Taking a cue from what is known about improving human health through the use of soy and other bioactives, new research at the University of Illinois has found that increasing concentrations of soybean meal (SBM) in the diets of weanling pigs, above industry standards, may be beneficial for pigs that are infected with the porcine reproductive and respiratory syndrome virus (PRRSV).
Ryan Dilger, a U of I animal scientist who led the research said that the study was prompted by an observation reported from a large-scale commercial farm where pigs who were already on a higher SBM diet became less sick during a PRRS infection.
Currently, porcine reproductive and respiratory syndrome (PRRS) is the most prevalent disease of swine globally. Young nursery pigs infected with the virus experience symptoms of fever, lethargy, respiratory stress, reduced feed intake, and ultimately decreased growth performance.
Dilger said he wanted to find out if PRRS-infected pigs that were fed a higher concentration of SBM in their diet would exhibit positive body weight gain during the time of infection, as well as experience a shorter duration of illness. Compared to PRRS-infected pigs that were not fed a higher SBM diet, they did.
Soybean meal is the primary dietary protein source for swine in the United States. Soy-derived feedstuffs contain a number of biologically active compounds, including isoflavones, which may have been the key to reduced illness in the PRRS-infected pigs in the study.
“All this fits under the umbrella of looking for alternatives to antibiotics,” Dilger said. “We are looking at alternative strategies we can use to keep promoting health during that time [of infection]. Increasing soybean meal, something that is already used in swine formulations, is simple and effective and maybe an important approach for the industry.”
Typically, SBM is limited in the diets of newly-weaned pigs because of the still developing gut’s inability to digest the nutrients, which can result in symptoms such as diarrhea and a reduction in food intake and growth. After weaning, the diet typically contains around 17 percent SBM, Dilger explained.
As part of the study, PRRS-infected weanling pigs were fed a common diet for one week and then one group was put on a high SBM diet of 29 percent SBM, with another group put on a low SBM diet of 17.5 percent for two weeks.
During the two-week period of infection, blood tests showed less virus and fewer inflammatory markers circulating in the bloodstream of the pigs on the high SBM diet than in those on a low SBM diet. Fewer inflammatory markers may indicate an altered immune response, which appears to influence both the magnitude and duration for the infected pigs, Dilger explained.
“We still don’t know exactly why this is happening. This was a proof of concept study, but we do know that the immune response is part of it,” Dilger said. “Feeding a higher concentration of soybean meal elicited an improved immune response, and the next step is to identify whether this was caused by isoflavones or something else.
“We speculated that it is the isoflavones, but we couldn’t disentangle that in this particular study,” he added.
Isoflavones are proven bioactives that are often emphasized in human nutrition and are known for having antiviral effects, Dilger explained. “We know they are present in soybean, so we quantified the amount, and we know that the diets with more soybean meal had higher isoflavones concentrations.”
Because soybean meal also provides amino acids, Dilger said they are also looking into the effects of the amino acids in the pigs’ diets during infection.
Dilger also pointed out that in healthy pigs, there is less benefit of a higher SBM diet. “But if you know your farm is at risk, then higher inclusion of SBM may serve as insurance,” he said. “Soybean meal is expensive, so if you put it into the diet and it doesn’t do anything, you’ve wasted money.”
“Nutrition won’t prevent the infection, but it may lessen the negative effects,” he added.
The research in the current study is building on previous U of I work with animal sciences professor emeritus James Pettigrew, looking at the effects of plant extracts on pigs with both PRRS and E. coli infections.
“Dr. Pettigrew and I have been working to extend the PRRS model to other bioactives,” Dilger said. “Soy is just another plant extract, but a bioactive with benefits. We’re just extending that story.
“Every pig and chicken is going to receive soybean meal so we are looking to add value to soybean in terms of promoting health and lean tissue accretion,” he added.
“Effects of dietary soybean meal concentration on growth and immune response of pigs infected with porcine reproductive and respiratory syndrome virus” was recently published in the Journal of Animal Science. Co-authors include S.J. Rochell, L.S. Alexander, G.C. Rocha, W.G. Van Alstine, R.D. Boyd, J.E. Pettigrew, and R.N. Dilger.