Soy Allergy Modeling Will Benefit Pigs and People

Animal feed products use nearly all U.S. soybean meal. One of the top priorities to emerge from the recent Soy Industry Connections Workshop focused on the need to develop enhanced soybean products that help sustain and expand the U.S. poultry, livestock and aquaculture industries. Certainly, feed is the major variable cost in livestock production, and increased volatility in the corn and soybean markets is likely to be a long-term trend.

However, the quest to reduce feed costs with distillers" dried grains, synthetic amino acids and cheaper forms of carbohydrates and fat may sacrifice productivity and/or meat quality in pork, poultry and aquaculture operations. So, many animal scientists now consider customized dietary intervention to pre-empt enteric disease, improve feeding efficiency and nutrient absorption, as well as to reduce mortality rates in livestock production. Certain changes in soybean composition may contribute to dietary interventions that improve livestock performance, mitigate problems with livestock waste and emissions from volatile organic compounds, and even help reduce subtherapeutic antibiotic use.

Although soybean genomics and biotechnology offer seemingly infinite possibilities for changing soy-protein composition, high throughput and accurate and cost-effective evaluation techniques also are needed to determine which soybean-protein quality traits will be most beneficial to livestock production. For many reasons, most available evaluation methods in use often are inadequate for this task.

Unlocking New Approaches

Advances in formulating rations that improve the animals" ability to digest and absorb dietary nutrients may come from the study of human food allergies. In 2006, the Food Allergen Labeling and Consumer Protection Act included soybeans in a list of major food antigens.

An antigen is a substance, usually a protein, that may trigger the formation of antibodies which can bind to the antigen and cause an immune response. Certain soy proteins bind immunoglobulin (antibodies) and may cause food allergy symptoms in sensitized humans. Researchers do not fully understand the mechanism for this diagnosis, but it may follow a similar biological path in pigs.

According to an article published in the Journal of Nutritional Biochemistry by Sun et al., soy-protein-induced hypersensitivity in pigs is predominantly a Th2-type immune response. Piglets experiencing this malady suffer from diarrhea and reduced growth performance when first exposed to feeds containing soy products.

Currently, no accurate method exists to determine threshold levels for potential antigens in feed ingredients. There is no way to distinguish antigenic properties among soy proteins and no reliable or cost-effective way to evaluate the human or animal response to dietary changes in feed ingredient composition.

Building the tools needed to overcome these roadblocks may be the best way to move forward in a timely manner. As a first step, a research partnership between the National Pork Board, United Soybean Board/Soybean Checkoff and Qualisoy has been formed in support of the project, known as Development of an Allergenicity Model in Swine. Hogs were chosen for the model because swine emulates the human immune response better than any other species.

Modeling the Future

Many models are used in the clinical study of allergy and anaphylaxis (dog, rat, monkey, humanized mouse and pigs). Each has limitations. For example, sensitized neonatal pigs exhibit highly variable immune responses to dietary challenge. This variability significantly compromises interpretation and comparison of dietary treatment effects.

The NPB-USB-Qualisoy project makes two major improvements to the swine model as it uses:

  • Pig lines that are genetically selected to give a uniform immuno-sensitive response to soybean meal.
  • ELISA assay that deploys two monoclonal anti-swine antibodies to measure IgE and IgG immunoglobins produced in sensitized piglets challenged with feed containing soybean proteins.

This work has provided evidence that hyper- and hypo-sensitivity to dietary proteins are heritable traits in pigs. Uniformity in the pig lines also makes it easier to develop genomic tools to implement swine breeding strategies for these traits.

Preliminary tests show that the improved swine model can distinguish differences in immune response to soybean meal that contains different genetic modifications in protein composition. This ability provides a means to define the mechanisms that mediate how gut tissues recognize and respond to antigens.

The tests also show that the ELISA assay recognizes soy proteins but not peanut proteins. This removes much interference and enhances the ability to develop genomic tools that can distinguish genes for soy antigens that elicit allergy from those that don't.

The next phase of this work will involve:

  • Validating the modified swine model.
  • Developing accurate profiles of expressed swine genes that protect or cause membrane inflammation.
  • Using the gene profiles to develop customized gene chips for high-throughput screening of soy-allergen-induced gene expression.

From Pigs to People, and Back

Although the "swine model" will facilitate the study of human allergy, there are many applications that will benefit pork producers. For example, the customized swine gene chip can enable marker-assisted pig breeding strategies for hypo-sensitivity to soybean meal. The chips also may prove invaluable to the nutritionists who monitor dietary effects on nutrition, manure emissions and animal health.

In addition, the chip may help soybean breeders selectively engineer and "identity preserve" new varieties with reduced immunogen potential. Varieties that help reduce the number and severity of allergic responses in swine (perhaps poultry and carnivorous fish species as well) could allow the inclusion of more soy in pork production. Such an achievement would provide the pork industry with options and flexibility to alleviate diet-induced immune-related disorders that contribute to allergy and to less than optimal livestock performance.

So, a tool needed for the study of human allergy also will benefit pork producers. One day it may be possible to grind and feed soybeans with minimal processing, as some feed industry experts envision. Such advances in agricultural technology and the opportunities they may enable would not be achieved without the support of the NPB, the USB/Soybean Checkoff and Qualisoy. The future will teach us more.

Richard Wilson, Oilseeds &; Biosciences Consulting, previously worked at USDA's Agricultural Research Service as a national program leader or the Soybean Research Program.