Lepto in Cattle: Signs, Prevention, and Management

Leptospirosis is one of the most economically damaging infectious diseases in cattle worldwide, responsible for abortion storms, milk drop, infertility, and chronic kidney shedding that can quietly sustain infection across an entire herd for years. The disease is caused by spirochete bacteria in the genus Leptospira, with several serovars affecting cattle differently. What makes lepto especially frustrating is that many infected animals show no obvious illness at all, silently spreading the organism through urine while producers lose calves and milk income without a clear culprit.

How Cattle Become Infected

Leptospires thrive in warm, moist environments. Cattle typically pick up the bacteria through mucous membranes or broken skin after contact with contaminated water, wet pasture, or urine from infected animals. The organism can survive for weeks in stagnant water or waterlogged soil, which is why outbreaks often cluster around wet seasons. Research in New Zealand found that cattle leptospirosis was positively associated with surface runoff and soil moisture, reinforcing that standing water and saturated ground are key risk factors on farms.¹

Wildlife reservoirs play an underappreciated role. Rodents, possums, deer, and feral pigs can carry and shed leptospires without showing disease. A cross-sectional study in New Zealand demonstrated that livestock are exposed to serovars circulating in wildlife sharing the same environment, with the serovar Ballum being a particular concern at the wildlife-livestock interface.² This means that even a well-managed, closed herd can become infected if wildlife access water sources or feed areas.

Different serovars have different maintenance hosts. Serovar Hardjo is considered “cattle-adapted,” meaning cattle themselves are the primary reservoir and can shed the organism for months or years through urine. Serovars like Pomona and Grippotyphosa are more commonly maintained by wildlife, and cattle are incidental hosts. The distinction matters because cattle-adapted serovars tend to cause chronic, subtle disease, while incidental serovars more often cause acute illness with dramatic symptoms.

Clinical Signs to Watch For

The signs of leptospirosis in cattle range from virtually invisible to devastatingly obvious, depending on the serovar involved, the animal’s immune status, and whether the infection is acute or chronic. Acute infections with non-adapted serovars like Pomona can cause fever, blood in the urine, jaundice, and a sudden drop in milk production in dairy cows. Calves and young stock are more vulnerable to severe acute disease than adults.

Chronic infection with cattle-adapted serovars like Hardjo is far sneakier. The most common presentation is reproductive failure: late-term abortions, stillbirths, the birth of weak calves, and reduced conception rates. A producer may notice a slow decline in herd fertility without any sick animals. In dairy herds, a sudden drop in milk yield across multiple cows, sometimes called “milk drop syndrome,” can be the only visible sign. The kidneys become colonized, and the animal sheds leptospires in urine for months, spreading infection to herdmates and anyone handling the cattle.

Abortion Storms and Fetal Loss

When leptospirosis first enters a naïve herd, the results can be dramatic. In one well-documented case in Saskatchewan, abortions occurred in 18% of a 131-head beef cow herd over just two months after infection with serovar Pomona. The diagnosis was confirmed by serology in the cows and by finding leptospires in fetal tissues. The abortion storm only stopped after vaccination against Pomona combined with oxytetracycline treatment of pregnant cows, though some animals developed chronic debility afterward.³

A large-scale study in New Zealand quantified the contribution of various pathogens to fetal loss in beef cattle. Animals seropositive to Hardjo had roughly twice the odds of fetal loss compared to seronegative animals, and unvaccinated cows exposed to Pomona had dramatically higher odds still. Overall, the researchers estimated that about 8% of all fetal loss in the New Zealand beef breeding population could be attributed to Hardjo and Pomona combined.⁴ That may sound modest, but across a national herd it translates to thousands of lost calves each year.

The timing of abortion is worth noting. Leptospiral abortions typically occur in the last trimester of pregnancy, often weeks after the initial infection when the cow herself may appear healthy. This delay makes it easy to miss the connection between an exposure event and the resulting losses.

Diagnosing Leptospirosis

Diagnosis is one of the trickiest parts of managing lepto in cattle, because no single test gives a complete picture. The traditional workhorse is the microscopic agglutination test, which detects antibodies in blood and identifies which serovars an animal has been exposed to. It is widely available and relatively inexpensive, but it has real limitations. A positive result tells you the animal has been exposed at some point; it does not necessarily mean the animal is currently infected or shedding. And in vaccinated herds, the serological response after vaccination is difficult to distinguish from the response after natural infection.⁵

Molecular testing using PCR has become an increasingly valuable complement. A study comparing PCR to traditional culture found PCR to be 100% sensitive and 99% specific for detecting Leptospira compared to the gold-standard culture method, with excellent agreement between the two techniques.⁶ PCR detects the organism’s DNA directly, so it can confirm active infection rather than just past exposure. The catch is that PCR works best on urine or tissue samples, and the timing matters: an animal may test PCR-negative in blood but still be shedding in urine.

