Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Animal and Nutritional Sciences

Committee Chair

Scott A Bowdridge

Committee Co-Chair

Robert Dailey

Committee Member

Robert L Taylor Jr


Gastrointestinal nematode parasitism is the greatest problem facing small ruminant livestock, largely due to development of anthelmintic resistance. Of particular concern is Haemonchus contortus, a hematophagous trichostrongylid that can lead to death in lambs or immunocompromised sheep. Some breeds of sheep are resistant to Haemonchosis, e.g. St. Croix (STC) hair sheep. St. Croix sheep have well-documented resistance and have been shown to develop a robust immune response, generating a rapid cellular response to larval stages that does not occur in susceptible sheep. Studies evaluating effects of mononuclear cells, including monocytes and lymphocytes, indicate that these cells dramatically reduce motility of H. contortus larval motility in vitro. Furthermore, breed affected larval motility. However, lack of motility may also have been caused by immune cell trapping. In this study, the impact of peripheral blood mononuclear cells (PBMC) on H. contortus larvae in the presence or absence of autologous serum was measured by larval ATP. Viability of larvae was tested by measuring fecal egg count (FEC) after infecting susceptible sheep with PBMC-exposed larvae. Larvae exposed to STC-derived or Suffolk (SUF)-derived PBMC had lower (P < 0.001) ATP than live larvae (0.12 muM ATP and 0.16 muM ATP) (0.27 muM ATP). Larvae exposed to PBMC from both breeds were greater than dead larval ATP (0.03 muM ATP) (P < 0.001). Larval ATP was lower when exposed to STC-derived PBMC with serum (0.11 muM ATP) than SUF-derived PBMC with serum (0.23 muM ATP) or live (0.22 muM ATP) (P < 0.001). There was no significant difference between live larvae and larvae treated with SUF-derived PBMC with serum. Taken together, these data indicate a cellular response alone is capable of significantly lowering larval ATP. However, the addition of serum to SUF-PBMC failed to reduce larval ATP, suggesting differences in humoral response in mediation of H. contorus..