Application of an integrated outbreak management plan for the control of leptospirosis in dairy cattle herds.

Two outbreaks of Leptospira borgpetersenii serovar Hardjo infection in dairy cattle herds were managed through the application of enhanced biosecurity measures, whole-herd antibiotic treatment and vaccination. Micro-agglutination test antibody titres were determined in paired serum samples at 3 weeks (T1: n = 125, 97% seropositivity, median 800, range 100-12 800) and 24 weeks (T2: n = 110, 88% seropositivity, median 200, range 100-6400) after vaccination and studied in relation to cows' age, herd of origin and sampling time. From T1 to T2, vaccine-elicited antibody titres decreased by 84·7% (95% CI 76·2-90·1). Consistent with increasing immunocompetence in calves (aged <12 months) and immunosenescence in adult cows (aged >36 months) associated with ageing, antibody titres correlated positively with calves' age and negatively with adult cows' age. No cow had cultivable, (histo)pathologically detectable and/or PCR-detectable leptospires in urine or kidney samples after treatment and vaccination. Vaccination together with proper biosecurity measures and chemoprophylaxis are an affordable insurance to control bovine leptospirosis.