Assessment of the influence of the level of homozygosity and genomic inbreeding of holstein and black-pied stud bulls on dairy productivity indicators and reproduction of daughters

A study was conducted to investigate the impact of genomic inbreeding (FROH) and the level of homozygosity (Ca) on milk productivity and reproduction. To assess the impact of FROH, data on SNP markers from 196 sires were used; FROH was then assigned to daughters (n=64,027). FROH was calculated as the ratio of the sum of all lengths of homozygosity patterns (ROH) in million nucleotide pairs (mb) in the sire genome to the total genome size in mb for 29 bovine autosomes overlapping SNPs, expressed as a percentage. To calculate the impact of inbreeding (Fx), 196 bulls and 64,027 daughters were used, and Ca for STR markers from 228 bulls and 80,849 daughters was used. To assess the influence of the cows' own Fx, a dataset of 39,276 heads was used. Fx was calculated using the WrightKislovsky formula, the Ca level as the ratio of the number of homozygous loci to the total number of analyzed loci. The optimal Fx level for obtaining high milk productivity indicators is the range of 0-3.125%. A high level of inbreeding (6.25-12.5%) negatively affects milk fat content. Thus, a reliable relationship was established between the level of inbreeding for STR markers and the productive qualities of daughters. From the point of view of milk productivity, the minimum level of inbreeding is optimal. All indicators demonstrate statistical significance (p=0.00). A systemic effect of genomic inbreeding on all the studied traits is observed, and the protein content indicator turned out to be the most sensitive. Reproductive qualities demonstrate a moderate dependence on the factor. As practical suggestions, it is possible to recommend using moderate classical inbreeding within 0-3.125%; control the level of genomic inbreeding in the range of 4.2-7.5% and take into account the level of homozygosity for FROH and STR markers when selecting pairs, as well as conduct reg ular monitoring of productivity and reproduction indicators.

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