Reasons for the culling of cows depending on the level of homozygosity and genomic inbreeding of fathers

The causes of cow mortality were studied depending on the level of homozygosity and genomic inbreeding of sires. Genomic data from 307 Holstein and Black-and-White bulls with 34,280 daughters were used. To calculate the homozygosity level (Ca), a multiplex panel of 12 microsatellite loci was used: TGLA227, BM2113, TGLA53, ETH10, SPS115, TGLA122, INRA23, TGLA126, BM1818, ETH3, ETH225, BM1824 with direct calculation of individual homozygosity as the ratio of the number of homozygous loci to the total number of analyzed loci with complete data. For genomic inbreeding (FROH), the Illumina Bovine SNP50K v2 BeadChip with a density of 54,609 SNPs was used, FROH was calculated as the ratio of the sum of all ROH lengths in millions of nucleotide pairs (mb) in the sire genome to the total genome size in mb for 29 bovine autosomes overlapping the SNPs, expressed as a percentage. With increasing Ca, the mortality rate of cows due to limb diseases increases by 0.882 %. Other most significant causes in percentage terms include: difficult births and complications, an increase of 0.263 %, osteomalacia by 0.172 %, zoobrak by 1.818 %, other non-infectious diseases by 0.533 %, mastitis 0.384 %. With the increase of FROH, the percentage of animals leaving for the following reasons increases: limb diseases by 2.019 %, difficult labor and complications by 1.471 %, gynecological diseases by 0.964 %, respiratory diseases by 0.146 %, udder atrophy 0.696 %, bursitis 0.364 %, mastitis 0.774 %, ketosis by 0.044 %, zoobrak by 4.841 %, arthritis by 0.394 %, and other reasons. It can be stated that the frequency of leaving in groups of inbred animals increased by 0.011–4.840. A reliable difference was noted between the groups for all samples according to the Bartlett criterion and Cochran's g-test at a significance level of α = 0.05. All calculated Pearson Chi-square values in all groups were less than critical, and the p-value was more than 0.05.