With new soybean processing facilities in the Midwest, increased production of soybean meal may reduce its market price, making it a more accessible and economically as viable energy and amino acid source. Although soybean meal is the primary protein source used in swine diets in the Midwest, synthetic amino acids often replace much of the soybean meal in diets.
Researchers at South Dakota State University (SDSU) recently completed a study led by Courtney Pohlen to evaluate very high and low levels of soybean meal on pig performance and health. During the 111-day trial, 546 mixed-sex pigs per treatment were evaluated for the effects of diets with 1) low soybean meal inclusion supplemented with synthetic amino acids (5%) versus 2) high soybean meal inclusion (28%). All diets were formulated to meet or exceed NRC requirements and net energy (NE) levels were kept constant across treatments. Pigs fed high soybean meal diets gained weight faster than pigs fed low soybean meal diets.
“Our performance results in the high lean growth pig of today have consistently shown improved gains with soybean meal versus high levels of replacement with synthetic amino acids and/or dried distillers grains with solubles (DDGS). There is a sweet spot for growth rate for soybean meal use and its economics, but the faster growth is a definite indication that growing pigs metabolize SBM more efficiently than modelled in the past,” says Eric Weaver, SDSU assistant professor.
The researchers hypothesized that distinct populations of bacteria that degrade proteins and fiber from complex carbohydrates will be in higher abundance when pigs are fed with high inclusion diets compared to low inclusion diets.
“The proteins, polysaccharides and oligosaccharides of soybean meal can affect gut health and the microbiome through metabolic pathways that are not yet fully understood,” Angel Martinez, SDSU graduate research assistant, shared during the Allen D. Leman Swine Conference. “A better understanding of the effects of higher soybean meal inclusion compared to low inclusion on the swine gut environment and its microbiome is needed.”
Microbiome Composition
To explore the impact on the fecal bacterial composition and identify candidate gut microbial species, the team collected 14 fecal samples per treatment for DNA extraction and 16S rRNA sequencing via PCR amplification of the V1–V3 regions.
Martinez says a 16S rRNA gene-based analysis indicated significant differences in bacterial composition between the two treatments. They discovered a higher abundance of specific operational taxonomic units (OTUs) in the high soybean meal samples compared to the low soybean meal samples. OTUs are used in microbiome research to categorize and analyze bacterial diversity in samples.
“With soybean meal becoming more affordable, this study offers insight into optimizing energy and protein in swine,” Martinez says. “Results support the hypothesis that high soybean meal alters gut microbiome composition, potentially reducing the burden of amino acid metabolism on the body and influencing production of short-chain fatty acids and other metabolites for energy.”
Because of their higher abundance in samples from the high soybean meal diet, some OTUs may be associated with fiber degradation and utilization.
“These uncultured bacteria may still be undescribed, and further metagenomic analysis is needed to predict their metabolic roles,” he says. “In the long term, understanding these OTUs may clarify how polysaccharides and oligosaccharides are degraded in the swine gut and their role in short-chain fatty acid production.”
Researchers in this study included Martinez, Courtney Pohlen, Joseph Halbur, Eric Weaver, Benoit St-Pierre, all with South Dakota State University.
