Milk productivity of Holstein and black-and-white cows under heat stress

Due to the widespread warming of the climate and an increase in the duration of the hot, dry period, heat stress is becoming an urgent problem of dairy cattle breeding. Highly productive animals are most sensitive to temperature stress, during which their daily milk yields can decrease significantly. The aim of the research was to study the dynamics of milk yields of dairy cows during the first four months of lactation in the summer. The studies were carried out in two farms located in the zone of insufficient moisture in the Stavropol Territory. The first farm is engaged in breeding Holstein cattle, the second is a black-and-white breed. In each farm, 3 experimental groups of animals were formed, 10 heads each, with an average daily milk yield in the first month of lactation: I experimental group – up to 20 kg; I experimental group – 20-30 kg; I experimental group – more than 30 kg of milk. The value of temperature stress was determined based on daily temperature and humidity data. In May, the absolute majority of days corresponded to the optimal values of temperature and humidity for keeping dairy cattle in both farms. In June and August, days with minimal and moderate heat stress prevailed. The milk yield of animals in the first experimental group increased significantly over the months of lactation. The milk yield of the first and fourth months of lactation of animals of the III and III experimental groups did not significantly differ. Thus, in medium-and highly productive animals of Holstein and black-and-white breeds, with minimal and average values of thermal stress, there is no significant change in milk yield over the months of lactation.