Neosporosis: A Commonly Missed Cause of Abortions Also Leads to Reduced Weight Gain in Feeder Cattle

by Jill J. Dunkel

Neosporosis is a relatively new disease that can cause abortions and stillbirths in cattle. Although many producers vaccinate for abortion-related ailments such as leptosporosis and vibriosis, neosporosis is not commonly vaccinated against.

However, in California state diagnostic laboratories, neosporosis was the leading cause of abortion in cows, more than all other pathogens combined.

Neosporosis is caused by the parasite Neospora caninum. The disease is spread by dogs (the final host) that eat infected fetuses or afterbirths. The parasite infects tissue, then produces eggs (oocysts) in the dog's digestive tract, which is passed on through the feces. When cows graze near the contaminated feces, they can ingest the eggs, introducing the parasite into their system. Infected dogs defecating near feedstuffs or in water sources are the most likely sources of Neospora contamination of feeder cattle.

"Dogs were first identified as the host animal two years ago," according to Dr. Leszek Choromanski of Intervet. "Recent research in Texas has indirectly implicated coyotes and foxes as possible final hosts as well. Whether other carnivores can excrete or produce Neospora eggs needs to be investigated."

According to Dr. Choromanski, there are no clinical symptoms of a Neospora infection. A producer typically suspects a problem if he sees a cow that has recently aborted or finds a large number of open cows in his herd. Diagnosis is made by testing blood samples and/or aborted fetuses. "Ask to run an abortion panel, including Neospora," Dr. Choromanski says. "Some labs don't traditionally include Neospora in their lab work. It is common to miss."

Although Neospora has only been identified for 13 years, the costs associated with the disease are phenomenal. Neosporosis could cost Texas beef producers more than $37 million in 2001, according to research by Dr. Kerry Barling of Texas A&M University.

"The potential loss to the Texas cow-calf industry because of abortions, still births and increased culling is estimated at $24 million each year," Barling says. "When we factor in Texas feedlots, we could possibly see another $13 million in losses."

In fact, among 1,000 beef calves evaluated in 1998 in the Texas Ranch to Rail program, 13 percent tested positive for carrying the Neospora caninum infection. "We just learned last November that a Neospora infection causes a 2.4 percent lower calving rate and a decrease in weight gain of about 2.3 percent, which equates to $17.71 per head in feeder cattle," Choromanski explains.

Additional Texas A&M studies are underway, with one project looking into Neospora's impact on feed efficiency.

"This is a significant problem in cattle country, yet it is unknown to most producers," says Barling. "More research is necessary to raise the awareness level."

A vaccine for Neospora caninum, developed by Dr. Choromanski and his research team, has been on the market since December 1998 and is manufactured by Intervet. "The vaccine is intended for reducing abortions," he says. Intervet recommends administering the Neospora vaccine during the first trimester (with the first dose at 45 days gestation, which is traditionally pregnancy checking-time for many producers.) A booster three to four weeks later is also needed, explains Dr. Choromanski.

At this time, the vaccine is not intended for use in feeder cattle because the majority of the research with the Neospora vaccine was directed at the reduction of abortion in pregnant cattle. Research in feeder cattle is underway.