PSIV-16 - Genome-Wide Association Study of Rambouillet Rams with Angular Limb Deformities

Lameness and limb deformities can be detrimental to range and breeding sheep. Growing animals are at an increased risk of angular limb deformities (ALD) and lameness, which adversely affects their mobility, breeding soundness and ultimately longevity. Ram testing allows developing ram lambs from different farms to be evaluated together under a consistent nutritive and environment management system. The aim of this study is to investigate rams from four ram test cohorts (North Dakota State University and University of Wyoming in two consecutive years) for genetic associations with ALD occurrence. In total 131 Rambouillet rams, including 17 ALD-affected and 114 unaffected, were genotyped using Axiom^TM Ovine Genotyping Array (50K). A genome-wide association study was conducted using a recessive chi-square model with correction by principal component analysis (eigenstrat). A marker on chromosome eight is significantly (unadjusted P-value= 1.74e-08) associated with the incidence of ALD. This marker is located within the gene; branched chain keto acid dehydrogenase E1 subunit beta (BCKDHB). BCKDHB is associated with mitochondrial membranes and metabolism which is required for effective bone (osteoblast and chondrocytes) formation. It is proposed that altered branched amino acid metabolism in rapidly growing sheep with this genotype may impart risk of limb deformities classified as ALD. Identifying genetic associations with ALD in sheep may help detect animals with a higher propensity for ALD, which would provide producers with additional tools to make informed management and breeding decisions.