Traditionally in Ireland, dairy cattle have been vaccinated for leptospirosis just prior to breeding to prevent infertility. However, by this time in their life, they may already be infected. Seroconversion has been noted in younger animals, and we know that infected cattle can continue to shed leptospires in their urine.
L hardjo maternal antibodies decline to zero at around 13 weeks of age. This creates a ‘protection gap’, placing calves at risk of L hardjo infection- even in situations where calves are not reared close to adult cows. It is important to remember that L hardjo can survive for up to six months in wet conditions.
Currently there are no available data to show that vaccines can clear infection in already infected animals i.e. vaccines have not been shown to have any therapeutic effect. However, if young cattle are vaccinated before they become infected, this will prevent them becoming carriers. Routine “early calf” vaccination is a logical and practical way to prevent new carriers developing in a herd and to optimise leptospirosis control.