Acid-base balance and morphological composition of blood in high-producing dairy cows under cold stress

The efficiency of milk production is based on the use of high-yielding dairy cows, particularly the black-and-white Holstein breed, which are kept using a loose-box housing system in large frame-type barns. The microclimate of these barns is significantly influenced by climatic conditions, which, during the winter period, can cause cold stress in the cattle. This stress leads to diseases and a decrease in milk productivity. The experiment assessed the temperature-humidity parameters of the macro- and microclimate of a large frame-type barn designed for 1,000 cows during the coldest period of the year. It also examined the impact of cold stress on the morphological composition and acid-base balance of blood in high-producing cows depending on their lactation stage and daily milk yield. It was found that the greatest cooling of the atmospheric air occurs between midnight and 6:00 AM, reaching -21.6 degrees. This results in a decrease in barn air temperature to subzero levels and a temperature-humidity index of 35 units, which corresponds to the zone of mild cold stress for cows. The temperature of the feed and water depends on the air temperature in the barn and is considered uncomfortable for cows during the coldest period of the year. During short-term cold stress, cows in their first lactation with a daily milk yield of 35–40 kg, as well as cows in their second and third lactations regardless of milk productivity, experience a decrease in leukocyte count by 34.4–41.7%. With the increase in the age of cows up to the third lactation, short-term cold stress causes a reduction of 12.8–17.1% in segmented neutrophils in the blood. Mild cold stress leads to a decrease in the partial pressure of CO2 in the blood of first-lactation cows regardless of milk productivity. In cows, regardless of milk productivity and lactation stage, cold stress results in a negative shift in buffer base, which, considering the blood pH level, indicates the development of metabolic acidosis under a high-energy feeding regimen. The obtained research results can serve as the basis for developing measures aimed at adapting high-yielding Holstein cows during the coldest period of the year in frame-type barns with sharp daily temperature fluctuations.