Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Animal and Nutritional Sciences

Committee Chair

Scott Bowdridge

Committee Member

Scott Greiner

Committee Member

Kimberly Barnes


With current pressures to seek out genetic solutions to combat antimicrobial resistance, genetic resistance to the gastrointestinal nematode Haemonchus contortus may reduce need for prophylactic antibiotic use. The Katahdin breed has effectively utilized post-weaning fecal egg count estimated breeding value (PFEC EBV) to reduce parasitism within their flocks, but there still remains significant opportunity for selection within breed. In a previous study, Katahdin sheep sired by low PFEC sires had greater survivability to weaning than lambs sired by high PFEC rams and preweaning was caused by other diseases than parasitism. Those data lead to the hypothesis that selection for PFEC also selects for improved generalized immunity. Therefore, the aim of this study is to compare effects of a divergent mating scheme based upon PFEC on antibody production in purebred Katahdin lambs. All lambs were managed as one cohort with dams running alongside their lambs until approximately 105 days of age. During this time on pasture a natural infection was established, blood samples were taken weekly, and fecal samples were collected bi-weekly. Lamb PFEC corresponded to sire type validated the divergent mating scheme. Circulating IgG was measured using an ovine-specific enzyme-linked immunosorbent assay (ELISA). These data indicate that lambs selected for low PFEC have greater abundance of circulating IgG than high PFEC-EBV lambs (LoPFEC, 886.79 ug/mL and HiPFEC, 465.15 ug/mL P < 0.001). A sire by week comparison indicated that low PFEC lambs had greater magnitude of circulating IgG after booster vaccination, at week five (P < 0.001). Taken together these data indicate that PFEC values may be used as a predictor of immunological fitness outside the context of parasitic infections and has implications for use in selection towards individuals less prone to subclinical disease, therefore, limiting the need for antibiotic use.