by Michaela Braun, Senior Liquid Systems and Sales Specialist, Novus, USA
Soybean meal is one of the most widely used protein sources in poultry and swine diets worldwide, valued for its amino acid profile, availability and cost-effectiveness. Yet even this cornerstone ingredient carries a persistent nutritional risk: naturally occurring trypsin inhibitors (TIs). These anti-nutritional proteins can reduce amino acid digestibility, impair feed efficiency and create hidden economic losses, particularly when they fluctuate unexpectedly from one shipment to the next.
For feed manufacturers, the challenge is not simply “eliminating” trypsin inhibitors but managing their variability and their downstream impact. The reality is that, while modern processing can help reduce TI, it does not consistently remove it entirely. Meanwhile, research increasingly suggests there is no truly “safe” level where performance is unaffected.
TI: Plant Defense with Feed Consequences
Trypsin inhibitors are defensive proteins found across many plant species, including soybeans. Their biological role is straightforward: they interfere with digestive enzymes in pests, protecting the plant from insect predation.
In livestock, however, the same mechanism works against production efficiency. Depending on the type of trypsin inhibitor, it may inhibit trypsin alone or both trypsin and chymotrypsin, two key digestive enzymes responsible for breaking down dietary protein. In soybeans, two major classes dominate: Kunitz trypsin inhibitor and Bowman–Birk inhibitor (BBI).
This distinction matters because TI classes differ in heat stability. The BBI is considered more resistant to heat and can inhibit both trypsin and chymotrypsin, making it a particularly persistent anti-nutritional factor under commercial processing conditions.
Processing helps but it has limits
Heat treatment is the most established approach for reducing TI activity because trypsin inhibitors are generally heat sensitive. However, soybean meal processing is not simply a “more heat is better” equation. It is a balancing act between lowering anti-nutritional factors and preserving amino acid availability.
Excessive heat can reduce the availability of essential amino acids, lysine being a well-known example, through reactions with carbohydrates and changes in protein structure. Overprocessing can also lead to denatured or altered proteins that become less digestible, effectively turning valuable protein into wasted nitrogen.
Critically, even commercially heated meals may still retain a meaningful portion of TI. Research in a new white paper from Novus indicates that processed soybean meals can retain up to 20 percent of both Bowman–Birk and Kunitz inhibitors after heating.
For feed mills, this creates a practical reality: processing reduces risk but it does not eliminate it. Assuming all soybean meal is “safe because it was toasted” is increasingly inconsistent with observed outcomes.
Why “No Safe Level” Changes the Conversation
Historically, the industry has treated TI as a threshold problem: below a certain number, there is no concern; above it, performance is impacted. But the evidence summarised in the white paper challenges that mindset, describing TI risk as incremental rather than binary. Even small increases in TI activity can translate into measurable losses, particularly in young animals.
In poultry, TI exposure has been associated with reduced ileal amino acid digestibility and pancreatic hypertrophy, a physiological response where the pancreas enlarges in an attempt to compensate by producing more digestive enzymes.
Importantly, hypertrophy does not “solve” the issue; digestibility reductions can continue in a linear fashion as TI levels increase. A 2020 study (Wedekind et al.) reported that for every 1 mg/g increase in dietary TI, amino acid digestibility decreased by 3.5 percent in broiler chickens.
A second-order risk emerges when protein digestion is impaired: more undigested protein reaches the lower gut, where it can fuel pathogenic bacteria like Clostridium perfringens. This can increase toxin production and damage the intestinal epithelium, compounding performance losses through gut health challenges rather than amino acid economics alone.
Trypsin inhibitors have also been linked to reduced swine performance for decades. Work by Araujo et al. (2025) indicates that each 1 TIU/mg increase was associated with an approximate 8-point increase in feed conversion ratio in pigs.
This box-and-whisker plot summarizes 1922 soybean meal samples analyzed by Novus with trypsin inhibitor (TI) concentration expressed in mg/g. Data are grouped by year to illustrate changes in central tendency and variability over time.
Why Testing Matters More Than Ever
If processing cannot guarantee a low-TI product, the only reliable alternative is measurement. Novus has studied soybean samples farmed around the world and found that TI levels are variable across years, regions and individual lots. In the dataset of more than 1922 soybean meal samples, over 75 percent were above 4.0 mg/g TI activity. The accompanying chart (Figure 1) shows substantial within-year variability, reinforcing that “average values” can hide high-risk lots.
