Porcine reproductive and respiratory syndrome (PRRS) continues to be a big draw at our swine veterinary conferences and is the number one swine disease facing our farms.

Following are PRRS farm work-ups from our practice, and how we handled them.

Case Study No. 1

In the spring of 2002, I investigated a 300-sow, farrow-to-finish, single-site facility. Sows are bred and gestated outside. Pigs move through nursery and finishing facilities, all-in, all-out by room, but continuous flow by airspace.

The farm had mixed results with PRRS vaccination. At the time of my visit, sows and pigs were not being vaccinated for PRRS.

Clinical signs included severe respiratory challenges in the nursery and early finisher, over 10% mortality in the nursery, and and pigs very slow to go to market.

Pigs in all stages of production were blood tested. Tissue samples from nursery pigs were also submitted to the lab.

PRRS virus was isolated from lung tissues in nursery pigs. Serologically, pigs had exposure shortly after weaning, with titers peaking at 8-12 weeks of age. We isolated a field strain of the virus.

We recommended mass vaccination of the sow herd, twice, 30 days apart, with modified-live PRRS vaccine (Boehringer Ingelheim Vetmedica). We also began vaccinating piglets at processing time with the modified-live vaccine (extra label). This helped piglets develop immunity before entering the nursery. The herd stabilized and quieted down shortly after the second vaccination.

Sows were placed on a maintenance vaccination program for PRRS, parvovirus and leptospirosis one week prior to weaning. Production was very good for the next eight months.

Case Study Review

During a routine herd visit in February 2003, we again found several pigs in the nursery falling behind, with the “fuzzy” PRRS appearance. Several sows coming through the farrowing house had poor born alive numbers and poor milking performance.

Diagnostics again revealed PRRS activity in the nursery, and also higher-than-expected titers from the poor-producing sows in the farrowing house. Virus sequencing determined that it was a new field strain of the virus, unrelated to the strain isolated in the spring of 2002.

Treatment again consisted of two mass vaccinations of the sow herd, 30 days apart, using the same modified-live PRRS vaccine. We also continued vaccinating piglets at processing.

Further investigation revealed that the producer had purchased a set of early weaned pigs from a PRRS-positive source to fill in a gap in production. These purchased pigs never showed clinical signs like the home-raised pigs.

We also learned some of the sows in the farrowing house had been non-breeders through late summer/early fall. Several months had passed since their last PRRS vaccination.

It appeared the new PRRS strain was either from the early weaned pigs, or was an existing field strain which had not been identified and then surfaced in unvaccinated sows.

This herd has elected to mass-vaccinate sows quarterly and continue pig vaccination.

Case Study No. 2

A 1,200-sow, farrow-to-feeder pig farm was experiencing a high percentage of abortions at 18-24 days post-breeding, along with a smattering of late-term abortions. The recycles were classified as abortions because fetal tissues were passed by the sows and collected by the owner.

PRRS virus was isolated from submitted tissues and sequenced as a field strain. The herd had been PRRS-positive previously, and was using a killed PRRS vaccine (Intervet) in sows.

This field strain appeared more closely related to a new vaccine called PRRS-ATP, as compared to the original PRRS-MLV vaccine (both from Boehringer Ingelheim Vetmedica). Thus, the producer elected to mass-vaccinate the sow herd twice, 30 days apart, with modified-live PRRS-ATP.

The abortions diminished very quickly. Records from this farm did not demonstrate any elevation in pre-wean or post-wean mortality, and born alive numbers and farrowing rate are back to the herd's typical status.

The farm is now mass-vaccinating sows on a quarterly basis. No pig vaccinations are given.


These cases emphasize many points to remember when dealing with PRRS:

  1. Thorough diagnostics and case history are necessary before implementing PRRS control strategies.

  2. PRRS vaccine cannot be expected to provide 100% protection at all times.

  3. There can be risk involved introducing PRRS-positive animals, even into a PRRS-positive herd.

  4. There can be risk involved with extended time between PRRS vaccinations.

  5. Mass vaccination of the sow herd can stabilize health more quickly than “letting nature take its course.”

  6. Extra-label vaccination of piglets can allow more time for immunity to develop.

PRRS continues to challenge the industry. A thorough diagnostic workup is essential in understanding the strain you're dealing with, and where the virus is active. Only then can effective decisions be made to meet the PRRS challenge.