Genome-wide association study for milking speed in Fleckvieh cattle

Milking speed is an important trait influencing the udder health of dairy cows, as well as labor efficiency. However, it has received little attention in genomic association studies. The main objective of this study was to determine regions and genes on the genome with a potential effect on milking speed in Fleckvieh (dual-purpose Simmental) cattle. Genome-wide association studies were conducted using deregressed breeding values of bulls as phenotypes. We found 6 SNPs on 4 autosomes that were significantly associated with milking speed for additive effects. Significant regions on BTA4 and BTA19 correspond with findings for other dairy cattle breeds. Based on the observations of Fleckvieh breed managers, variation of milking speed in batches of daughters of some bulls is much higher than in daughter groups of other bulls. This difference in within-family variation may be caused by the transmission of alternative alleles from bulls being heterozygous for a gene affecting milking speed. To check on this, we considered the SD of yield deviations in milking speed of half-sib daughters as a new trait and performed GWAS for dominance effects. One signal on BTA5 passed the genome-wide Bonferroni threshold that corresponded to the significant signal from standard GWAS on deregressed breeding values. The key conclusion of this study is that several strong genomic signals were found for milking speed in Fleckvieh cattle, and that the strongest of them are supported by similar findings in Brown Swiss and Holstein Friesian cattle. Milking speed is a complex trait whose subprocesses have not yet been elucidated in detail. Hence, it remains a challenge to link the associated regions on the genome with causal genes and their functions.