About three years ago, veterinarians coined the acronym PCVAD (porcine circovirus-associated disease) to describe swine health issues linked to circovirus.

Because of the high incidence of problems with circovirus, PCVAD was gradually replaced with the acronym PRDC (porcine respiratory disease complex).

At that time, PRDC described swine pneumonia caused by a combination of disease pathogens — primarily PRRS (porcine reproductive and respiratory syndrome), swine influenza virus (SIV), Mycoplasma pneumonia and different bacteria.

As the role of circovirus became more defined, incidence and severity of problems associated with the virus increased. Finisher death losses went from single to double digits, and respiratory problems worsened.

Diagnostics confirmed circovirus was a significant contributor, and the new syndrome warranted a new acronym.

But the recent introduction of effective circovirus vaccines has brought a dramatic decrease in PCVAD.

Swine respiratory problems still exist, however, meaning the industry is again faced with PRDC and opportunistic pathogens challenging pigs.

Case Study No. 1

This case history is from a 1,250-sow, farrow-to-finish operation that is PRRS- and mycoplasma-negative. The pigs are weaned to off-site, 1,000-head nurseries and then moved to 2,000-head finishing sites. Death loss in the nurseries averages 2.7% and finisher death loss averages 3.5%. Health and overall performance are good. The pigs are vaccinated with two doses of circovirus and SIV vaccines in the nursery.

Approximately six weeks after they are moved to the finisher, the pigs would develop a cough and decrease feed and water consumption. Death loss would increase slightly for about a week; then the pigs would recover and feed and water consumption would rebound back to normal.

At the time of this visit, we were unsure of the cause of this condition. The finishers are located in a relatively high-pig density area, so exposure from other pigs through aerosol transmission was possible.

We submitted tissues collected from postmortem examinations. The diagnostic laboratory identified PRRS virus and Actinobacillus suis. The pigs were negative for SIV, mycoplasma and circovirus.

Our assessment was that the pigs were being infected with PRRS virus due to area spread from other finishing pigs. We recommended that pigs in the nursery be vaccinated with a modified-live-virus PRRS vaccine. We are hopeful that control of the PRRS virus will result in control of the Actinobacillus suis as well. It is too early to measure performance, but so far the severity of the cough is less.

Case Study No. 2

A 3,400-sow, farrow-to-finish operation weans pigs into off-site, 2,400-head, wean-to-finish barns. This farm reduced wean-to-finish death loss from 12% to less than 5% when they instituted a circovirus vaccination program for weaned pigs more than two years ago.

Mycoplasma had never been identified as an issue in finishing pigs. Still, all replacement breeding animals were vaccinated for mycoplasma, and were given a pulse dose of lincomycin (Pfizer Animal Health) in the feed to help keep the sow herd stable.

However, one year ago, in an effort to reduce production costs, the farm eliminated this protocol. Just six months later, the farm experienced an increase in respiratory symptoms and death loss about 12 weeks postweaning.

Postmortem exams identified PRRS and mycoplasma as part of the pneumonia complex. We have since implemented a mycoplasma control protocol for the pigs following weaning, and also reinstated the previous mycoplasma control protocol used for the replacement gilts. Sixteen weeks into the new control protocol, health conditions are much improved.


With the continued economic challenges facing the swine industry, maintaining respiratory health in the grow-finish herd is critical.

Even though the widespread use of porcine circovirus vaccines have much improved pig health, respiratory disease still exists — and can quickly add to the cost of production.

Remember, the disease agents that are involved in a swine herd can vary depending on season, location and overall health of the breeding herd. Diagnostic technology exists to identify which pathogen or combination of pathogens is causing problems. Vaccine options and other management techniques exist that can address specific needs.

Working with your swine veterinarian to sort out what's involved in the disease complex will result in the most cost-effective disease control decisions. If you are experiencing production losses due to PRDC, contact your veterinarian as soon as possible.