Lack of evidence for bovine Y-chromosomal variation in beef traits. A Bayesian analysis of Simmental data

A Bayesian estimation of a Y-chromosomal variance component was carried out for four beef traits recorded on 218 535 Simmental young bulls in the Bava rian unconducted beef progeny test. Net gain and market value were analysed with a linear model and EUROP-grade and fatness-class using a threshold mo del with two categories. All autosomal paternal relationships of 6720 sires (6250 with recorded progeny) were taken into account in a sire model. The pedigree was traced back from recorded progeny to the founder of each pater nal line, resulting in 120 potentially different Y chromosomes. The number of generations bera een founder and recorded progeny ranged from one to sev en. In all cases the marginal posterior mean of the Y-chromosomal variance was very close to zero, and 0.1% or less of the total phenotypic variance w as due to the Y chromosome. For all traits the mode of the marginal posteri or distribution was on the left boundary of the parameter space suggesting that there is either only a very small or no Y-chromosomal generic variance at all far beet trues In German Simmental. Threshold-model heritabilities were 0.20 and 0.12 for EUROP-grade and fatness-class, respectively, with co rresponding standard errors of 0.003 and 0.009.