Calving traits and udder health related traits are functional traits with a substantial impact on dairy welfare and the economy of milk production. Hence, the identification of trait associated molecular genetic markers and the analysis of the molecular background of calving traits and udder health is essential to implement molecular genetic information in new breeding schemes and to improve breeding success.
In this study separate and combined linkage and linkage disequilibrium analyses were performed to map genetic loci on Bos taurus chromosome 18 (BTA18) that are associated with functional traits and conformation traits in the German Holstein population. Quantitative trait loci (QTL) affecting udder health, calving performance and udder conformation traits as well as body conformation traits were identified in the middle to telomeric region on BTA18. Overlapping QTL affecting udder health and udder conformation traits as well as the coincidence of QTL affecting calving performance and body depth, indicated that conformation traits might present a functional background underlying QTL affecting udder health and calving performance in the German Holstein population.
Further analyses of maternally inherited marker alleles indicated the two-marker-haplotype BB710 - PVRL2_c.392G>A and microsatellite marker DIK4234 to be in population-wide linkage disequilibrium to the causal mutations affecting udder health and calving performance, respectively. Specifically, the maternally inherited DIK4234 allele effects on maternal and direct effects on calving performance were positively correlated. This highlights the respective telomeric region on BTA18 for marker assisted selection for calving traits, because the positive correlation is in contrast to the genome-wide negative correlation of maternal and direct effects on calving traits reported for the German Holstein population.