Reproduction changes reaserch in dairy cattle after their calving.

Thesis Objective: to study and evaluate the reproductive efficiency of dairy cows in the period after calving. Methodology of study: studies were carried out in two dairy cattle farms. In March-May 2016, in the X farm of District X and in October 2018 in Y farm of Y district. During the first trial, 13 cows of first, 8 of second, and 8 of third lactation were selected on the farm X. The days after calving were recorded, rectal palpation of the genital organs was performed, where the size of the ovaries (length in mm, width in mm, and estimated total area in mm²) was measured using the ultrasonic “Draminski” apparatus, as well as the diameter of the follicles in mm. The study was conducted 6 times, every day of the week, following changes in ovaries and its functional derivatives during the period after calving. During the second test, the herd management program \"DairyPlan c21\" was used in Y farm to select the cows for the study. The groups consisted of 20 second lactation, 14 third lactation and 10 fourth lactation cows. The data of productivity (milk yield in kg), milk quality, age, calving, insemination, and morbidity were collected. Milk quality indicators consisted of the percentages of protein and fat and the amount of urea in the milk. The activity (in steps) was also tracked and recorded 7 days before the appearance of oestrus and insemination. Artificial insemination was carried out on the seventh day of activity. Screening for uterine inflammation cows was carried out 15 days after calving. After diagnosis, cows were regrouped to healthy (n = 10 second lactations, n = 4 third lactations, n = 4 fourth lactations) and non-healthy (n = 10 second lactations, n = 10 third lactations, n = 6 fourth lactations). The results of the study: The analysis of the dynamics of ovarian changes showed that the maximum difference in left ovarian area was (372.56 mm²) between the first and second lactation cows, 36 days after calving (p <0.01), while the difference in right ovary area was (243, 30 mm²) on day 43, between the first and third lactation cows (p