Abstract
BackgroundManaging beneficial Mendelian characteristics in dairy cattle breeding programs implies that the correlated genetic effects are considered to avoid possible adverse effects in selection processes. The Mendelian trait polledness in cattle is traditionally associated with the belief that the polled locus has unfavorable effects on breeding goal traits. This may be due to the inferior breeding values of former polled bulls and cows in cattle breeds, such as German Simmental, or to pleiotropic or linkage effects of the polled locus.MethodsWe focused on a variance component estimation approach that uses a marker-based numerator relationship matrix reflecting gametic relationships at the polled locus to test for direct pleiotropic or linked quantitative trait loci (QTL) effects of the polled locus on relevant traits. We applied the approach to performance, health, and female fertility traits in German Simmental cattle.ResultsOur results showed no evidence for any pleiotropic QTL effects of the polled locus on test-day production traits milk yield and fat percentage, on the mastitis indicator ‘somatic cell score’, and on several female fertility traits, i.e. 56 days non return rate, days open and days to first service. We detected a significant and unfavorable QTL effect accounting for 6.6% of the genetic variance for protein percentage only.ConclusionsPleiotropy does not explain the lower breeding values and phenotypic inferiority of polled German Simmental sires and cows relative to the horned population in the breed. Thus, intensified selection in the polled population will contribute to increased selection response in breeding goal traits and genetic merit and will narrow the deficit in breeding values for production traits.
Highlights
Managing beneficial Mendelian characteristics in dairy cattle breeding programs implies that the correlated genetic effects are considered to avoid possible adverse effects in selection processes
The means for the production traits clearly reflect the phenotypic inferiority of polled animals, e.g. horned cows produced 2.71 kg and 4.40 kg more milk on average than polled Pp and PP animals, respectively
The moderate estimates of the heritability obtained for the test-day production traits milk yield (MY), F% and P% and the low estimate of the heritability for test-day somatic cell score (SCS) are in line with previously reported estimates in the German Simmental population [32, 33]
Summary
Managing beneficial Mendelian characteristics in dairy cattle breeding programs implies that the correlated genetic effects are considered to avoid possible adverse effects in selection processes. The Mendelian trait polledness in cattle is traditionally associated with the belief that the polled locus has unfavorable effects on breeding goal traits. The broad availability and use of the high-throughput genotyping technology in cattle have enhanced the discovery of new Mendelian genetic characteristics during the past decade [9]. Most of these relevant genetic characteristics are lethal recessive monogenic disorders (e.g. cholesterol deficiency (CDH) [10]) or detrimental recessive haplotypes with unfavorable effects on production and functional traits It is important to examine the pleiotropic or linked effects of the desired alleles before aiming for their fixation
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