Abstract
The relationship between inoculation frequency and HI antibody titers in horses inoculated with equine influenza inactivated vaccine, and the distribution of HI antibody titers against 3 vaccine strains in racehorses, and rearing and breeding horses were surveyed. Two-year-old horses inoculated vaccine 3 times did not maintain antibody titer o132 for 5 months after the last injection. On the other hand, 3-year-old horses inoculated 4 times and 4-year-old horses inoculated 5 times sustained the titer for about 1 year after the last injection. Approximately 63% to 90% of 2-year-old horse group, 38% to 100% of 3-year-old horse group and 43% to 100% of horse group of more than 4-year-old at the Ritto and Miho training centers of the Japan Racing Association possessed titers of more than 32 against 3 vaccine strains. On the other hand, 0% to 22% of the 2-year-old horse group, 20% to 79% of the 3-year-oldhorse group, 36% to 86% of the 4-year-old horse group and 50% to 96% of the 5-year-old horse group at the Utsunomiya and Sonoda racecourses of the National Association of Racing possessed titers of more than 32 against 3 vaccine strains. Approximately 47% to 93% of rearing horses and 7% to 43% of breeding horses in the Hidaka region of Hokkaido possessed titers of more than 32 against 3 vaccine strains.
