An often-overlooked reason for late-term abortions in gestating beef cows and heifers is neosporosis, which is difficult to prevent. Gregg Hanzlicek, director of production animal field investigations for the Kansas State University Veterinary Diagnostic Laboratory, said the laboratory has confirmed a handful of cases this spring calving season in Kansas.
Neosporosis, Hanzlicek said, is caused by Neospora caninum, a coccidian parasite carried by dogs—wild and domestic. It was first discovered in the United States in 1988, but tests on stored older tissues have confirmed the organism’s presence since at least the 1950s.
“We talk a lot about it on the dairy side, but this organism is also present in beef cow-calf operations,” Hanzlicek said.
Dogs, coyotes, gray wolves and dingoes are the definitive hosts of neospora, and they become infected by eating bovine contaminated tissues such as muscle, placenta and aborted fetuses, Hanzlicek explained.
“(Neospora) goes into the intestine of these canines, undergoes some changes and then is shed in the feces,” he said. “It goes through another life cycle on the ground. The cow ingests the contaminated feces, or ingests water or feed that contains the contaminated feces. It then moves to multiple tissues in the bovine: for example, muscles, brain and neurologic tissues, and the liver.”
Hanzlicek said neospora does not transmit from bovine to bovine, just canine to bovine and back to canine. The main effect of a neospora infection is an abortion, which typically happens after three months of gestation. The most common time for abortion to occur is during the fifth or sixth month.
“Research shows (neospora) has no effect on pregnancies less than 90 days,” Hanzlicek said. “For a newly infected herd, a lot of times we’ll see an epidemic, an abortion storm.”
He defines an “abortion storm” as more than 10 percent of the animals abort within a month to five-week period. Herds that have been infected for a long time typically show no visible negative effects, other than possibly an abortion rate slightly higher than expected but not considered an abortion storm.
“Once this organism is in a pregnant animal, it gets into the placenta and causes a disruption of the oxygen transport system,” Hanzlicek said. “The fetus dies and is aborted. Sometimes the organism enters the placenta, and the cow herself will set up an inflammatory response that will abort the fetus. The other thing that can happen is the organism can enter the fetus and cause organ shutdown. The fetus dies, and again, we have an abortion.”
For those calves born to infected cows or heifers, but are not aborted, they have about a 90 percent likelihood of being born with the disease, he said. Most of these calves appear and act normally. The only time they might show problems is if they abort after becoming pregnant.
Once a cow is infected, she is persistently infected throughout life, but the risk of abortion tends to decrease as a cow ages, Hanzlicek said. “We think (the cows), through time, set up some type of an immunity that holds the organism in check.”
Tips for prevention
Hanzlicek said to help prevent the spread of neospora, keep dogs from eating aborted fetuses, placentas, or deceased cows or heifers that could be infected.
“A study completed some years ago indicated that a low percentage of domestic dogs in Kansas were carriers of this organism,” he said. “Understandably, contamination through coyotes may be more difficult to control than domestic canines.”
Cow-calf producers who don’t feed silage, ground hay or don’t feed in bunks are at a lesser risk, Hanzlicek said, because the likelihood of widespread feed or feeding-area fecal contamination is unlikely. But, producers still have the danger of feces contaminating a water source.
“This disease is difficult to prevent, and testing replacements before purchase may be warranted,” Hanzilcek added. “If your herd is experiencing an abortion issue, always call your local practitioner, and let them decide if neospora fits the pattern of abortion in your herd. If there is an abortion storm going on, sample the aborted fetus and placenta, and also take a blood sample from the dam.”