DNA extraction and genotyping of bull samples Semen straws from 848 Holstein-Friesian sires, repre- senting the Irish dairy germplasm in recent years, were collected for genomic DNA extraction. Semen was washed twice in phosphate buffered saline (pH7.4) and centrifuged. The resulting cell pellets were resuspended in 450 μl of pre-warmed extraction buffer (10 mM Tris pH8, 10 mM EDTA, 0.1% SDS, 100 mM NaCl) and 15 μl of 2-mercaptoethanol was subsequently added. Fol- lowing addition of 10 μl proteinase K (20 mg/ml), sam- ples were incubated for 15 minutes at 55°C. An overnight incubation at 60°C ensured complete lysis. DNA was extracted using the Maxwell® instrument (Pro- mega Corp., Madison, WT, USA) according to the man- ufacturer’s instructions. All SNPs were genotyped in the bull population by Sequenom® using the iPLEX Gold assay on a MassARRAY® platform http://www.seque- nom.com. As a quality control measure, genomic DNA representing twenty-five animals was genotyped in duplicate for each SNP. Concordance across all dupli- cates was 100%.