German Black Pied (DSN) is considered an ancestral population of the Holstein breed. The goal of the current study was to fine-map genomic loci for milk production traits and to provide sequence variants for selection. We studied genome-wide associations for milk-production traits in 2160 DSN cows. Using 11.7 million variants from whole-genome sequencing of 304 representative DSN cattle, we identified 1980 associated variants (-log10(p) ≥ 7.1) in 13 genomic loci on 9 chromosomes. The highest significance was found for the MGST1 region affecting milk fat content (-log10(p) = 11.93, MAF = 0.23, substitution effect of the minor allele (ßMA) = -0.151%). Different from Holstein, DGAT1 was fixed (0.97) for the alanine protein variant for high milk and protein yield. A key gene affecting protein content was CSN1S1 (-log10(p) = 8.47, MAF = 049, ßMA = -0.055%) and the GNG2 region (-log10(p) = 10.48, MAF = 0.34, ßMA = 0.054%). Additionally, we suggest the importance of FGF12 for protein and fat yield, HTR3C for milk yield, TLE4 for milk and protein yield, and TNKS for milk and fat yield. Selection for favored alleles can improve milk yield and composition. With respect to maintaining the dual-purpose type of DSN, unfavored linkage to genes affecting muscularity has to be investigated carefully, before the milk-associated variants can be applied for selection in the small population.
Keywords: GNG2; GWAS; MGST1; TLE4; TNKS; alpha S1-casein; fat content; lactation; milk yield; protein content; serotonin receptor.