AGRICULTURE

Neospora: An occasional and interesting cause of beef cow pregnancy loss

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Farm Forum

For cow-calf producers, finding a “slipped” or aborted calf in the cow yard usually is met by a pang of anxiety – and questions: How many more cows will abort? And, what’s causing it?

The list of potential causes of cattle abortions is as long as your arm. Often, sporadic (non-contagious) organisms like molds or environmental bacteria are implicated. Despite advances in diagnostic technology, many cases of bovine abortion go undiagnosed, mostly due to the fact that germs are not detectable by the time the fetus is expelled from the body.

Contagious causes of bovine abortion are occasionally found in cases submitted to SDSU. One of these infectious agents is quite interesting and fortunately fairly infrequent – Neospora caninum. Neospora is a protozoal agent with an interesting life cycle.

This life cycle starts off in a species of the canine persuasion – usually a dog or coyote. When infected, these animals don’t show illness themselves, but harbor the parasite and allow it to reproduce. Infective forms of Neospora leave the dog’s body through the feces. The protozoa an then get into a pregnant cow if the dog or coyote contaminates a hay source, mineral feeder, or other feed or water source by defecating in it. Neospora then travels through the cow’s gut to the bloodstream and the developing fetus. If it accomplishes its job of killing the fetus, then it’s expelled in the fetal tissues and placenta—which often happens to be a tasty meal for a dog or coyote. And the cycle starts again.

Fetal losses due to Neospora aren’t commonly diagnosed here; we’ve found about a dozen cases over the past few years. Of those cases, dairy herds are more often identified than beef herds, probably due to a higher level of observation and identification compared to the range conditions of most beef herds.

Beef herds have been diagnosed with Neospora in South Dakota; I recently spike with a producer dealing with it in their herd. This past spring a published case report of Neospora abortions in a souther US beef herd described pregnancy disruptions (abortions, stillbirths, premature calves, and non-calvers at the end of the season) to the tune of 55%. The effect of a Neospora exposure on pregnant cattle depends on the stage of gestation during which the cow is infected. Rapid fetal death (appearing as simple infertility) may occur in cows infected early in gestation. The fetus’ own immune system starts to kick in during the second trimester, meaning that it is more able to survive a Neospora infection the older it is. Most Neospora cases result in abortions between 4 and 6 months gestation.

A calf that survives to birth, however, can be persistently infected with Neospora. If this happens to be a heifer calf, she will produce infected calves herself should she become bred. Therefore in an infected herd, potential replacement heifers should be blood tested to ensure they are not going to give birth to infected calves. Remember that Neospora cannot be directly transmitted from cow to cow – the organism must work through the system of a canine and contaminate feed for transmission to occur.

Neospora may not be a common occurrence in our beef herds, but it illustrates some basic management steps that cattle producers should take to minimize problems of fetal loss in their herds:

1. When abortions occur, remove the fetus and cleanings from the area as soon as possible. This disease is just one example of the way these materials play a role in transmission.

2. Get a diagnosis. My rule of thumb is that one abortion may be just bad luck, but anything after that should get sent in. Talk to your veterinarian about what to submit. Don’t forget to send in cleanings too!

3. Prevent contamination of feed sources. It’s usually difficult to keep coyotes out of hay piles. But other feed sources (cake, minerals, other supplements) should be secured and if possible fed off the ground.

We may not be able to prevent every case of fetal loss in our cow herds every year. But as we learn more about these diseases, employing certain management practices can go a long ways in preventing losses.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at russell.daly@sdstate.edu or at 605-688-5171.