Effect of temperature and relative humidity on the milk production of dairy cows

Abstract

The aim of this study was to evaluate the influence of environmental housing conditions on the milk yield of dairy cows. Measurements were taken in the summer period from June to September, 2020 and in the winter period during January, 2021 on a large-capacity farm of Holstein Friesian cattle. Cows were housed in free stall barn with the lying boxes and selected during the second or third lactations, in the summer period from the 51st day to the 135th day and in the winter period from the 64th day to the 120th day of lactation. The average temperature in the housing was 23 °C in summer, and 7.05 °C in winter. The average THI (thermal humidity index) value in summer was 70.43, but during the day the THI values sometimes reached 75. The dairy cows were therefore exposed to heat stress during summer. Increasing THI and temperature values negatively affected the milk yield, as there was a negative correlation between both THI and milk yield (r = −0.641; p < 0.01) and temperature and milk yield (r = −0.637; p < 0.01). Milk production in winter was at 58.77 kg per day and in summer at 49.55 kg per day. In the summer, the milk had a significantly lower content of fat (p < 0.05), proteins (p < 0.001), lactose (p < 0.001), minerals (p < 0.001) and conversely, a higher number of somatic cells (p < 0.01). These results show that worse environmental conditions during the summer negatively affected the level of milk yield and the composition of the cows’ milk.