Success of Tick Feeding on Calves Immunized with Amblyomma Americanum (Acari: Ixodidae) Extract1

Jersey and Hereford calves were immunized with 3 mg/kg and 18 mg/kg, respectively, of Amblyomma americanum extract. Significant reductions in female engorgement weights were observed in ticks fed on immunized animals. Further reductions in both numbers and weights of egg masses and in rates of larval eclosion were observed when ticks fed on immunized Hereford calves. No significant differences were detected in egg mass to engorgement weight ratios regardless of host treatment. Differences in skin responses between treated and control calves were evident. No circulating antibodies were demonstrated in the immunized calves by the passive hemagglutination test.