Antibiotics properly timed during PRRS virus outbreak reduce reproductive failure

An outbreak of porcine reproductive and respiratory syndrome (PRRS) on a sow farm will trigger reproductive failure in gestating sows. While PRRS is a viral disease, it causes endometrial inflammation leading to abortions, stillborns and mummified fetuses.

Ross Kiehne, DVM, with Swine Vet Center, conducted a study to evaluate the use of the injectable antimicrobial Draxxin® (tulathromycin) administered to gestating sows during a PRRS virus outbreak. Specifically, he wanted to see how administering the antibiotic at different stages of gestation affected the rate of reproductive failure.

On-farm investigation

The investigation was conducted on a 2,500-sow farm in northeast Iowa that broke with PRRS virus in mid-2019. The first 5-mL dose of Draxxin was administered to gestating sows 5 days after the outbreak was detected. A live viral inoculation (LVI) was performed 2 days later. A second round of the antibiotic was administered 13 days after LVI. About 20% of the sows were not treated, and these animals served as a control.

Data collected for the study was based on the pregnancy stage when the first antibiotic treatment was administered. The gestation stages were day 0-18, day 19-29, day 30-49, day 50-69, day 70-90 and day 91-105.

Kiehne used four reproductive outcomes for analysis: 1) abortions, culls and death; 2) farrowed and found open; 3) preg-check negative; or 4) repeat mating. The number of pigs weaned per sow was also determined for each animal enrolled in the study.

Positive outcomes in later gestation

The study verified Kiehne’s hypothesis that while administering Draxxin during early gestation is detrimental, it is beneficial during later gestation.

“Administering this antibiotic during early pregnancy appears to increase negative outcome events such as found open, preg-check negative and repeat mating,” Kiehne said.

“However, there appears to be an advantage to administering it in a PRRS virus situation after 50 days of gestation,” he continued. “This advantage is apparent in a reduction in abortions, stillborns and mummified fetuses and increase in total pigs weaned.”

Overall, the study found the percentage of sows that farrowed was higher for those given the Draxxin treatment at 68.5% versus 64.1% for the control sows with no antibiotic. Sows with abortions was lower for those receiving the Draxxin treatment at 17.4% versus 22.9% for the control group. Sows not pregnant was 6.9% for those given the Draxxin treatment and 6.7% for the control group. The deads and culls category was 7.2% for sows receiving the Draxxin treatment and 6.3% for the control group.

Weaned pigs per enrolled sow was calculated in each pregnancy group. In the early pregnancy stages, weaned pig averages were lower for sows receiving the Draxxin treatment compared to controls. After day 50 of gestation, the number of weaned pigs increased for sows receiving the Draxxin treatment compared to the control group.

In conclusion, Kiehne recommends administering the injectable antimicrobial Draxxin to sows after day 50 of gestation during a PRRS virus outbreak. However, administering it any earlier would be detrimental.