How functional compounds in U.S. Soy help pigs weather respiratory disease and heat stress

19 January 2026

7 minute read

By: Sarah Mikesell

North America

As swine producers confront increasingly unpredictable health, disease and environmental pressures, new research is reshaping how nutritionists think about protein sources in modern finishing diets. 

Functional compounds naturally present in soybean meal derived from U.S. Soy are emerging as critical tools in protecting pig performance during respiratory disease challenges and seasonal heat stress – two costly disruptions to growth and feed efficiency in commercial production systems.

Respiratory pathogens continue to cycle aggressively through barns during the winter months, driving inflammation, reducing intake and creating extreme variation in body weights. Those consequences often linger long after clinical signs subside, reducing uniformity and exposing pigs to deeper losses during summer heat stress when consumption falls sharply. 

For Dr. Tom D’Alfonso, Worldwide Director of Animal Nutrition at the U.S. Soybean Export Council (USSEC), understanding the biological interplay between those two stress periods is key to preventing compounding economic harm.

At the center of the discussion is the role of inflammation, the body’s first defense against disease. And according to D’Alfonso, functional bioactive compounds in soybean meal derived from U.S. Soy, including isoflavones, saponins and bioactive peptides, can meaningfully influence the immune system’s ability to respond to challenges and recover performance.

Why inflammation and functional compounds matter

D’Alfonso explained that inflammation plays a central role in determining the degree of performance loss producers experience. 

“Inflammation is the body's first biological response to a challenge, whether it's an infection or an injury – even dietary changes can cause inflammation,” he said.

During respiratory disease events, he noted, pigs expend significant energy fueling an immune response rather than supporting growth or maintaining feed intake. 

“What we are seeing is that during respiratory disease, there is inflammation and other symptoms that occur,” he said. “However, there are a number of functional compounds in soybean meal that are positively affecting and alleviating the symptoms of respiratory disease when it happens and some of the carryover effects of what can happen later in the pig's productive life.”

The downstream impact is significant. An outbreak early in the year sets up deeper penalties when temperatures rise. 

“What we've also seen is in the summer during periods of heat stress, those animals that were affected by respiratory illness, and whose symptoms were not alleviated, continue to have performance issues and seem to be affected more by heat stress or what's called ‘the summer dip’.”

Why soybean meal works when synthetic amino acids do not

As heat stress depresses intake, producers often try to compensate with synthetic amino acids, medications or supplemental bioactive compounds. But research cited by D’Alfonso reveals that those approaches fall short of restoring gain.

“There are a number of different approaches to recover performance which may include medications, bioactive ingredients or synthetic amino acids,” he said. 

But despite these tools, he emphasized that producers face a fundamental limitation. 

“When feed consumption is down, you want to still make sure that the animal's getting the calories and the essential amino acids and other nutrients that are needed, and that's a real challenge when feed consumption is depressed,” he explained. 

His message is clear: research shows that soybean meal inclusion is the only nutritional lever that worked consistently.

“It was only by increasing levels of soybean meal that we were able to see the pigs recover performance during periods of heat stress,” he explained. “It wasn't demonstrated with synthetic amino acids or the other compounds in these experiments.”

Multiple modes of action working together

To understand why soybean meal performs differently, D’Alfonso pointed to the interaction of several immune and digestive pathways.

“To understand this, it's good to sort of step back and look at what are the core pillars of how a pig’s immune system responds to things like stress and pathogens,” he said. “I mentioned inflammation as being number one, but there's a whole series of things like macrophage activity, immunoglobulin synthesis and T-cell signaling, that also play roles.”

The functional compounds in soybean meal contribute to each of these mechanisms. 

“Isoflavones play a role in reducing inflammation, in immune modulation, in macrophage activity, and they're antiviral and antimicrobial,” he said. “Other compounds like saponins disrupt the cell membranes of bacteria. Bioactive peptides play a role in both immunoglobulin synthesis, and they play roles in antimicrobial modes of action.”

