The Hidden Cost of Heat Damage: Why Soybean Meal Origin Affects What Pigs Actually Absorb 

By Thomas D’Alfonso, Ph.D., Worldwide Animal Nutrition Focus Area Director, USSEC 

New university research confirms what quality-focused nutritionists have long suspected: heat damage to soybean meal – a known problem in many international origins – quietly erodes pig performance. And no amount of reformulating fully gets it back. 

Consider a scenario familiar to many swine nutritionists: a diet formulated to look perfectly balanced on paper. The right protein, the right amino acids, yet pigs consistently come up short at the scale. A team of researchers at the University of Illinois set out to quantify exactly why. 

The problem shows up most often when soybean meal comes from origins with less consistent processing controls. Research comparing soybean meal from the U.S., Argentina, Brazil, China and India shows measurably higher nutrient variability and greater heat damage indicators in South American origins.      

In the U.S., soybeans naturally field-dry in the Midwest climate before harvest, arriving at the processing plant with lower moisture levels. Less moisture means less heat is required during processing. That is a key reason soybean meal derived from U.S. Soy is less vulnerable to heat damage.  

This research puts hard numbers on exactly what is at stake when that consistency is absent. 

The Invisible Problem: Heat Damage 

Soybean meal must be heated during processing to destroy antinutritional factors that would otherwise harm animal health. But there is a narrow window. Too much heat triggers a Maillard reaction. This is the same chemical process that browns bread and caramelizes onions. In soybean meal, that reaction binds lysine, the critical first-limiting amino acid in swine diets, into a form pigs simply cannot use. 

Researchers L. Torrez-Mendoza and H. H. Stein at the University of Illinois fed 160 weanling pigs diets made with soybean meal processed at three heat levels: normal, moderately overheated and severely overheated. In the severely overheated group, reactive lysine – the bioavailable form pigs can use for muscle growth – dropped 44%, from 2.84% to just 1.59% 

The result: 

By day 28, pigs fed the severely heat-damaged diet weighed nearly 3 kilograms less than pigs fed the control diet, a statistically significant difference (P < 0.001).² The performance gap translated directly into days to market, feed conversion and margin. 

Can It Be Fixed? Not Entirely. 

The researchers added crystalline amino acids to the heat-damaged diets to compensate for the lost lysine – essentially reformulating to match what a properly processed diet would deliver. 

The intervention helped, but it did not fully restore performance. Pigs on the corrected diet improved relative to those on uncorrected damaged meal but still trailed the control group in final body weight, feed intake and growth efficiency.² The researchers believe heat damage may also reduce energy digestibility – a consequence that amino acid supplementation alone cannot address. 

The conclusion: Reformulation cannot fully compensate for a processing quality problem at the source. 

Why Soybean Meal Derived from U.S. Soy Delivers – Consistently 

The implications for producers and nutritionists are clear: sourcing matters. 

Studies comparing global soybean meal quality have found that meals from South American origins – particularly Brazil and Argentina – show significantly higher variability in processing quality, with more frequent instances of heat damage reflected in lower reactive lysine and reduced protein digestibility.¹ At the same crude protein level on the label, those meals can deliver meaningfully less usable nutrition. 

The industry measures processing quality with two key indicators: 

Research from USSEC’s Soy Excellence Center network and published comparisons of global soybean meal quality show that soybean meal derived from U.S. Soy maintains reliable protein quality indicators – including reactive lysine levels – across a wide range of production and export conditions. 

In contrast, meals from some international origins show higher variability in processing quality, with elevated rates of heat damage reflected in lower amino acid bioavailability – even at the same stated crude protein level.¹ 

When moderate heat damage is enough to reduce gain-to-feed ratio and average daily gain – and when corrective reformulation falls short – sourcing from a reliably processed origin is not a premium. It is risk management. 

For the Full Research Summary 

The U.S. Soy Center for Animal Nutrition and Health (CAN) hosts the complete research summary – including methodology, data tables and production implications – for nutritionists and producers seeking additional detail. 

→  Read the Full Research Summary on U.S. Soy CAN 

Partially funded by the Soy Checkoff. 

¹ Chemical composition and amino acid digestibility of soybean meal produced in the United States, China, Argentina, Brazil, or India, L. V. Lagos and H. H. Stein, Journal of Animal Science, 95(5):1626–1636, 2017 

² Effects of heat damage and crystalline amino acid supplementation on growth performance of weanling pigs fed soybean meal and enzyme-treated soybean meal, L. Torrez-Mendoza and H. H. Stein, University of Illinois, Swine Web, December 2, 2025 

³ Official Method Ba 10a-05: Protein Dispersibility Index (PDI) of Soybean Products, American Oil Chemists’ Society (AOCS), AOCS Press; see also: National Oilseed Processors Association (NOPA) Trading Rules for soybean meal quality specifications 

⁴ Nutritional value of soybeans as affected by heating, C. M. Parsons, et al., University of Illinois, Poultry Science, 1991; 70(8):1718–1723; see also: USSEC Technical Bulletin on Soybean Meal Quality Indicators (KOH Protein Solubility)