SERUM ANTI-TRICHOSTRONGYLE ANTIBODY-RESPONSES OF 1ST AND 2ND SEASON GRAZING CALVES

Serum anti-Ostertagia ostertagi and anti-Cooperia oncophora antibody r esponses were assessed in first season and second season calves grazin g permanent paddocks. Calves without previous exposure to trichostrong yles were found to mount significant parasite-specific IgG1 antibody r esponses within two months of introduction to the pastures. A signific ant serum IgA response to O ostertagi and IgG2 responses to both O ost ertagi and C oncophora antigens were also observed, but these response s were weaker. No consistent serum anti-trichostrongyle IgM responses were discernible in either age group. Second season grazing calves had significantly elevated IgG1, IgG2 and IgA antibody levels at turnout when compared to first season calves, but only IgA antibody levels aga inst O ostertagi increased during the second grazing season. Compariso n of serum antibody levels in first and second season calves grazed se parately or together suggests that mixed grazing had no discernible ef fect on antigen priming.