For decades, Neospora caninum was considered one of the most important infectious causes of abortion in dairy cattle. Researchers invested heavily in efforts to understand the parasite, developed diagnostic tests and uncovered how it spreads through herds. Then, somewhere along the way, the conversation faded.
Neospora caninum is a protozoan parasite and a major cause of abortion in cattle. Unlike many reproductive diseases, Neospora can persist within a herd through congenital transmission, with infected cows passing the parasite to their daughters and subsequent generations. This allows infection to remain within dam-daughter families for years. The parasite can also spread when dogs, coyotes and other canids consume infected placentas or aborted fetuses and shed Neospora oocysts in their feces, which can contaminate cattle feed. The result is a disease that can be surprisingly difficult to see.
A 2025 University of Minnesota study found that only 29% of surveyed producers had heard of Neospora, and just 12% had discussed it with their veterinarian. At the same time, the researchers identified a communication gap between veterinarians and producers and found evidence of Neospora exposure on every farm included in the study. Overall cattle seroprevalence was 20.9%, with individual herd prevalence ranging from 0% to 51.3%.
For Dr. Mark Thurmond, professor emeritus at the University of California, Davis, the findings were both familiar and frustrating.
“I thought everybody got the word that this is something that needed to be fixed. But I think it must have skipped a generation or something,” he says.
Thurmond was among the researchers who helped establish Neospora caninum as a major cause of bovine abortion in the 1990s. Today, he worries much of that knowledge has faded from everyday veterinary practice, even though the disease continues to affect herd health and profitability.
The Economic Cost of Neospora in Cattle
The apparent decline in awareness stands in contrast to the parasite’s estimated economic impact. A recent global analysis by Riechel and colleagues estimated annual losses approaching $1.3 billion across the dairy and beef industries, including approximately $546 million annually in the U.S. dairy industry and $111 million in the U.S. beef industry. Thurmond pencils out a cost from abortion and milk loss to a 1,000-cow herd with only a 40% prevalence to be $200,000 to $250,000 annually.
Thurmond believes the disease deserves renewed attention because its effects extend beyond abortion. Research has associated Neospora infection with reduced milk production, increased culling risk and reduced weight gain and feed efficiency in beef cattle.
Based on decades of research and field experience, Thurmond believes the more important question is not whether Neospora exists within the industry, but how much impact it is having on individual herds.
“Every dairy herd has Neospora. Without question, some as high as 60% to 80%. The question is how much they have and how much impact does it have,” he explains.
While prevalence varies considerably among herds, the Minnesota study reinforces that exposure remains common, with infected cattle identified on many participating operations.
Why Neospora Can Be Difficult to Recognize
Part of the challenge, Thurmond says, is that the disease is insidious and does not reveal itself with any obvious signs. Consequently, diagnosing Neospora as a cause of fetal loss requires what is called a case-control assessment, whereby aborted and non-aborted cows are tested and the odds of being positive are compared for the two groups. Odds ratios greater than 1.0 mean there is a real impact of Neospora on the herd; the greater the ratio, the greater the impact.
Research conducted by Thurmond and colleagues in the 1990s demonstrated that congenital transmission from dam to daughter is the primary mechanism by which Neospora persists within dairy herds, where an infected cow can be expected to transmit Neospora to every one of its fetuses 100% of the time. Rather than causing dramatic abortion storms, the disease typically results in early fetal loss that can be mistaken for poor reproductive performance.
“What I found was that Neospora is silent. You’re not seeing an abortion storm. You’re just saying, ‘Oh, geez, we can’t get these cows pregnant. We can’t get them to stick,’” recalls Thurmond.
This distinction may help explain why the disease has gradually slipped out of routine conversation despite decades of research documenting its impact.
New Reproductive Tools Could Change Neospora Control
Thurmond believes the industry now has control tools that didn’t exist when Neospora first emerged as a major research priority.
For many years, controlling the disease largely meant culling infected cows, an approach that was financially unrealistic for herds with high prevalence. Today, however, widespread use of sexed semen, beef-on-dairy breeding programs and embryo transfer provides opportunities to gradually reduce the number of infected replacement females while maintaining herd productivity.
“Thirty years ago, the option you had was really one: cull. But nowadays the horizon really opened up. Now we’ve got male and female semen. And we’ve got this crazy market for beef-on-dairy,” he says.
Rather than attempting to eliminate infected animals all at once, Thurmond proposes gradually breeding Neospora out of a herd over multiple generations. His recommendations include:
- Identify infected animals through strategic serologic testing to estimate the impact of the disease and identify infected dam families.
- Prioritize Neospora-negative females as herd replacements while incorporating infection status into culling decisions.
- Breed infected cows to beef sires using male-sexed semen, producing valuable beef-on-dairy calves while limiting the number of infected replacement heifers entering the herd.
- Breed uninfected cows and heifers with female-sexed dairy semen to expand the pool of Neospora-negative replacements.
- Strengthen biosecurity by preventing feed contamination with dog or coyote feces and removing placentas and aborted fetuses before they can be consumed by canids.
This management strategy builds on decades of published research, while taking advantage of reproductive technologies that were unavailable when Neospora first emerged as a major reproductive disease.
Farm Biosecurity Can Prevent New Neospora Infections
While reproductive technologies can help reduce the impact of congenital transmission over time by strategically removing infected cows, biosecurity remains critical for preventing new infections from entering a herd.
Dogs, coyotes and other canids become infected after consuming infected placentas, aborted fetuses or other tissues. Once infected, they can shed Neospora oocysts in their feces, potentially contaminating feed or feed storage areas. Research by Thurmond and Hietala found that on well-managed dairies, postnatal transmission through contaminated feed likely accounts for only a very small proportion of new infections, with congenital transmission remaining the primary mechanism maintaining infection within a herd. Even so, contamination of feed by infected canids can still trigger abortion outbreaks in previously uninfected cattle.
To reduce the risk of postnatal transmission, Thurmond recommends the cattle community:
- Keep dogs and coyotes out of commodity sheds, feed bunks and feed storage areas.
- Promptly remove and properly dispose of placentas and aborted fetuses so they cannot be consumed by dogs or wildlife.
- Regularly inspect feed storage and feeding areas for fecal contamination and clean contaminated areas before feed is distributed.
- Control rodent populations, which can also serve as intermediate hosts and contribute to the parasite’s life cycle.
Why We Need to Revisit Neospora
No effective Neospora vaccine has been developed, and controlling the disease still requires careful testing, biosecurity and long-term decision making. Yet the combination of renewed research, evolving reproductive technologies and persistent economic losses raises an important question: Has the industry stopped thinking about a disease that still deserves attention?
Perhaps the timing is more than coincidental. Just as awareness of Neospora appears to have faded, the industry’s reproductive toolbox has expanded, making long-term control strategies far more feasible than they were three decades ago.
For Thurmond, that’s exactly why the conversation needs to start again:
“It’s a national problem for the dairy industry. It’s really holding the dairy industry back. We need to take a closer look.”
