Genomic Evaluation for Clinical Mastitis in Czech Holstein

Abstract

Genomic breeding values for resistance to clinical mastitis (CM) have been estimated using a single-trait or multi-trait model; the latter comprised besides CM also linear udder traits and somatic cell count (SCC) transformed to somatic cell score (SCS). Dataset included 79,431 Holstein cows and 132,614 lactations with a lactation incidence of clinical mastitis for all lactations 19.91%. Cows calved between 2017 and 2021 in 104 herds. CM was defined as binary trait with 0 (no case) and 1 (at least 1 case) during the lactation, SCC as the average value per lactation. The linear type traits were udder depth, udder width, suspensory ligament, and udder’s subjective score in %. The single-step genomic method was employed to predict CM genomic breeding values (GEBV_CM). Linear model equations included the random additive genetic effect of animal and for CM and SCS fixed effects parity and age at calving class, herd-year-season of calving and random effect of the permanent environmental effect of a cow; for linear udder traits herd-year-season of scoring, classifier and linear and quadratic regression on the age at calving and the days in milk. Pedigree involved 208,217 animals. Number of genotyped animals was 35,472; effective animals 35,131; bulls 5,377, cows 14,941 and heifers 15,154. The final number of effective SNPs was 35,338. Variance and covariances included in the multi-trait model GEBV_CM prediction yielded heritabilities 0.22 udder assessment, 0.38 udder depth, 0.19 udder support, 0.16 udder width, 0.11 SCS, 0.04 CM; and genetic correlations between CM and udder assessment -0,30, udder depth -0,41, udder support -0,30, udder width, 0.11 SCS. The mean of GEBV_CM was 0.0047 and 0.0174 for the multi-trait and single-trait models, respectively. For bulls born in 2019 (235), the mean of GEBV_CM was -0.0241 and 0.0059 for the multi-trait and single-trait models, respectively. An increase in the reliability of the breeding value appeared in the multi-trait model compared to the single-trait model. The average reliability of GEBV_CM increased for young genomic bulls (235, born 2019) from 0.22 to 0.45; for genomic heifers (15,154) from 0.27 to 0.50.