This variability is the core reason soybean meal testing is not merely academic. It is a practical ingredient quality control tool that supports:
- Supplier evaluation (consistency over time)
- Lot-based decision making (diverting or blending high-TI loads)
- Targeted feeding strategies (protecting young or sensitive animals)
- More accurate formulation and cost forecasting
Analytical Considerations
TI results can be confusing because TI activity is reported using different units and methods. Under the AOCS Ba 12a-2020 method, TI activity may be expressed either as trypsin inhibitor units (TIU) per mg of sample or as mg of trypsin inhibited per g of sample. These values are directly related:
TI (mg/g) = TIU ÷ 1.5
A key caution for feed manufacturers is that results should not be compared casually across laboratories. Even when labs reference “the same method,” small differences in particle size, sample preparation, enzyme purity, extraction conditions or substrate selection can create meaningful differences in reported TI values.
Another complication is the existence of alternative international methods, such as ISO 14902:2001, which typically produce lower values than AOCS-based testing. ISO values may average around 55 percent of AOCS values and provide an approximate comparison factor:
AOCS-equivalent TI (mg/g) ≈ ISO TI × 1.8
These details matter because ingredient specifications can become misleading if the testing method is not clearly stated. For purchasing teams, a TI “number” without method context is not a meaningful quality guarantee.
Urease is not Proxy
Urease activity has historically been used as an indicator of heat treatment adequacy and sometimes as a surrogate for TI control. However, evidence suggests that the correlation between TI and urease activity is poor and that urease should not be used as a substitute indicator for trypsin inhibitor levels (Chen et al., 2020).
This is an important practical point: mills that rely on urease alone may believe they are managing TI risk when it’s likely that they aren’t.
Practical Risk Management
Since TIs are difficult to fully eliminate, feed manufacturers should treat TI management as a routine risk-control workflow, similar to mycotoxins or nutrient variability, rather than a one-time supplier qualification issue.
1) Test and segment ingredients by risk
Routine testing enables feed mills to identify higher-TI soybean meal and make informed decisions. The paper describes practical options such as diverting high-TI shipments to less susceptible livestock groups or blending high-TI meal into a more balanced ration to reduce exposure.
This approach recognizes that TI risk is not “all or nothing,” and that exposure management can be just as important as ingredient selection.
2) Align purchasing and nutrition decisions
TI risk management is not purely a formulation problem. It requires coordination between nutritionists and purchasers, because the “cheapest” soybean meal can become the most expensive when it reduces feed efficiency and amino acid utilisation.
Even modest performance shifts can affect cost per unit of gain, particularly in nursery pigs and young poultry where digestive systems are more sensitive.
3) Understand the processing trade-offs
Feed manufacturers should recognize that pushing for ever-lower TI via aggressive heat treatment can create new problems: overprocessing can reduce amino acid availability and generate less digestible proteins.
In practice, this means TI management should be pursued through a combination of controlled processing, validated testing and formulation strategies, not by assuming heat treatment can “solve it completely.”
4) Use nutritional tools strategically
Proteases are often included to improve protein digestibility but it’s important to know that most commercial proteases are not intrinsically effective against TI. Only proteases with demonstrated activity against TI proteins are likely to reduce TI-related losses.
From a risk-management perspective, this reinforces the need for:
- Measurement first (know the exposure)
- Tool selection based on evidence (not assumptions)
- Performance monitoring (verify response in the field)
Moving from Assumptions to Control
TI in soybean meal are not a new discovery but the industry’s understanding of their variability and incremental impact is evolving. The key message for feed manufacturers is that TI risk is lot-specific and processing alone cannot be relied upon to eliminate it without potential nutritional trade-offs.
Routine TI testing, paired with clear analytical interpretation, purchasing alignment and practical exposure management, gives mills a way to turn a hidden variable into a controlled input. In an environment where margins are tight and performance losses accumulate quietly, that shift from assumption to measurement may be one of the simplest ways to protect both animal outcomes and profitability.
For more information on the research provided here and the realities of TI, download the white paper Outsmarting Trypsin Inhibitors.
