Genome-wide association study of gestation length in German Holsteins

Gestation length (GL) is important in seasonal calving systems and in the calving trait complex, because it affects traits such as stillbirth (SB) and calving ease. Utilizing imputed high-density genotypes from 34 497 German Holstein cows, this study aimed to identify genomic regions associated with GL. For this, a genome-wide association study (GWAS) was conducted, and the results were interpreted by searching for previously reported adjacent quantitative trait loci (QTLs). Four GL traits were analyzed: the direct calf effects on GL in first (GL_d1) and second (GL_d2) parity, along with the maternal effects on GL in first (GL_m1) and second parity (GL_m2). GWAS of direct effects on GL resulted in significant variants on BTA14, 18, and 19 for GL_d1, and on BTA18 and BTA19 for GL_d2. Regarding the maternal effect, only one variant on BTA19 was significant in the second parity. Adjacent to significant variants were known QTLs for several reproduction traits including SB. Overall, the study provides insights into the complex genetic architecture of GL in German Holstein cattle. The identified genomic regions are supported by previous studies and thereby strengthen the basis for future research.