Impact of Neospora-Positive Status on Heifers/Cows and Their Calves

About Neospora
Neospora caninum is a protozoal germ that has the potential to affect reproduction in beef and dairy herds. The protozoa has an interesting lifecycle that involves canine species (dogs, coyotes, foxes, etc.). When Neospora-affected cows give birth, the cleanings and fetal tissues contain Neospora cysts. If these tissues are eaten by a canine, Neospora oocysts are shed in their droppings. When these infected droppings contaminate cattle feed, the cycle is complete, infecting cattle that eat the feed.

Impact on Cattle Reproduction
Neospora-related reproductive problems can arise from two different kinds of infected cattle: 1) cows or heifers that became infected by eating contaminated feed, and 2) cows or heifers that were born with Neospora and pass it on to their offspring in utero. Reproductive issues usually occur in the form of abortions, which may be early enough in gestation to be unnoticed by the cattle caretakers.

While Neospora-positive females are more likely than negative females to suffer reproductive failure, these occurrences are not universal – some infected animals give birth to normal calves, while others abort or have calves that are persistently infected.

Recent Research
SDSU researchers worked with a South Dakota commercial beef herd to help understand the relationship between reproductive failure and Neospora-positive status. An earlier iGrow article described the herd’s use of serology to select replacement heifers.

Pregnancy Observations
In this herd, replacement heifers were pregnancy tested via ultrasound and follow-up palpation, and blood sampled for Neospora caninum serology at the same time. Data on 2 groups of replacement heifers was obtained (2015 and 2016 pregnancy checks), in addition to resident adult cows bled and pregnancy checked in 2016 (Table 1).

In heifer groups, being positive for Neospora was associated with an increase in the risk of being open, although statistical significance was only noted in the 2015 breeding year. In contrast, in adult cows, a seropositive status was associated with a decrease in the risk of being open. This was not a statistically significant relationship, however.

Transmission to Calves
The serostatus of resident adult cows was compared with serostatus of their progeny in 108 cows for which data was available. In this herd, seropositive cows were 13.43 times more likely to give birth to a seropositive calf compared to seronegative dams, a statistically significant finding. Neospora-positive cows had positive progeny 87% of the time, compared to 5% of the time for Neospora-negative cows. In this herd, at that particular point in time, endogenous transmission from infected mother to calf appeared to be the most significant route of transmission.

Conclusions/Significance

• For this particular herd, Neospora-positive heifers were at higher risk of reproductive failure compared to negative heifers, although statistical significance was demonstrated in only 1 of 2 years.
• Neospora-positive adult cows were more likely (but not statistically significantly) to be pregnant compared to negative cows, suggesting age- or immune-related protection against reproductive failure.
• Seropositive cows that retained their pregnancies were at significantly higher risk of giving birth to a congenitally-infected calf compared to seronegative cows.

In this herd, culling Neospora-positive replacement heifers could positively influence herd reproductive performance. Using Neospora serologic status to make culling decisions in the older cows, however, could be counterproductive to herd reproductive performance. Serologic profiling for Neospora could be useful as one factor in reproductive decision-making in a commercial cow-calf herd.

Source: Russ Daly, DVM, DACVPM, iGrow