Is Leptospirosis Lurking?
Cow-calf profits depend largely on reproduction, with relatively small reductions or gains in calving rates having significant impact on annual returns. And while reproductive diseases such as leptospirosis can play a role, a broad approach toward addressing infertility can provide lasting benefits.
“If I’m investigating herd infertility, I’m not immediately thinking of leptospirosis,” says W. Mark Hilton, DVM, technical consultant with Elanco technical services. Reproductive problems, he says, typically are multifactorial and might be difficult to diagnose, but the causes usually involve non-disease issues such as bull fertility, cow nutrition, genetics, toxins or others.
“If pregnancy rates in a herd usually run 90% and drop to 84% at pregnancy check, we’ll take a close look at those non-disease factors before testing for lepto,” Hilton says. He adds this evaluation should include the producer, veterinarian and nutritionist if possible, covering the entire management system and looking for changes that might have affected fertility. Leptospirosis certainly is a potential cause of abortions, weak calves and open cows, but probably not as common as many producers believe.
Leptospirosis in cattle, which is generally caused by one of two types of the Leptospira hardjo bacteria—Leptospira hardjo-bovis or Leptospira hardjo-prajitno, can be difficult to diagnose. These bacteria infect the kidney and genital tract of cattle and are associated with abortions at all stages of gestation including early embryonic death. More than half of the abortions associated with leptospirosis occur during the third trimester.
“Cases of leptospirosis in cattle have declined. However, submit samples from multiple abortions if possible because it sometimes takes several to find a positive result.”
—Dan Grooms, DVM, Ph.D., Michigan State University
Michigan State University veterinarians Dan Grooms, DVM, Ph.D., says limited studies in the U.S. estimate herd prevalence of the serovar Hardjo strain to be near 60% in dairies and 40% in beef herds. Multiple diagnostic lab surveys have found Leptospira associated with less than 10% of aborted fetuses. Because of the overall difficulty in making a definitive diagnosis in bovine abortions, he adds, it is likely these surveys underestimate the true prevalence of Leptospira-related abortions.
Animals can be divided into maintenance hosts and incidental hosts of Leptospira, Grooms says. In a maintenance host such as cattle, the disease is maintained by chronic infection of the renal tubules.
Transmission of the infection among maintenance hosts is efficient and the incidence of infection is relatively high at a population or herd level. Incidental hosts might become infected by direct or indirect contact with the maintenance host, and are not important reservoirs of infection and the rate of transmission is low. Dogs, raccoons, skunks and other mammals serve as maintenance hosts and can introduce leptospirosis to herds.
Vickie Cooper, DVM, Ph.D., at the Iowa State University diagnostics laboratory, says leptospirosis is on the standard list of tests for diagnosing bovine abortions at ISU and other diagnostic labs.
However, Cooper says, most herds are well-vaccinated against leptospirosis, and she does not see many acute cases in cows. But while it does turn up in some herds where abortions or conception problems appear, some producers retain a bias, suspecting lepto when other problems are more likely.
Hilton stresses herd history plays a role in diagnosing fertility problems. Any sudden decline in pregnancy or calving rates deserves close attention, and if previous testing has confirmed lepto in the herd, testing is justified. However, some producers can assume they have a lepto problem and focus on that while not addressing more common problems. They might, for example, blame their vaccination program and switch vaccines, then see the same problem the following year.
Continue reading the second part of this article: Challenges of Getting A Lepto Diagnosis
