Strangles in horse studs: incidence, risk factors and effect of vaccination.

A questionnaire survey of 179 horse studs in New South Wales was conducted to estimate the incidence of strangles during 1985 to 1988, to identify risk factors for strangles outbreaks and to assess the effect of strangles vaccination. Forty-nine of the studs (27.4%) had at least one strangles outbreak during this period and 62 studs (34.6%) had at least one case of strangles. The average incidence of strangles was 2.1 cases per 100 horses per year. The risk of strangles increased progressively with the total horse population and rose markedly when more than 100 mares had been served in the 1988-89 season. Certain types of feeders, fences and water sources were also significantly associated with outbreaks of strangles. Strangles vaccine was used on 63 studs (35.2%). Thirty-seven of these (58.7%) used the manufacturer's recommended vaccination regime. When other risk factors were taken into account, vaccination had no significant effect on the likelihood of a strangles outbreak.