The first sign of a chronic infection is an abortion. Treatment after an abortion is too late. Prevention through regular herd vaccination is the best approach. The entire breeding herd should be vaccinated at least once a year. Be sure to vaccinate bulls and replacement heifers as well as mature brood cows.
Most cattlemen handle animals in the breeding herd at least twice a year anyway.
Most lepto vaccines are safe to use in pregnant cattle, making it possible to vaccinate during pregnancy checking. The two vaccinations should be administered about 6 months apart. However, the main consideration is to vaccinate twice a year, even if the time between them is more or less than 6 months. Replacement heifers and newly introduced young bulls should be vaccinated twice, about 3 to 4 weeks apart, as soon as possible after entering the herd. Like children, young animals require initial vaccinations followed by boosters.