In the November issue of the Journal of Nutrition, scientists at the University of Illinois at Urbana-Champaign report that the production of inflammatory cytokines by immune cells appears to be responsible for declines of both protein accretion and weight gain in swine infected with Porcine Reproductive and Respiratory Syndrome Virus (PRRSV).
The study also suggests that myostatin, a protein that limits muscle growth, is overproduced during infection, thereby reducing the growth of skeletal muscle, said Rodney W. Johnson, a professor in the department of animal sciences and the interdisciplinary Division of Nutritional Sciences.
Johnson and colleagues isolated pigs in disease-containment chambers and exposed different experimental groups to the bacterium Mycoplasma hyopneumoniae and/or PRRSV.
Almost all U.S. swine are exposed to the bacterium in production facilities, while about 60 percent are exposed to PRRSV. These pathogens open the way for other infectious agents. During the pivotal growing stage, pigs are at the most risk and suffer from cough, fevers and depressed appetite. Reduced market weight or increased time for pigs to reach a desired market weight can be a substantial cost to producers.
Infection from the bacterium alone did not reduce weight gain compared with the control group during the four-week-long experiment, but it did lead to the development of lesions that affected 8 percent of the total lung area in infected pigs. The finding was similar to earlier work in Johnson's laboratory. However, the introduction of PRRSV caused damage to the lungs from the bacterium to jump to 40 percent.