Finding candidate genes associated with milk-fat composition and non-coagulation of milk were the main goals of this thesis. First genetic correlations between winter and summer milk-fat composition of Holstein Friesian cows allowed to treat these as genetically the same trait. Based on these results, I performed a genome-wide association study (GWAS) with imputed 777,000 single nucleotide polymorphism (SNP) genotypes and identified 5 mega-base pairs on Bos Taurus Autosome (BTA) 17 associated with milk-fat composition. Furthermore, I fine-mapped BTA17 with imputed sequence data, which improved the resolution of the 5 mega-base pairs resulting in identification of the LARP1B gene as candidate gene associated with milk-fat composition. Second, I performed a GWAS with 777,000 SNP genotypes in Swedish Red cows, and identified a genomic region covering 7 mega base-pairs on BTA18 strongly associated with non-coagulation of milk. Haplotypes were built, genetically differentiated by means of a phylogenetic tree, and tested in phenotype-genotype association studies. These analyses resulted in identification of the VPS35 gene as candidate gene associated with non-coagulation of milk.