Effect of vaccination in the field with the Theileria annulata (Hisar) cell culture vaccine on young calves born during the winter season

The responses were monitored of young crossbred calves vaccinated against t ropical theileriosis during the winter against a field tick challenge in th e disease season. Thirty-eight calves below 2 months of age, born after the end of the disease season, were selected at an organized farm. Twenty-five animals were vaccinated with Theileria annulata (Hisar) cell culture vacci ne (developed at CCS HAU Hisar laboratory) after the end of the disease sea son and 13 calves were kept as non-vaccinated controls. These calves were o bserved for their susceptibility to theileriosis in the new disease season. There was an increase in antibody titre in 18 of the 25 vaccinated animals one month after vaccination. The antibody titre then declined gradually, b ut remained higher than those of the non-vaccinated animals at month 0. No fever or other clinical signs of tropical theileriosis were observed in any of the vaccinated animals. Nine out of 25 (36%) vaccinated calves showed o ccasional piroplasms (<0.5%) in blood smears. All the vaccinated animals wi thstood the field tick challenge. On the other hand, 9 of the 13 (69%) unva ccinated calves exhibited occasional piroplasms, and included three clinica l cases of tropical theileriosis. These observations suggest that young cro ssbred calves vaccinated with the T. annulata (Hisar) cell culture vaccine at the end of the disease season were relatively resistant during the next disease season.