Leptospirosis in swine is not a clearly defined disease. Low level infections may be more widespread than recognized and may explain why breeding herds benefit from the feeding of Aureomycin® chlortetracycline at breeding and farrowing.

Ferguson et al. were the first to report that feeding diets containing 400 g/t CTC for 10 days to bred gilts (naturally infected with leptospirosis) had the effect of reducing antibody titers and kidney localization and also reduced the effects of the disease on the fetuses.

In similar research by Howarth, 200-lb hogs (naturally infected with leptospirosis) were treated with feed containing 400 g/t CTC for 14 days. At slaughter, leptospirae were isolated from the kidney tissue of 13 of the 23 non-medicated control hogs, but no organisms were present in the CTC-treated animals. Howarth further found that treating the breeding herd from which the infected hogs originated with 400 g/t CTC in the diet for 14 days was very effective in eliminating the L. pomona infection.

Leptospirosis is a reproductive disease of swine caused by Leptospira organisms, a certain type of gram-negative spirochete bacteria. These microbes invade the kidneys and urinary tract of pigs, so they are spread to other animals in the herd through urine and genital fluids, primarily by direct contact with the mucous membranes of the nose, mouth, and eyes, as well as in the vagina and milk.

Chronic leptospirosis causes most of the serious economic losses associated with the disease, triggering abortions, stillbirths, weak piglets, and even infertility. An acute phase of the disease causes infected pigs to consume less feed and become feverish and lethargic, but such mild signs often go unnoticed.

Leptospirosis, like most diseases, it is best controlled by prevention. Sanitation and other management practices that minimize the spread of leptospires from infected animals are of crucial importance. Therefore, antibiotics (like Aureomycin® and ChlorMax®) and vaccination can be very helpful for controlling leptospirosis, though vaccination provides only short-term protection against leptospire infection.