The Use of a High Density 600K SNP Array for Identifying Genomic Regions Associated with Polycerate Traits in Jacob and Navajo-Churro Sheep

A genome-wide association study (GWAS) was undertaken to identify genomic regions for unique traits in Navajo-Churro and Jacob sheep.  These two breeds of sheep are polycerate (multi-horned) animals where the number of horns ranges from one to six. A split upper eyelid deformity (SUED) is also present in these breeds. Genomic DNA was collected from 37 Navajo-Churros and 23 Jacob sheep and genotyped with the Illumina Ovine Infinium HD SNP BeadChip. Horn type ranged from polled to five horns with the most common phenotype either polled (10) or four horned (22).  Scurs (incomplete bone growth) were also present and the most common combinations were two upper scurs (12) and two upper horns/two lower scurs (7).  The polled trait has been previously mapped to the ovine chromosome 10 (OAR 10); GWAS for polled versus horned animals reconstituted this association signal.  The most significant association with markers in the OAR10 region occurred when only polled and four horned animals were included in the analysis, suggesting that the four horned condition is the ancestral phenotype in these two breeds.  An analysis to search for the genomic region controlling the presence of two versus four horns returned a significant region on OAR 1 (142 Mb).  All findings need to be confirmed with additional animals.  Ten animals in this flock demonstrated at least one eye with SUED and eight of the ten animals (80%) had at least one scur. Interestingly, the polled condition and an atypical eyelash-and-eyelid phenotype are in perfect association in cattle.