148 Does Increased Gametic Variance Translate to Increased Heterogeneity in progeny?

Abstract

Abstract The expected genetic merit of a new-born calf is simply the average genetic merit estimates of its parents. Parents with a very heterogenous genotype could, however, potentially generate a more heterogenous group of progeny than parents with a more homogenous genotype. The objective of the present study was to test this hypothesis, and a secondary objective was to determine the expected progeny variability in their estimates of genetic merit for traits associated with dairy-beef production based on their expected genomic heterogeneity. Gametic variance for calving difficulty, calf mortality, gestation length, docility, feed intake, and carcass weight, fat, and conformation was estimated for 22,038 beef sires of multiple breeds. Sire gametic variance per trait was estimated for each chromosome from all heterozygous single nucleotide polymorphisms (SNP), their location within the genome, and the estimated effect of each SNP on each trait. Gametic variance was estimated for the whole genome as the sum of the estimated gametic variance of all chromosomes. Individual progeny phenotypic records for each trait were adjusted for animal sex, dam parity and dam genetic merit for the trait, heterosis, recombination loss, and contemporary group. The correlations between sire estimated gametic variance and the standard deviation of his (adjusted) progeny phenotypes were then estimated for all sires with at least 20 progeny records; the number of genotyped sires with at least 20 progeny ranged from 2,395 (heifer calving assistance) to 8,545 (calf mortality). The mean gametic variance, relative to the variance of sire genetic merit, for heifer calving difficulty, cow calving difficulty, calf mortality, gestation length, docility, feed intake, carcass weight, carcass conformation, carcass fat were 0.0002, 0.0005, 0.09, 0.07, 0.30, 0.02, 0.25, 0.05, and 0.12, respectively. With the exception of carcass fat and carcass weight, the correlations between the estimated gametic variance per sire and the standard deviation of his (adjusted) progeny phenotypes were non-existent (-0.06 to 0.04); the correlations between the standard deviation of the adjusted progeny phenotypes and the gametic variance for carcass fat and carcass weight were 0.29 and 0.16, respectively. The (weak) correlations between gametic variance and progeny phenotypes for carcass fat and carcass weight suggest that greater gametic variance is associated with increased progeny heterogeneity for both carcass traits. Nevertheless, accounting for gametic variance when selecting beef bulls for use on dairy females seems to provide little benefit.