Immune mechanisms of Texel sheep to adult and egg stages of Haemonchus contortus.

Experimental Haemonchus contortus (Hc) infections revealed that Texel sheep have faecal egg counts (FEC) comparable to parasite-resistant St. Croix but adult worm burden comparable to parasite-susceptible Suffolk sheep. The aim of these studies was to further investigate the mechanism causing this disparity. Cellular and humoral immune responses to adult- and egg stage Hc were compared amongst St. Croix, Texel and Suffolk sheep. Adult worms and eggs were exposed to peripheral blood mononuclear cells (PBMC) and serum from the three breeds in vitro. There was a greater IgA binding to eggs when treated with St. Croix and Texel serum (p < .05), and these eggs exhibited a lower hatch rate (p < .05) when exposed to serum and PBMC. Adult worms exposed to St. Croix and Texel-derived PBMC, and serum had greater binding around the head and reproductive structures than worms exposed to Suffolk-derived cells and serum. Consequently, egg release tended to be affected by breed (p = .09). To further examine differences, Suffolk and Texel lambs (n = 5/breed) were infected with 10,000 Hc L3 for 30 days. Suffolk sheep had greater egg release per worm than Texel (3.8 vs. 2.1 eggs/worm). Taken together, these data would indicate one of the mechanisms in Texel's targeting adult-stage Hc reducing worm fecundity.