Improvement of breeding traits of cattle when using inbred and homozygous sires

Abstract

The use of inbred and homozygous sires reduces the share of variability in the biodiversity of the population when it occurs under uncontrolled management, which leads to a decrease in the heritability of the trait. Studying the features of the consequences of inbreeding of sires helps to make their evaluation on the quality of off spring more informative, because as a result of related mating, the genetic structure of the population changes. If a selection with the genotypes of an inbred sire, heterozygous for two aabb loci of body traits, is applied to a certain group of cows, then quantitative traits in the off spring will determine milk productivity. Positive variants should be considered omozygotes, in which dominance is manifested, and heterozygotes, i. e. approximately 70 % of off spring. The probability (frequency) of their appearance is high and one can count on a favorable combination of genes in off spring from inbred and homozygous sires, if the maternal population is heterozygous in terms of physique, which are associated with the level of manifestation of milk productivity. In the breeding herd of Holstein breed, the system of intra-linear selections and crosses of homo- and heterozygous sires revealed the disparity of milk yield increases, the mass fraction of fat and protein in milk in daughters relative to mothers. The superiority in the total yield of milk protein and fat for 305 days of the fi rst lactation of the group of daughters from intraline mating and homozygous sires over mothers was 82,6 (p < 0,01) and 112,9 kg (p < 0,01), respectively. The highest total rank according to the complex of breeding traits was assigned to the daughters of homozygous sires and then according to the increase in the indices of the genetic value of the traits of lactation, the group B was followed by the group derived at the crosses of the lines.