Many health challenges on today's swine farms are due to some type of viral disease problem no matter what stage of production is involved.
Porcine reproductive and respiratory syndrome (PRRS) virus and porcine circovirus type 2 (PCV2) by themselves cause severe disease conditions in growing pigs. When there is a mixed infection, the outcome can sometimes be catastrophic.
Often the best route for managing these viral diseases is prevention, either through vaccine strategies or production practices. Dual infections with both viruses present additional stressors on the pig, which significantly impacts the entire disease process and delays recovery.
Case Study No. 1
The owner of a 1,200-sow, farrow-to-finish farm had difficulty with the performance of the pigs in his off-site, continuous-flow nursery. The sow unit was PRRS-positive but stable. Nursery pigs developed a mild cough three to four weeks after placement. Many of the sick pigs became gaunt and went off feed. To make matters worse, finishing pig mortality topped 10% in the last six weeks prior to his call. Normal nursery and finishing pig mortality was 5% combined. Pigs were taking three extra weeks to make it to market weight.
Pigs were necropsied from the nursery and the finisher that were showing signs of respiratory disease. Blood samples were also taken from weaned pigs every four weeks, up to 18 weeks old. The diagnostics revealed that nursery pigs were PRRS-positive at 7 weeks of age. Serum antibody levels to PRRS virus were positive on 30% of the pigs at 7 weeks old, but nearly 100% positive four weeks later. The tissue samples from finisher pigs were positive for circovirus and had lesions compatible with a diagnosis of PCVAD (porcine circovirus-associated disease). I was puzzled by these results, considering that the farm was using a circovirus vaccine.
A followup discussion revealed the producer had been delaying circovirus vaccination so that the second booster injection had not been given when the cough started in the nursery.
Timing for circovirus vaccine is critical for adequate protection. So we revised the schedule to vaccinate at weaning and again two weeks later before the coughing started in the nursery. We decided to allow PRRS virus seroconversion temporarily because plans were being made to depopulate the nursery in the summer, since the sow farm was still producing negative pigs. Subsequent groups of pigs began to improve after these changes were made to control circovirus.
Case Study No. 2
A producer was purchasing pigs from a 500-sow, farrow-to-wean farm. He bought an additional flow of pigs from a nearby 500-sow farm. The nearby farm was recently depopulated, and the facilities were available for leasing. The producer wanted to supply this farm with gilts from the same genetic source as the current pig supplier so the health would be the same and he would be able to fill his finishing barns more quickly.
Two months after the off-site nursery had started to fill with the two similar pig sources, the producer called and said he was frustrated that the new weaned pigs from the gilt farm were not starting on feed, and were developing rough hair coats, diarrhea and coughing. They didn't respond to antibiotics. Mortality on the oldest groups weaned was already at 15% and increasing.
Samples were taken from both flows at weaning and from affected pigs in the nursery. Lab results indicated the new source of pigs was infected with PRRS virus during the start-up period and was viremic for PRRS virus at weaning. Pigs were positive to circovirus at entry to the nursery. The original source of pigs remained negative for both diseases at weaning.
The first step to controlling the disease pressure of mixing these flows was to stabilize the new sow farm to circovirus by vaccinating all gilts and sows with PCV2 vaccine. Although clinical signs were not observed at the sow farm, it was necessary to vaccinate so that the weaned pigs would have some maternal protection and to delay circulation of circovirus in the pigs.
The producer elected to initiate a PRRS virus control program on the new sow farm and continue mixing the two sources. All pigs entering the nursery were given PRRS vaccine. Groups in the nursery that exhibited signs of PRRS challenge were placed on liquid aspirin in the water.
Six months later, the new sow farm became PRRS virus stable and produced virus-negative pigs at weaning. All pigs entering the nursery from both sources continue to be vaccinated against PRRS and circovirus. The mortality decreased to 3% and clinical signs subsided.