Watching for neosporosis

Cow-calf producers considering raising dairy-cross calves—or beef-on-dairy calves—for replacements should be aware of neosporosis, a disease that can significantly impact bovine reproduction. Caused by infection with Neospora caninum , a protozoal parasite, neosporosis was first recognized in 1984—and by 1988 had emerged as a disease of concern within the dairy industry.

Cows acquire N. caninum in one of two ways: 1) “vertical” transmission of the organism from cow to fetus during pregnancy, or 2) “horizontally” by consuming feed or water contaminated with the parasite’s eggs (oocysts)—which is considered rare.

But it all starts with dogs and their wild cousins, which are definitive hosts for Neospora . After a dog eats infected placenta or aborted fetuses, oocysts are shed in their feces, which, when consumed by cows, continues infection with the parasite.

Dairy farms operate in an environment conducive to acquiring infection from feedstuffs contaminated with heavy loads of dog feces—which may or may not be similar to beef operations.

Cows pass the Neospora parasite to their daughters, that pass it on to their daughters, without interruption at nearly a 100% transmission rate. A distinguishing feature of the disease is abortion at 3-6 months of gestation. Because it’s a very efficiently transmitted parasite, infection rates can reach up to 90% in dairy herds.

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“This organism is still out, there and it’s still causing abortion problems in dairy cattle,” said Dr. Mark Thurmond, DVM, a retired veterinary researcher from the University of California, Davis. “And the beef industry should be warned of the situation.”

Building beef herds

Limited studies in beef herds show much less Neospora prevalence than in dairy herds. But a survey published in 2001 showed that in 55 beef herds in five states (Idaho, Montana, Oregon, Washington and Wyoming), prevalence of N. caninum was 23%.

Today, as cow-calf producers scramble to build their herds and scrape together female replacements, they may be tempted to turn to dairy-cross cattle. Even when using sexed semen for artificial breeding, Thurmond said it’s inevitable that some beef-on-dairy offspring will enter the nation’s cowherd.

By using those dairy-cross heifers, cow-calf operators could be “seeding” their herds with the Neospora organism.

“The practice of seeding beef herds with this parasite will render every female born to those infected replacements more likely to abort compared with an uninfected female,” Thurmond explained. “Daughters of an infected cow will be infected.”

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A similar problem may be occurring in embryo transfer situations where embryos are transferred to Neospora- infected recipients. Thurmond said this guarantees that any female offspring will experience a higher risk of abortion and will pass that risk on to their female offspring.

While it’s a rarer path of Neospora transmission, cow-calf producers who winter cows or heifers in a feedlot setting could be setting their herds up for exposure to N. caninum through feed contaminated with canine feces. Thurmond advises ranchers to watch for dog “toilet” areas where feces can build to appreciable amounts. Also, producers should try to prevent dogs from eating placentas or aborted fetuses.

Screening for neospora

Because there is no effective vaccine or treatment for neosporosis, the disease can only be avoided by serologic testing females for Neospora . Along with sending any aborted tissue to a diagnostic lab for testing, Thurmond advises cattle producers to work with their veterinarians and routinely screen cows for N. caninum antibodies.

He said heifers should be at least six months old when tested to ensure that any colostral antibodies to Neospora have decayed to undetectable levels—minimizing the possibility of false-positive tests.

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“I’d like to see some data on the percent of beef-on-dairy heifers one might expect to be seropositive to Neospora ,” Thurmond added. “I really feel that at some point someone will need to do this.”