of lactation; GROUP P – cows in the first lactation. Data of milk production were submitted to an analysis of variance, considering the effects of days of observation, of the groups of the animals in each period (morning and afternoon) and considering the air temperature as a covariable of the model. The Pearson correlation was estimated (P<0.05) between the air temperature and the milk yield, as well as the heat transfer by sensible and latent flows between the cows and the environment to both periods evaluated. There was a significant difference (P<0.05) for milk yield among the morning and afternoon milking to all the groups studied. There is a negative and significant correlation (P<0.0001) of the air temperature on milk yield, measured as kg of milk. The inefficiency of heat dissipation due to an increase of air temperature makes the afternoon period critical to the milking of cows. Therefore it is necessary to use acclimatization systems to decrease the negative impact of air temperature on the performance of dairy cows