Neospora caninum is one of the lesser-known causes of infectious reproductive failure in U.S. beef and dairy herds.
While cattle producers have long understood how certain viruses and bacteria affect reproduction such as bovine viral diarrhea (BVD) or leptospirosis, Neospora, which is a protozoal organism, provides some interesting challenges.
Transmission
The disease agent has a complicated life cycle that involves canines (dogs, coyotes, foxes) as an intermediate host.
Neospora infects cows after they eat feed that’s been contaminated by droppings from those infected intermediate hosts. If cows ingest Neospora organisms during pregnancy, they are apt to lose that pregnancy to an abortion or stillbirth.
Making matters more problematic, currently there are no marketed vaccines for this disease in cattle.
Danger to cattle
A troubling and somewhat unique aspect of Neospora is its ability to persistently infect calves born to infected cows.
Calves born infected with Neospora are outwardly healthy, but can themselves give birth to calves that are persistently infected, perpetuating the problem within a herd. Therefore, the Neospora status of replacement heifers within an infected herd may be something to consider when choosing those replacements within a beef herd.
Neospora blood tests
Blood tests that measure Neospora antibodies are readily available and a fairly reliable way to determine the Neospora status of cows and heifers.
South Dakota State University (SDSU) researchers recently worked with a northeastern South Dakota beef herd that had experienced reproductive losses due to Neospora, in order to prospectively monitor the number of infected replacement heifers over a number of years.
Replacement heifer testing
In the northeastern South Dakota beef herd, the producer was able to associate reproductive losses in their cow herd with Neospora infection, by comparing blood testing results of open cows with those of cows calving normally.
The herd then began testing their newly-bred replacement heifers for Neospora. While 2014-and-2015-born replacement heifers were not culled if pregnant, their calves were not kept for replacements.
Heifers born in 2016 and 2017 were tested at weaning and if they tested positive, they were not kept for replacements. The number of Neospora-positive replacement heifers declined in this herd in 2017. While other factors may influence this decline, it’s hoped that over time, as only negative replacement heifers are kept, the number of Neospora-positive animals will continue to diminish.
Some of the Neospora-positive heifers born in 2014 and 2015 still remain in the herd (although their calves are not kept for replacements). Any Neospora-positive heifers born in 2016 and 2017, however, were not kept as herd replacements.
Conclusions
It’s always possible for a beef herd to encounter new Neospora infections in a given year (via contaminated feed), but in herds in which it’s already established, using Neospora blood testing can be one consideration in choosing replacement heifers. Testing has the potential, in herds using home-raised replacements, to decrease the number of Neospora-positive animals in the herd over time.
Small numbers of these animals remaining in the herd may not significantly affect overall herd reproductive levels.
Any positive animal that remains in the herd, however, represents a possibility that Neospora could be transmitted (through canines) to other animals in the herd.
More information will be available soon and posted online at www.iGrow.org. — Russ Daly, professor, SDSU Extension veterinarian, state public health veterinarian; George Perry, professor and SDSU extension beef reproductive management specialist, and Holly Krueger, SDSU pre-veterinary medicine and animal science
