Semester

Spring

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Scott Bowdridge

Committee Member

Scott Greiner

Committee Member

Keith Inskeep

Committee Member

Eugene Felton

Committee Member

Amy Welsh

Abstract

Selection within and among breeds are strategies to mitigate the impact of parasitism given failing chemotherapeutics. While Texels have improved marketability compared to other parasite-resistant breeds, the mechanism by which Texels reduce fecal egg count (FEC) is unclear. The immune response to Haemonchus contortus (Hc) was compared in Texel, parasite-resistant St. Croix, and parasite-susceptible Suffolk sheep. Adult worms exposed to St. Croix- and Texel-derived peripheral blood mononuclear cells and serum in vitro had greater binding around the reproductive structures than Suffolk and worm egg release tended to be affected by breed (P = 0.09). Resistance in Texels may be caused by reduced worm fecundity. Genetic merit for parasite resistance can be predicted by FEC estimated breeding values (EBV). To validate the FEC EBV, Katahdin rams (n = 10) with High and Low FEC EBV were randomly mated to Katahdin ewes. Spring-born progeny were developed on pasture. Post-weaning, lambs (Year 1, n = 113; Year 2, n = 118) were dewormed, transported to the WVU Animal Science Farm, and infected with Hc for five weeks. At removal from pasture, FEC was lower in Low FEC-sired lambs (P < 0.05). When infected with Hc, a greater proportion of Low FEC-sired lambs had worm counts of zero (P < 0.05) and worm fecundity was lower (P < 0.05) compared to High FEC-sired lambs. Progeny FEC corresponds with sire FEC EBV. Low FEC-selected Katahdins may have an intermediary form of resistance where worm burden is limited and fecundity is reduced in worms that establish.

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