More recent work comparing multiple diagnostic methods found that about 53% of cattle sera tested positive exclusively by serology, indicating past exposure, while only about 1% tested positive by molecular techniques alone, suggesting early active infection.⁷ The practical takeaway is that serology casts a wide net for exposure history, while molecular tests are better at catching animals that are actively infected right now. Using both together gives the most complete picture of what is happening in a herd.

Bulk Milk Testing for Dairy Herds

For dairy operations, testing bulk tank milk offers a cost-effective way to monitor herd exposure without bleeding individual animals. Antibodies from infected cows end up in the pooled milk, and a single sample can flag whether the herd has a leptospirosis problem. A study of over 300 unvaccinated dairy herds in Poland found a herd-level seroprevalence of about 3% for Hardjo using bulk milk testing, with the highest rates in medium-to-large herds of 50 to 500 animals.⁸

Researchers have also developed statistical models to estimate the proportion of exposed animals in a herd based on the bulk milk result. Work using data from Scottish dairy herds found strong evidence supporting the validity of interpreting bulk milk samples as a proxy for individual animal serum testing. By setting an appropriate cutoff, a single bulk milk test can provide high confidence that fewer than 5% of cows in the herd are exposed.⁹ For dairy producers, this means regular bulk milk screening can serve as an early warning system and reduce the need for expensive individual blood tests.

Treatment With Antibiotics

Once leptospirosis is confirmed, the primary goal of antibiotic treatment is to eliminate the organism from the kidneys and stop urinary shedding, which is the main route of transmission within a herd. Several antibiotics have proven effective. A controlled trial evaluating multiple options found that the following treatments all eliminated urinary shedding: a single injection of long-acting oxytetracycline, a single injection of tilmicosin, a single injection of a dihydrostreptomycin-penicillin combination, or a multi-day course of ceftiofur.¹⁰

In practice, oxytetracycline is the most commonly used option for whole-herd treatment because it is widely available, relatively affordable, and can be given as a single dose. During an active outbreak with abortions, treating all pregnant cows with oxytetracycline while simultaneously vaccinating the herd is the standard emergency response. As seen in the Saskatchewan outbreak described earlier, this combination stopped the abortion storm.³ However, antibiotics alone are not a long-term solution. They clear the current infection but do not prevent reinfection, so vaccination needs to follow treatment.

Vaccination and Long-Term Prevention

Vaccination is the backbone of leptospirosis control in cattle. Most commercially available vaccines are multivalent, covering several serovars including Hardjo, Pomona, Grippotyphosa, Icterohaemorrhagiae, and sometimes Canicola. The vaccines are killed (inactivated) products that require an initial two-dose series followed by annual boosters. Protection is serovar-specific, meaning the vaccine only covers the serovars it contains.

Experimental challenge studies have shown that vaccination can fully protect cattle from kidney colonization and urinary shedding. In one study, all vaccinated cattle were protected from colonization and shedding of Leptospira borgpetersenii serovar Hardjo following experimental challenge, as confirmed by culture and immunofluorescence.¹¹ A meta-analysis of vaccination trial data estimated a pooled vaccine efficacy of about 82% for preventing shedding.¹²

Timing matters. Heifers and bulls should receive their initial two-dose series well before breeding, because leptospirosis has the greatest reproductive impact during pregnancy. Annual boosters are typically given before the start of mating season. In endemic areas with year-round calving, some producers vaccinate every six months for tighter protection, though this adds cost. Calves born to vaccinated dams carry maternal antibodies that can interfere with early vaccination, so the first dose is usually delayed until about four to six months of age.

Beyond vaccination, biosecurity plays a supporting role. Fencing cattle away from stagnant water, controlling rodent populations around feed storage, and avoiding co-grazing with potentially infected wildlife all reduce exposure. None of these measures alone is sufficient, but they complement vaccination, especially against serovars not covered by available products.

The Semen and Bull Problem

One transmission route that is easy to overlook is through breeding bulls. Infected bulls shed leptospires in urine, and recent research has confirmed that semen can also carry viable organisms. A study testing frozen semen samples found that about 1.5% were positive for Leptospira DNA, and one of those samples yielded a live culture. The infectivity of the semen isolate was confirmed in an animal model, making this the first demonstrated case of viable serovar Hardjo being cultured directly from frozen semen.¹³

For producers using artificial insemination, this finding is concerning. Antibiotics are routinely added to semen extenders, but they may not fully eliminate leptospires, particularly in frozen straws. For natural service herds, an infected bull can spread the organism both through direct contact and through contaminated urine on pasture. The practical implication is that bulls should be included in herd vaccination programs and, ideally, tested before introduction to a new herd.

How Much Lepto Costs

Putting a dollar figure on leptospirosis is difficult because so much of the damage is subclinical: slightly lower conception rates, a few extra open cows, modest drops in daily milk yield that are easy to attribute to other causes. One study that tracked economic losses in a naturally infected commercial dairy herd before and after disease control found losses of up to 84% of the gross margin per liter of milk sold during the outbreak period compared to the controlled period.¹⁴ That is a staggering figure, driven by the combined effect of reduced milk production, abortions, infertility, veterinary costs, and culling of chronically affected animals.

