Veterinarija ir Zootechnika

The survey was conducted on a Bulgarian farm with 500 Holstein-friesian dairy cows housed in free-stall dairy operation. Measurements of carbon dioxide (CO2) levels were taken in 2x8 "Herringbone" milking parlor. Monthly within a year, during the morning, midday and evening milkings measurements were taken at the beginning, half-way through and at the end of the milking of the herd. Carbon dioxide levels were monitored with a Lutron MCH-383SDB (Lutron Electronic Enterprise Co., LTD., Taiwan) . At the same time, the temperature-humidity index (THI) levels were recorded using the “Kestrel 5400” Weather Meter (Kestrel Instruments, USA) . The highest average values of carbon dioxide in the air of the milking parlor were recorded in the winter season (756.67 ppm), and the lowest in the summer season (435.8 ppm). The highest recorded THI values were in the summer - 72.8, and the lowest in the autumn - 53.5. The highest CO2 values were found at THI levels around 50, established in autumn and winter, because ventilation in the milking parlor was poor.