Doctor of Philosophy (PhD)


Veterinary Medical Sciences - Pathobiological Sciences

Document Type



Haemonchus contortus is one of the major nematode parasites causing substantial economic losses in small ruminant farming worldwide. Recently, effect of anthelmintic treatment has decreased due to an increasing problem of nematode populations that have developed resistance to anthelmintics. There are certain breeds of sheep that are identified as being relatively resistant to the parasite including Gulf Coast Native (Native) sheep. Understanding the mode of immune response that helps these breeds of sheep control infection could help design vaccines and enhance control programs. This experiment was designed to evaluate the immunological responses of Native, compared with susceptible Suffolk sheep that might be responsible for this resistance. In Experiment 1, groups (n = 5) of 6 month old Native and Suffolk lambs were given infective larvae as one time (bolus) or trickle experimental infections. Fecal, blood, and serum samples were collected. Abomasal mucosa samples were collected at the time of necropsy on day 14 and day 21. There was no significant difference in number of worms recovered at necropsy but the ratio of adult vs larvae was significantly greater in bolus infected Suffolk than Native. Native lambs had significantly greater numbers of mast cells and eosinophils in the abomasal mucosa and serum IgG production was significantly greater compared to Suffolk lambs. Native lambs also showed a trend of increased level of serum IgA and IgE compared to Suffolk lambs. In Experiment 2, immune responses were evaluated in naturally infected Native and Suffolk lambs that grazed pasture contaminated predominantly with H. contortus. Ten lambs of each breed grazed together for 42 days. Fecal, blood and serum samples were collected. Five lambs of each breed were necropsied on day 35 and five on day 42 for nematode recovery and abomasal tissue sample collection. Native lambs had significantly lower FEC, significantly lower PCV reduction percent, and significantly higher serum IgE after day 14 and increased expression of Il-4 on day 10 post exposure compared to Suffolk lambs. At both necropsy time points, Native lambs had significantly greater numbers of mucosal mast cells, eosinophils and globule leukocytes in abomasal mucosa than Suffolk lambs.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

James E. Miller