While beef cattle veterinarians and re-searchers are just now getting acquainted with neosporosis, they understand the potential havoc it can create.
Neospora caninum-induced abortion and stillbirths will cost the beef cattle industry in Texas more than $37 million this year, estimates Kerry Barling, a Texas A&M University veterinary researcher.
The disease is spread primarily by dogs, but coyotes and foxes are also possible “definitive” hosts. Dogs consuming infected fetuses shed Neospora caninum eggs in their feces. The forages and feed contaminated by the feces are then ingested by cattle and the organism's life cycle continues.
Infected cows pass Neospora caninum through the placenta to the fetus. Neosporosis primarily affects the brain and nervous system of fetuses and newborn calves.
Transmission may result in aborted fetuses, infected calves or healthy calves. Abortions usually occur in the fifth or sixth month of gestation. A California study reported that more Neospora-induced abortions occurred in winter.
But, abortion is only part of the headache for beef producers. Barling recently published a study in the Journal of the American Veterinary Medical Association that indicates reductions in feed efficiency in feedlot cattle infected with Neospora caninum.
Barling's research shows the average daily gain (ADG) of Neospora-infected steers was .37 lbs. less than their non-infected buddies.
“The lower ADG wasn't due to the infected steers eating less,” says Les Choromanski, Neospora manager for Intervet Inc. He emphasizes that the organism did not significantly affect intake, but it suppressed feed conversion.
“The research shows that a neospora-positive steer required 2.16 lbs. of additional feed to increase live body weight by 1 lb.,” says Choromanski.
Neosporosis wasn't identified until 1988, and animal scientists are continuing to learn more about the disease. Neospora caninum is reported on virtually every continent and affects nearly every class of cattle. In Australia, neosporosis reportedly costs that beef industry $25 million/year.
It's estimated that neosporosis accounts for 40,000 abortions each year in California dairy cattle — or 42% of the state's dairy abortions, Choromanski says. The predicted economic loss to the Texas cow/calf segment may be as much as $24 million annually. The potential for feedlot losses in Texas is another $13-14 million each year, he says.
Among 1,000 beef calves evaluated in 1998 in the Texas Ranch-To-Rail program, 13% tested positive to carrying the Neospora caninum organism. The study reports that a 1,000-head beef herd with a 13% prevalence rate of Neospora infection could have an economic loss of $2,302 ($17.71/ head) because of an estimated 2.4% lower calving rate and an overall estimated 2.3% lower weaned calf crop.
Barling and other researchers are working to assess the impacts of neosporosis and its control. One tool now available to producers is NeoGuard™, an Intervet product granted approval as a vaccine in reducing abortions caused by Neospora caninum in cattle.
Choromanski recommends administering the vaccine to infected cows during the first trimester of pregnancy with a subcutaneous dose of 5 milliliters (ml.), followed by a second 5-ml. dose three to four weeks later. Revaccination with two doses is recommended for subsequent pregnancies.