That combination, he said, appears to produce more resilient pigs that maintain digestion and immune stability. 

“These very interesting compounds are all acting on different mechanisms that an animal has to respond to a challenge,” he noted.

Uniformity, gut health and the economic reality of heat stress

Uniformity losses are sometimes overlooked, but they represent major financial consequences for finishing operations. Variable body weights force multiple marketing groups, lower packer efficiency and create higher mortality risk.

“Things like uniformity of the herd get affected because not all animals are affected or infected with pathogens,” D’Alfonso noted. “So what you see is an increase in the variability of body weight size.”

Higher soybean meal inclusion in the diet depending on stage directly influences that outcome. 

“Having high inclusion levels like 20%, 25% or even 30% in some cases of soybean meal alleviate those symptoms and make the animals and the entire population more resilient to heat stress,” he said. 

The reason, he explained, ties to digestibility and the interconnectedness of immune function and gut health. 

“Digestion implies that the ingredients are highly digestible, but it also has to do with the animal's ability to digest, which is very much dependent on the state of health of the gastrointestinal system,” he said. 

Synthetic amino acids cannot replicate this relationship. 

“Simply balancing the amino acid intake and the calorie intake isn't doing it,” he said. “Trying to balance with synthetic amino acids, bioactives, etc. did not recover performance, but adding soybean meal derived from US soy did.”

Rethinking formulation: The end of least-cost diets

The implications for formulation philosophy are significant. For decades, swine diets have been built around least-cost models targeted to basic nutrient thresholds. D’Alfonso argues that approach no longer reflects the economics of animal performance.

“First, we need to move beyond least cost diets that merely meet the animal requirements based on decades old standards,” he said. “Because new research shows that there are minimum levels of important ingredients like high quality soybean meal that should be in the diet.”

That shift requires re-examining what feed truly costs. 

“If you're formulating a diet, you should include a minimum soybean meal of 25% during some periods of time and take a close look at the economic consequences of not doing so,” he said. 

The cost of avoiding soybean meal, he warned, is hidden in lost uniformity, reduced gain and weaker feed conversion. 

"You're going to have less uniformity, higher mortality, poor feed conversion, poor rate of growth and poor consumption, and all those are costs that are presently not included in a least cost feed formula,” he said. 

Forget crude protein

When asked to summarize the single most important message for producers reconsidering their protein choices, D’Alfonso responded unequivocally.

“We've talked about some exciting things like functional compounds, the essential amino acids that metabolizable energy, their role in the animal, soy as a foundational ingredient and the immune system working together,” he said. “I don't think I mentioned crude protein a single time in our conversation.”

And that is intentional. “The strategy for managing protein is honestly to forget about crude protein. It's a red herring,” he explained. 

Instead, he encouraged a new standard grounded in digestibility and consistency. 

“Move away from crude protein and move to formulating on digestible, essential amino acids and metabolizable energy. Take into account the consistency of the ingredients. Soybean meal made from U.S. Soy is highly consistent,” D’Alfonso emphasized. 

The combination, he said, unlocks measurable returns. 

“You'll save money on feed formulation by getting the numbers correct. But then the next step is fixing minimum inclusion levels of soybean meal in the diet by following the recommendations of the research that has been published called The Soy Effect,” he said. 

The path forward

As the industry continues to battle respiratory pathogens, the summer dip and rising economic pressure, D’Alfonso believes the path forward will depend on recognizing the underestimated power of ingredient-based immune support.

Producers, he emphasized, cannot afford to overlook the compounding effects of early disease on later heat stress vulnerability nor the performance and economic benefits associated with minimum soybean meal inclusion levels that provide not just nutrients, but recoverable resilience.

When performance, health and economic return intersect, the message is simple: soybean meal derived from U.S. Soy is more than a protein source – it’s an immune and digestive support system the modern pig depends on.

This information was partially funded by the U.S Soy Checkoff.