No doubt you've heard of an abortion storm that swept through a herd, leaving a path of destruction in its wake. Or, maybe that herd just so happened to be yours. Whether or not the event took place on your dairy or someone else's, you quickly learn that neosporosis is to blame.

Maybe you don't know a lot about neosporosis, other than the fact that it causes abortions. However, neosporosis - an infection caused by a protozoan parasite known as Neospora caninum - is a widespread problem.

In fact, the problem extends beyond California - a state traditionally pegged as a hotbed for the infection.

A survey of 40 dairy herds across the Midwest revealed that more than 80 percent of those herds had at least one animal test positive for neosporosis, says Dan Weinstock, veterinarian with the Pennsylvania Animal Diagnostic Laboratory at Penn State University. "We found it pretty much everywhere we looked," he adds.

That means all producers need to be aware of the destructive capabilities of neosporosis. Use the answers to these five questions to gain a better understanding of neosporosis and how to manage it on your dairy.

Question: How do I control the spread of neosporosis on my dairy?

Answer: To successfully control neosporosis, you must interrupt the cycle of vertical transmission from cow to calf and horizontal transmission from dog to cow, says Weinstock.

Two strategies exist to help you minimize infection by dogs or other host animals:

  • Dispose of aborted fetuses, placenta and fetal membranes and do not allow dogs, cats or wildlife to have access to them.
  • Protect feedstuffs from fecal contamination by dogs, cats and wild animals.

Three management strategies exist to help you reduce neosporosis transmission from cow to calf:
1. Cull infected animals.
2. Test young calves, and do not raise those that are infected.
3. Test herd additions to prevent the introduction of neospora-positive animals.

All producers should institute management practices to limit horizontal transmission, says Weinstock. However, "the decision to limit vertical transmission depends on individual herd economics."

Question: I've heard dogs spread neosporosis. Does that mean I should get rid of all dogs on the dairy?

Answer: Although dogs have been identified as the definitive host for neosporosis, it is not necessary to remove all dogs from the dairy.

"People tend to think in terms of the definitive host," says Mark Anderson, veterinarian with the California Animal Health and Food Safety Laboratory at the University of California-Davis. In fact, some producers are quick to blame dogs when a neospora outbreak occurs.

However, the majority of infections actually occur through vertical transmission when an infected cow passes neosporosis to her heifer calf, Anderson says. This calf continues the cycle of infection when she matures and becomes pregnant.

Furthermore, the dog serves as a poor host because it does not shed a whole lot of Neospora caninum oocysts, Anderson adds. That's not to say neosporosis won't occur through horizontal transmission when cows consume oocysts shed by an infected dog. It's just simply not as likely as transmission from an infected cow to her calf.

To learn more about each of these methods of transmission, please see "The path of infection," on page 36.

In fact, keeping a dog or two around may deter wild carnivores - another possible host for neosporosis - from approaching the dairy, Anderson adds.

Question: Does neosporosis reduce milk production?

Answer: Although abortion is the only clinical sign of neosporosis, it does not limit itself to hampering your cows' reproductive performance.

It also has been shown to reduce milk production an average of 2.5 to 3 pounds per cow per day.

A University of Florida study confirms this observation. The results, published in the Sept. 1, 2001 Journal of the American Veterinary Medical Association, show neospora-positive cows produced 2.8 pounds less milk per cow per day than negative cows.

Other studies, however, show conflicting results.
A Canadian study found that neospora-positive cows in herds with abortion problems produced about 607 pounds less milk during a 305-day lactation than negative cows. But in herds without abortion problems, neospora-positive cows actually produced about 332 pounds more milk during a 305-day lactation than negative cows, notes Jamie Hobson with the Ontario Veterinary College at the University of Guelph in Ontario, Canada. The researchers speculate the positive cows may have mounted an immune response to the infection, which may explain why they did not experience reduced milk production.

Question: What is the economic impact of neosporosis?

Answer: Abortions caused by neosporosis cause significant economic losses to producers. The cost of abortions and reduced milk yield really adds up.

In California alone, neosporosis accounts for about 40,000 abortions annually, according to estimates published in the April 15, 1999 Journal of the American Veterinary Medical Association. At a cost of $850 per abortion, that puts total losses in California close to $35 million.

And because neosporosis exists across the country, these losses certainly apply to producers in other states, also.

Economic losses associated with reduced milk production also steal profits.

The University of Florida study mentioned previously estimates a per-cow, per-day production loss of 2.5 to 2.8 pounds, which results in a loss of 762 to 854 pounds per cow during a 305-day lactation. At $10 milk, an 800-pound drop per cow amounts to a loss of $80 per cow during her lactation.

Neosporosis also increases the cost associated with rebreeding cows that aborted and the cost associated with replacing infected animals that were culled from the herd.

Question: What do we know about the new neospora vaccine?

Answer: In addition to the management strategies listed above, a vaccine is available to help control neosporosis. The vaccine is still new to the market, and at this point we do not have any peer-reviewed studies on the product.

However, several field trials have yielded positive results. As with any vaccination program, always discuss the pros and cons with your veterinarian to determine if a vaccination program is the right option for your dairy.

This is what field trials have shown so far:

  • A vaccine challenge trial was conducted on pregnant heifers in DeSoto, Kan. Of the 18 heifers that were vaccinated for neosporosis, none experienced abortions after being challenged with Neospora caninum. Four of the 18 non-vaccinated heifers experienced abortions as a result of neosporosis.
  • In a 107-cow herd in Minnesota, the vaccine reduced the number of abortions from 27 per year to four. Of those four, none were associated with Neospora caninum, says Les Choromanski, veterinarian and NeoGuard(tm) manager with Intervet.
  • A field trial, involving 757 cattle from seven commercial herds across the U.S., indicates the vaccine is safe for use in healthy, pregnant dairy cattle.

Remember, vaccination alone won't stop the threat of neosporosis. Management practices to control your cows' exposure to neosporosis are just as important as vaccination, adds Weinstock.

Ask your veterinarian

Your veterinarian learned all about neosporosis in a three-part series featured in the March-April, May-June and July-August issues of our sister publication, Bovine Veterinarian. Ask him about it.