Vaccination of healthy calves over 4 months of age usually results in immunity. Because of the likelihood of some calves becoming infected before reaching 4 months of age, calves should be vaccinated when about 1 month old and re-vaccinated at 4 to 6 months. Cows should be vaccinated annually, before calving, with a multivalent clostridial bacterin to maintain continued protection. It is one of the leading causes of abortion, infertility, stillbirth and weak calves. Clinical signs of leptospirosis include fever, bloody or thick yellowish milk, decreased milk production, port wine-colored urine, anemia and jaundice.
Death is rare in adults, but frequent in calves.
The kidneys are a target organ when an animal has leptospirosis and affected animals shed organisms in their urine for varying periods of time. Recovered and apparently healthy cattle may excrete leptospires in urine for several months, serving as a source of infection for other animals in the herd. There are six known strains of lepto organisms that infect cattle. The most common strain, L. pomona, is readily transmitted between many animal species. On the other hand, L. hardjo is strictly a disease of cattle and is spread only within that species.