VARIATION IN IMMUNE RESPONSIVENESS OF SHEEP TO THE ANTIGENS OF INTESTINAL NEMATODES AND BLOWFLY LARVAE

The total and IgC(1) antibody responses to the intestinal nematode par asites Haemonchus contortus and Trichostrongylus colubriformis were me asured in the serum of 160 lambs, 4 months of age, These antibodies ha d developed as the result of natural exposure to the parasites on past ure. Three sires were examined and strong sire effects on half-sib pro geny were found. Plotting of ELISA antibody results in two dimensions revealed clustering of responses within sire groups. Bimodal antibody distributions were also observed within sire groups and the whole popu lation for T. colubriformis, A bimodal distribution of antibodies to H . contortus was found for one sire group but not for the whole populat ion. The injection of blowfly larvae (Lucilia cuprina) extract into 42 /160 lambs at a later age (12 months) was followed by increased antibo dies to L, cuprina and an apparent increase in antibodies to T. colubu iformis. A bimodal distribution for antibodies to L, cuprina was found in one sire group and in the !whole population. These bimodal distrib utions of antibodies to L. cuprina did not coincide with the distribut ion of antibodies to T. colubuiformis or H. contortus, measured on the same serum samples. It was concluded that high and low responder sire groups could be differentiated in lamb populations for all three para sites. These effects persisted during lamb maturation and appeared to be genetic effects. Finally, crossreacting antibodies between L. cupri na and T, colubriformis appear to be stimulated by injection of L. cup rina antigens.