The dissertation covers a comprehensive study and new data on economically valuable traits of Black-and-White cattle in high producing herds. The patterns of the formation of milk production traits of animals under the impact of various environmental and genetic factors as well as the manifestation of phenotypic traits were determined. The relative variability of individual economically valuable traits in cows and their offspring of different generations was investigated. The traits that correlated significantly with production were found and their effective use in breeding work with dairy cattle was recommended. The families were evaluated for their productivity and breeding value, genetic potential of the cows, the level of its utilization as well as the level of annual genetic progress in the milking herds were determined.
It was found that cows of all generations during the growing period at the age of 6, 12 and 18 months had better live weight compared to Ukrainian standards for Black-and-White and Holstein breeds. Additionally, the animals of “Stepnoy Breeding Plant” (PJSC) according to this indicator were much better than the heifers of the same age in “Veleten” (LLC). In terms of live weight, average daily gain, multiplicity of increase in live weight, coefficients of its growth and relative growth rate, the ancestors showed worse results as compared to the offspring of the first, second and third generations.
First-lactation cows were characterized by proportional development of the barrel, were quite tall and long with deep and ample chests, had a clearly expressed milk type, as indicated by the body structure indices calculated by us. In all the investigated measurements, except for the width of hook bone in cows of all generations and the girth of the shank in granddaughters and great-granddaughters, they outperformed the target parameters of the conformation traits for the first-lactation cows of the desired type of Ukrainian Black-and-White dairy breed. Smaller conformation dimensions of the offspring compared to their ancestors are explained by the younger age of the first calving for daughters, granddaughters and great-granddaughters. However, the most significant differentiation was observed in the width of the chest and oblique length of the barrel.
Breeding stock of the observed herds was characterized by average fertility efficiency, as indicated by the index with the same name (43,0–45,5) and the yield of calves per 100 cows (87,1–93,0). With each next generation, the reproductive ability of the animals improved, and the live weight at the first insemination and after the first calving decreased, which is due, as already noted, to the younger offspring in the related physiological periods. Low unreliable relative variability of the studied traits of cows and their offspring indicates a low level of inheritance of the reproductive features by the offspring.
Milk production in cows for seven lactations in the observed herds ranged from 7513,4 to 9551,8 kg. The cows were likely to perform worse as compared to their daughters, granddaughters, and great-granddaughters regarding milk production, milk fat and protein amount, while at the same time they performed better (most significantly) in fat and protein content in milk. The direct relations between milk production and live weight and conformation dimensions as well as inverted highly probable regarding the age of animals at first insemination and first calving give basis to affirm the efficiency of the indirect selection of heifers with these traits. The highest production was recorded in first-calving heifers born in spring or summer and calved in summer or fall. Among environmental factors, the most significant influence on milk production had the year of birth (27,5–42,5 %) and the year of the first calving (28,8–41,2 %).
