Influence of host genetics upon antibody responses against gastrointestinal nematode infections in cattle.

Previous studies have shown that the number of gastrointestinal nematode eggs released per gram of feces (EPG) of calves is strongly influenced by host genetics. The purpose of this study was to determine if host genetics also influenced immune recognition of parasite antigens in these same calves. Serum samples were taken at monthly intervals from calves during their first grazing season, from approximately 4 months after the onset of calving and were continued until weaning. Serum samples were analyzed for antibodies against Ostertagia ostertagi, Haemonchus placei, Cooperia oncophora, and Oesophagostomum radiatum. Significant rises in antibodies of the IgG1 class were seen against Ostertagia ostertagi, H. placei, and C. oncophora. In addition, rises in anti-Ostertagia antibodies of the IgG2 and IgM isotypes were also noted. During periods of elevated antibody responses, the sire of the individual calves was found to influence significantly the level of circulating antibody. The heritability of serum anti-parasite antibody levels was demonstrated to be between 70 and 80%, depending upon the time and antibody isotype. The antibody levels did not appear to be correlated with parasite EPG values. These results indicate that the ability of calves to recognize parasite antigens is strongly influenced by genetic factors, and that the genetic factors which control antibody responses may differ from those controlling EPG values.