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Minimizing the Neospora Threat by Using Serology in Beef Replacement Heifer Selection

Updated September 28, 2020
Russ Daly

Russ Daly

Professor, SDSU Extension Veterinarian, State Public Health Veterinarian

Blood sample sitting on a countertop in a veterinary lab.

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.

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 is worth considering 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 have 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.

In this article, the herd’s efforts in using Neospora serology to help select replacement heifers is described. Another article, Neospora-Positive Status: Impact on heifers/cows and their calves, has examined the relationship between Neospora serostatus and subsequent pregnancy success.

Using Neospora Serostatus in Selecting Home-Raised Replacement Heifers

Line graph showing Neospora testing results for replacement heifers from 2014 to 2020. There is a significant decline in positive test results between 2016 and 2020. For a complete description, call SDSU Extension at 605-688-6729.
Figure 1. Neospora testing results for replacement heifers, South Dakota commercial cow-calf herd, 2014-20.

In this 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 following years were tested at weaning and not kept for replacements if positive.

The number of Neospora-positive replacement heifers has declined since 2017 (Figure 1). While various factors may have contributed to this decline, using Neospora serology in the culling criteria over a period of years is one major management change that likely has some great influence. Some of the Neospora-positive heifers born in 2014 and 2015 still remain in the herd, but beginning in 2016, Neospora–positive heifers are not kept as herd replacements. By not keeping persistently-infected females in the breeding herd, the number of Neospora-infected calves born in the herd has declined over time. These results also affirm the observation that no new introductions of Neospora have occurred in the breeding herd over this time.

Conclusions/Significance

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.