Polymorphisms within the APOBR gene are highly associated with milk levels of prognostic ketosis biomarkers in dairy cows

Essentially all high-yielding dairy cows experience a negative energy balance during early lactation leading to increased lipomobilization, which is a normal physiological response. However, a severe energy deficit may lead to high levels of ketone bodies and, subsequently, to subclinical or clinical ketosis. It has previously been reported that the ratio of glycerophosphocholine to phosphocholine in milk is a prognostic biomarker for the risk of ketosis in dairy cattle. It was hypothesized that this ratio reflects the ability to break down blood phosphatidylcholine as a fatty acid resource. In the current study, 248 animals from a previous study were genotyped with Illumina BovineSNP50 BeadChip, and genome-wide association studies were carried out for the milk levels of phosphocholine, glycerophosphocholine, and the ratio of both metabolites. It was demonstrated that the latter two traits are heritable with h2 = 0.43 and h2 = 0.34, respectively. A major quantitative trait locus was identified on cattle chromosome 25. The APOBR gene, coding for the apolipoprotein B receptor, is located within this region and was analyzed as a candidate gene. The analysis revealed highly significant associations of polymorphisms within the gene with glycerophosphocholine as well as the metabolite ratio. These findings support the hypothesis that differences in the ability to take up blood phosphatidylcholine from low-density lipoproteins play an important role in early lactation metabolic stability of dairy cows and indicate APOBR to contain a causative variant.

Cytogenetic and syntenic assignment of the bovine <i>platelet-activating factor receptor (PTAFR)</i> to cattle chromosome 2 (Brief report)

The platelet-activating factor receptor (PTAFR) encoding gene, also known as PAFR or PAFr, belongs to the rhodopsin gene family. The receptor binds the platelet-activating factor (PAF) that has been implicated as a mediator in diverse pathologic processes. In cattle, PTAFR is associated to the reproduction process and is described as a receptor that is involved in inflammatory-like processes of the uterus associated with increased vascular permeability (TIEMANN et al. 2005). The gene sequence was recently annotated on Bos taurus (BTA) chromosome 2 at 129.4 megabases in NCBI Bos taurus build Btau_4.0. The presented data confirm this annotation by independent physical mapping methods and anchor the corresponding DNA segment to the chromosome. PTAFR was assigned by fluorescence in situ hybridization (FISH) and somatic hybrid cell (SHC) mapping.