Haplotypes affecting stillbirth and fertility in Icelandic Dairy Cattle

In the last decades, the rate of stillbirths in the Icelandic Dairy Cattle population has increased. Some of these stillbirths may be caused by recessive lethal mutations segregating in the population. These alleles can be identified by detecting homozygous haplotype deficiency (HHD) in genotyped animals. The aim of this study was to find genomic regions affecting stillbirth and fertility in the Icelandic Dairy Cattle population. We analysed genotypes from 20,557 animals with 35,481 autosomal markers. We identified HHD segments and estimated their effects on stillbirths and insemination failure, measured as non-return rates. We conducted genome-wide association studies (GWAS) for stillbirth and five fertility traits: interval from first to last inseminations, conception rate, number of inseminations, calving interval and infertility. While no GWAS association reached the genome-wide significance threshold, some of the top signals co-located with HHD haplotypes. A total of 19 haplotypes significantly either decreased fertility, or increased incidence of stillbirths, or both. Two HHD regions on BTA13: 43,577,221-59,026,521 and BTA8: 83,276,598-84,472,391 were associated with both lower fertility and higher incidence of stillbirths. We found no evidence of large structural variations in or around the HHD regions, suggesting that these signals are likely due to single loss-of-function mutation or small structural variations. Further research should focus on exploring these regions using whole genome sequence data.