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 (e.g., BVD virus or leptospirosis), Neospora (a protozoal organism) provides some interesting challenges. 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, there are no currently marketed vaccines for this disease in cattle.
Danger to Cattle Herds
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.
Blood tests that measure Neospora antibodies are readily available and a fairly reliable way to determine the Neospora status of cows and heifers. 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.
Blood Testing & Heifer Replacement Strategy
In this article, the herd’s efforts in using Neospora serology to help select replacement heifers is described. A subsequent article will look into the relationship between Neospora serostatus and subsequent pregnancy success.
In the herd observed, reproductive losses in cows and heifers calving in the spring of 2015 were associated with those animals being positive for Neospora antibodies on blood testing. 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 not kept for replacements if positive.
Although the number of Neospora-positive replacement heifers declined in 2017, it’s not clear whether using Neospora serology in the culling criteria played any role. 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.
Table 1. Neospora testing results for replacement heifers, South Dakota commercial cow-calf herd, 2014-17.
|Year of birth||Number tested||Number positive (%)|
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 serology can be one consideration in choosing replacement heifers. This 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.