Ingredients for food and feed products perform many functions, but above all, they must serve as sources of essential nutrients. Even though an ingredient may be used because it adds a certain color to a product, or because it helps to physically bind other ingredients together, food and feed products are ultimately vehicles for performance through nutrition. Nutrient quality is made up of two main measures of any ingredient – the total amount of an essential nutrient, and the percentage of that nutrient that is used by the animal after consumption. Digestibility is a common measure of nutrient use, and is really the percentage of the total that disappears from the intestinal tract. Simply put, it is the amount removed from the intestine by absorption during normal digestion. A good example of how this technique is used to assess ingredient quality following differences in processing is shown in this video. While many nutrients are essential, it is the amino acids that make up protein that are often assessed for quality. This is primarily due to cost, as protein is almost always the most expensive nutrient in animal diets on a per unit mass basis. So, determining amino acid digestibility is common, and this information is used to prepare balanced formulations for livestock. Commodity, solvent-extracted soybean meal is frequently chosen, along with alternatively processed soy meals, including extruded, expelled soy meal. This ingredient is called ExPress® soy meal, and digestibility studies have indicated that animals fed this product will utilize more amino acids compared to commodity soybean meal. For example, according to data from Dr. Carl Parsons’ laboratory at University of Illinois, digestibilities of most amino acids were increased when properly processed ExPress® soy meal was fed to poultry (see below). Methionine, cysteine, and lysine, which often limit performance in poultry, digestibilities were all improved with the use of ExPress® soy meal. Leucine, one of the branched-chain amino acids, digestibility was improved about 3 percentage units. This is interesting because increased leucine promotes muscle (breast meat) protein synthesis in newly-hatched chicks. This could be very useful when trying to formulate starter broiler diets with minimal total protein to reduce costs.
Similarly, most amino acid digestibilities were improved when properly processed ExPress® soy meal was fed to swine in place of commodity soybean meal (see data below, and published article here). It is worth noting that the amino acids in the properly processed ExPress® soy meal were better utilized even though hulls were still present. Conversely, the commodity soybean meal was dehulled. Soy hulls provide dietary fiber, which is typically thought to hinder amino acid digestibility, although different fiber types exist.
Lastly, digestibility is important for ruminants, such as dairy animals, but in the opposite way initially. In order to support high lactation, and aid in transition periods (such as the beginning of lactation), some protein and amino acids must by-pass the rumen undegraded. The rumen is encountered first after consumption, and is a microbial fermentation vat. While it is important to support the microbial life in the rumen, it is critical to have sufficient amino acids for milk production. Some data from Dr. Marshall Stern’s laboratory at University of Minnesota is shown below – properly processed ExPress® soy meal exhibited not only higher rumen by-pass protein versus commodity soybean meal, but the protein that was undegraded in the rumen had higher digestibility in the intestine (after the rumen) to support milk production.
*“Effective processing” resulted in intestinally-absorbable dietary protein of 48.4% of the by-pass protein in ExPress® soy meal, and 30.1% in commodity soybean meal.
In conclusion, properly processed ExPress® soy meal is a higher digestible source of amino acids for livestock compared to commodity soybean meal. As such, ExPress® soy meal is a higher quality ingredient.