Identification of Genetic Regions Influencing Footrot in Sheep

Footrot is a contagious hoof disease that begins as an infection of the interdigital skin of the hoof (interdigital dermatitis), followed by formation of lesions on the interdigital wall of the hoof and subsequent separation of the hard horn from the foot. Affected animals are obviously lame and prolonged disease appears painful. Footrot results in a substantial cost to sheep producers because of reductions in lamb growth and lambing percentage, treatment of affected animals, and annual prevention of the disease. Resistance and/or susceptibility to footrot appears to be genetically controlled in sheep based on evidence of differences among breeds for resistance versus susceptibility, the ability to genetically select for resistance to footrot, and a reported association between the incidence of footrot and variation in MHC class II genes.  As an initial step in the identification of genetic regions that influence footrot in sheep, genotypes for the Ovine SNP50 BeadChip were obtained for 87 animals from four flocks, of which 27 animals had evidence of classic footrot in at least one hoof, 29 had intermediate scores for footrot and therefore were possibly early or resolving positives, and 31 were considered negative based on the absence of infection/inflammation in all four hooves. Case-control matching accounted for farm, breed (Merino or Katahdin), sex, and an age category (lamb, yearling or adult).  Linear regression analysis of disease score was performed using PLINK software with a genome-wide significance threshold of 5x10^-8.  Initial analyses revealed a SNP on ovine chromosome 18 with a significance value of P=3.6x10^-8. This genetic region has been examined for candidate genes using information from the emerging sheep genome assembly, along with information in the genomes of humans, cattle and pigs. Analyses that include additional animals are ongoing.