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

Vagner A. Benedito

Committee Member

Jianbo Yao


Gastrointestinal nematode parasitism is a top health concern for sheep producers worldwide as traditional means of treatment are becoming less effective. Haemonchus contortus is of particular interest because it feeds on blood, causing significant pathological problems in the host. Certain breeds of sheep, like St. Croix, are more naturally resistant to parasitism. However, the underlying mechanisms that result in resistance are not fully understood. The following two experiments evaluated qPCR differential gene expression during the first ten days of a challenge H. contortus infection from lymph node and abomasal tissues. Experiment 1 evaluated 24 St. Croix hair lambs and 24 Crossbred wool lambs across four experimental days (0, 3, 5, and 7). Wool animals expressed higher levels of genes associated with tissue remodeling, wound healing, and inflammation, but no expression of key Th2 cytokines. Hair sheep expressed genes more closely related to Th2 immune responses. Experiment 2 assigned 12 St. Croix hair lambs and 12 Suffolk crossbred wool lambs into two groups: naive control and day 10 challenge. No genes were differentially up-regulated in hair animals. Wool animals, however, expressed Th2 genes such as interleukin-4 and arginase-1. Results from these two experiments indicate an adaptive immune response as early as 3 days post challenge infection in hair sheep. Thus, the rapid protective immunity generation of parasite-resistant hair sheep is a key difference by which these animals reduce larval load and prevent establishment of adult parasites.