In beef herds, the math centers on calf crop. When 18% of a cow herd aborts in a single season, as happened in the Saskatchewan case, the lost revenue is obvious. But even in herds where leptospirosis simmers at low levels, a few percent reduction in weaning rate year after year adds up. The cost of annual vaccination for a cow-calf herd is minimal compared to the value of even one or two extra calves saved.

Serovar Prevalence Varies by Region and Herd Type

Which serovars dominate depends on geography, wildlife populations, and whether the herd is beef or dairy. A large survey of Ontario cattle herds found that 39% of herds showed evidence of infection with at least one serovar. Pomona was the most commonly detected at a herd-level seroprevalence of about 26%, followed by Hardjo at about 14%. Interestingly, beef herds were far more likely to test positive for Hardjo than dairy herds: about 44% of beef herds compared to about 8% of dairy herds.¹⁵ The difference likely reflects management factors: beef cattle on range have more exposure to contaminated water and wildlife, while dairy cattle in confinement may have less environmental contact but more cow-to-cow transmission.

In other parts of the world, the serovar landscape can look completely different. In New Zealand, Hardjo and Pomona have historically been the main concerns in cattle, but an emerging serovar called Tarassovi has been increasingly detected in dairy workers. Because Tarassovi is not included in current cattle vaccines, it represents a gap in protection that matters for both animal and human health.¹⁶

The Human Health Connection

Leptospirosis is zoonotic. Dairy farmers, veterinarians, and abattoir workers are at highest risk because they have regular contact with cattle urine, reproductive fluids, and contaminated environments. In humans, the disease ranges from a mild flu-like illness to severe kidney and liver failure. A serological survey of New Zealand farmers found that about 7% were seropositive to at least one Leptospira serovar, with dairy workers particularly at risk.¹²

A case-control study of dairy farms found that the seroprevalence of Hardjo in cattle on farms where milkers had high antibody titers was significantly greater than on farms where milkers were seronegative. The researchers concluded that conventional protective measures for milkers, such as wearing gloves and avoiding splashback, appeared to be ineffective, and that preventing human leptospirosis in dairy workers could only be reliably achieved by eliminating infection in the herd through cattle vaccination.¹⁷ That is an important finding: protecting the people starts with protecting the cows.

The zoonotic risk extends beyond traditional farming settings. In low-income countries, urban and peri-urban dairy farming creates environments where large numbers of humans and animals coexist in close quarters, amplifying the risk of transmission. Research has highlighted dairy cows in these settings as commonly exposed to Hardjo, posing a public health risk that often goes unrecognized by urban health authorities.¹⁸

Weather, Water, and Outbreak Timing

Producers in wet climates or flood-prone regions deal with lepto more than those in arid areas, for straightforward reasons. Leptospires cannot survive drying or direct sunlight, but they persist for weeks in water and moist soil. The New Zealand study on rainfall and leptospirosis found a statistically significant link between surface runoff, soil moisture, and cattle leptospirosis cases. Mean rainfall and extreme rainfall events showed a positive association as well, though the confidence intervals for those variables were wider.¹

Seasonality varies by region. In temperate climates, outbreaks peak in late summer and autumn when warm, wet conditions are optimal for bacterial survival and cattle are more likely to congregate around diminishing water sources. In tropical regions, the rainy season is the high-risk period. Producers can use this knowledge to time vaccination boosters before the expected peak, and to be especially vigilant about water management during wet months. Draining low-lying areas, maintaining clean water troughs, and limiting access to ponds or streams where wildlife may have urinated are all simple steps that reduce, though never eliminate, the environmental bacterial load.

When Lepto Looks Like Something Else

One reason leptospirosis goes undiagnosed is that its signs overlap with several other common cattle diseases. Late-term abortions can be caused by bovine viral diarrhea, neosporosis, brucellosis, trichomoniasis, and a long list of other infectious agents. Milk drop in dairy cows can be triggered by mastitis, heat stress, or nutritional problems. The New Zealand fetal loss study found that Leptospira, Neospora caninum, and bovine viral diarrhea virus collectively accounted for about 14% of all fetal loss in beef breeding cattle, with each pathogen contributing a similar share.⁴ Because no single pathogen dominates, a thorough diagnostic workup is essential when reproductive losses spike. Submitting aborted fetuses and placentas for laboratory testing, paired serology on aborting and non-aborting cows, and urine PCR on suspect animals all help narrow the cause.

Veterinarians familiar with lepto know to keep it on the differential list even when initial signs point elsewhere. The classic mistake is attributing poor conception rates to bull fertility problems or nutritional deficiency when a low-grade Hardjo infection is the real driver. If reproductive performance does not improve after addressing the obvious management factors, a leptospirosis investigation is warranted.