BREED DIFFERENCE IN ACQUIRED-RESISTANCE OF SHEEP TO HAEMONCHUS-CONTORTUS

Parasitological, pathophysiological and immunological parameters were compared between a-year-old domestic Nali and Merino crossbred sheep e xperimentally infected with Haemonchus contortus. The natural gastroin testinal nematode infection acquired during the previous grazing seaso n over a period of 6 months on pasture was terminated by anthelmintic treatment and both the breeds were then reinfected experimentally with H. contortus. No significant differences were found between the breed s in egg count and worm burden except that Nali sheep shed significant ly fewer eggs on day 27 following reinfection. Likewise, no significan t differences in the value of haemoglobin, packed-cell volume, total s erum proteins, calcium and phosphorus levels were noticed between the 2 breeds, nor any difference detected as regards the gamma globulin le vels, skin thickness and cellular response at the local sites and abom asal mucosa.