Of all the diseases that impact growing and finishing pigs, chronic respiratory disease is the most economically important. Growth rates and feed intake are depressed and some herds experience heavy mortality. According to Managing Pig Health, by Michael Muirhead and Thomas Alexander, the control of respiratory disease requires an understanding of the complexities and interaction between the organisms that are present, the pig, and the management of the environment.

The authors write that the prevalence of respiratory disease is affected by the following factors:

  • Presence of respiratory pathogenic organisms
  • Virulence of the pathogens present
  • Level of the pathogens in the building environment
  • Immunity of the pig and the time of exposure to the organisms
  • Presence of secondary opportunistic bacteria
  • Interactions between management, environment, the diseases and the pig

Based on this list, one can see why Porcine Respiratory Disease Complex (PRDC) is difficult to manage.

Dr. Cary Honnold with Purdue Extension says, “Commonly, severe environmental stresses such as: chilling, temperature fluctuations, elevated humidity, overcrowding, frequent mixing of pigs, continuous flow production, excessive ammonia levels (> 50 ppm), and significant ascarid larval migration have been reported to predispose [pigs to] to development of PRDC. Environmental stressors, like the infectious agents associated with PRDC, can significantly suppress the pigs’ anatomic and cellular respiratory defense mechanisms.”

Various management practices may also play a contributory role in the development of PRDC. When Dr. Scott Dee was with the University of Minnesota, he reported that inadequate gilt replacement programs, large populations of pigs with subpopulations of immunity, wide ranges in weekly weaning ages, and commingling of piglets, were management practices that may help establish PRDC within a herd.

“When pigs from multiple sites are mixed with pigs having a different immune status, those harboring subclinical disease spread it to the other pigs which may be naive to that disease, and the result is outbreaks in the naive populations,” says Honnold. “Management practices such as mixing multiple sources of pigs into large nurseries, improper gilt replacement programs, and commingling of piglets with different levels of immunity, can lead to persistence of PRDC within a herd.”

More intensive production practices have made it more difficult to control PRDC. Susan Brockmeier with USDA’s Agricultural Research Service emphasizes the importance of proper ventilation and waste removal for the respiratory health of pigs. “Overcrowding and/or improper ventilation can lead to overheating or chilling, increased stress, and increased ammonia and dust levels which have a negative impact on the respiratory tract defenses. Many respiratory pathogens are so ubiquitous that it is hard to find a herd that is free from them; thus, it is not uncommon for herds to be circulating multiple pathogens at any given time.

To offset the obvious problem of keeping large numbers of pigs in a confined space, management practices have been developed to decrease infectious disease transmission and establish healthier herds. Dr. Matthew Turner, veterinarian for Prestage Farms, explains the importance of vaccinating before pigs show signs of PRDC to allow them to have the best immune response possible in this video. He also points out that proper management of sow flow and gilt acclimation are critical in minimizing not only PRDC, but other diseases in your herd. Click here to learn more.