Technical note: The role of circulating low-density lipoprotein levels as a phenotypic marker for Holstein cholesterol deficiency in dairy cattle.

With the recent discovery of a Holstein cholesterol deficiency (HCD) haplotype, the USDA has labeled many dairy animals as HCD carriers based on haplotype and pedigree analysis. We set out to investigate the effect of HCD status on various cholesterol transport molecules, namely low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol, and triglycerides in both males and females. A genome-wide association study was also conducted to narrow down the genomic region correlated with varying LDL-C levels. In the study, 34 HCD carrier animals showed significantly lower cholesterol and LDL-C levels compared with their 34 closely related, non-HCD controls. The genome-wide association study based on 73 animals using 56,198 SNP markers revealed an association with chromosome 11 in the region of 66,218,925 to 66,946,746 bp. We also tested the effect of HCD status on sperm quality traits using fresh ejaculates and frozen-thawed semen samples, but did not find any discriminating effects. Our study has demonstrated the use of LDL-C as a key phenotypic marker for determining HCD status in dairy cattle and this is the first study that clearly shows a cause-effect relationship of the HCD haplotype on circulating LDL-C.