A family pedigree is being developed that will contain 300 to 400 cattle phenotyped for host susceptibility to tick and hornfly infestation. Genomic DNA is being collected and stored on each phenotyped individual for future gene mining. A hypothesis has been proposed that suggests that the distribution of hornflies on individual cattle is the result of experiential host finding that is based upon obtaining a successful blood meal. Initially we will investigate biochemical and molecular associations between variants of the hornfly anticoagulant molecule, thrombostasin, and variants of bovine prothrombin.