Assessment of the influence of meteorological factors on milk yield and component composition of milk of holstein cows

In many countries, much attention is paid to assessing the detrimental effects of high ambient temperatures on the livestock sector, which is aggravated by the effects of climate change. Dairy cattle are most susceptible to heat stress, which negatively affects milk yield and quality, reproductive capacity, immunity and life expectancy of animals. In this study, the effect of heat stress on milk yield and component composition of milk of Holstein cows was studied and quantitatively assessed. To determine changes in daily milk yield and qualitative composition of milk as a result of heat stress, the temperature-humidity index was calculated followed by one-way variance analysis, which made it possible to identify the degree of influence of meteorological factors on milk productivity of cows. An increase in ambient temperature to 24.6 °C (THI=65.2–74.5) provoked a decrease in milk yield by 1.2–2.5 kg (p<0.01; p<0.001), which indicates the development of heat stress in cows. High severity of heat stress in animals was noted at 30.3 °C (THI=75.4–82.3), when daily milk yield decreased by 5.6–8.1 kg (p<0.001). A decrease in fat content in milk was also noted – by 0.12–0.41% (p<0.01; p<0.001) and protein – by 0.07–0.11% (p<0.01; p<0.001). The strength of the influence of meteorological factors on the level of daily milk yield, milk fat and milk protein yield was the greatest and amounted to 25.35–43.49%. This allows us to obtain new knowledge about the threshold values of THI under certain weather conditions, when a negative effect of heat stress on the milk productivity of cows is noted.