Conditions for cold stress development in dairy cattle kept in free stall barn during severe frosts

The impact of low temperatures combined with higher velocity of ventilated air in winter during severe frost in a free stall barn on the development of cold stress in Holstein-Friesian breed dairy cattle was studied. The study included measurements of outside and inside air parameters and cows' milk yield. Cold stress was evaluated in three technological groups (TG) using the WCT (Wind Chill Temperature) index. During the research, significant temperature and wind velocity differences (by up to 5°C and 0.5 m/s) were recorded in three zones of the barn occupied by the individual TG. All this resulted in different values of WCT. During most severe frosts lasting for 9 days, the average air temperature in the barn was -8.9°C (the lowest value was -17.3°C). The calculated average operative temperature for cows from all TG was as follows: -7.0°C for TG1, -11.1°C for TG2, and -12.3°C for TG3. It was also observed that animals from TG2 suffered from mild cold stress, which resulted in milk yield reduction by approximately 2 kg. It was concluded that there is a strong correlation (r = 0.72-0.89 with P < 0.05) between milk production and the WCT index. The measurements of most important microclimate parameters in the barn were conducted during winter seasons over the period of 2 years. They led to the conclusion that cattle kept in free stall barns are not vulnerable to the combination of low temperature and increased air movements. Research results of the present as well as of other authors were the basis for developing a table determining operative temperature for cows depending on the temperature of the environment and air movement velocity. Yet, the calculations and analysis of results show that there is a need to improve the applied calculation formula for operative temperature during cold weather.