Utah State University
Identification of Genetic Regions Influencing Foot Rot in Sheep
USU personnel will travel to farms for diagnosis of footrot and collection of samples. It is anticipated that multiple flocks will need to be sampled in order to collect 100 affected and 100 matched control animals. However, additional travel funds will be provided by the USU College of Agriculture if travel expenses exceed $2,000. Blood collection supplies include needles and vacutainer tubes, as well as diagnostic testing by the Utah Veterinary Diagnostic Laboratory at $15/sample. Standard chemicals and supplies will be used for the DNA extraction, which an undergraduate student technician will perform under the direction of Ms. Tracy Hadfield, the senior technician in Dr. Noelle Cockett’s laboratory. All samples will be genotyped by Gene Seek using the Ovine SNP50 Bead Chip at $150/sample. Analysis of the data will be conducted by Ms. Hadfield
and Dr. Cockett.
Identification of Genetic Regions Influencing Footrot in Sheep
Stephen N. White1, Tracy S. Hadfield2, Anne Lichtenwalner3, Richard J. Brzozowski4, C. Thomas Settlemire5, Susan B. Shoen6 and Noelle E. Cockett2
1 USDA-ARS Animal Disease Research Unit, Washington State University, Pullman, Washington 99164-6630 USA
2 Department of Animal, Dairy and Veterinary Sciences, Utah State University, Logan, Utah 84322-4700 USA
3 Department of Animal and Veterinary Science, University of Maine, Orono, Maine 04469-5735 USA
4 Cooperative Extension, University of Maine, Falmouth, Maine 04105 USA
5 Departments of Biology and Chemistry, Bowdoin College, Brunswick, Maine 04011 USA
6 Falmouth, Maine 04105 USA
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 85 animals from four flocks, of which 26 animals had evidence of classic footrot with necrotic tissue in at least one hoof, 31 had intermediate footrot scores with some inflammation and/or discoloration (possibly early or resolving positives), and 28 were negative based on the absence of infection/inflammation in all four hooves. Case-control matching accounted for farm, breed (Merino, Katahdin, Tuni or unknown), sex, and an age category (lamb, yearling or adult). Linear regression analysis of disease score was performed using PLINK with a genome-wide significance threshold of 5x10-8. Initial analyses revealed a genome-wide significant SNP on ovine chromosome 18 (P=3.6x10-8). Ongoing analyses include a search for candidate genes in this genetic region of the emerging sheep genome assembly and additional association testing with larger animal sets.