High-Shear Dry Extrusion Shows Poultry Digestibility Improvements
The amino acids that make up proteins are critically important in any diet. Typically, in order to build proteins, all amino acids are needed. Commercial diet formulations often focus on lysine and methionine levels, as these tend to be limiting to growth and efficiency. However, when formulating least-cost diets, other amino acids often come into play as well. There are two sulfur-containing amino acids that make up proteins – methionine and cysteine.
Heat processing, which deactivates trypsin inhibitors and other anti-nutritional factors, is needed to make high-quality soy meals that enhance animal growth. It should be noted that one type of heat processing does a markedly better job of promoting the digestion of sulfur-containing amino acids than others: high-shear dry extrusion. In the case of cysteine digestibility, high-shear dry extrusion is far superior to other methods (data from Dr. Carl Parsons, University of Illinois).
As seen in the graph above, high-shear dry extrusion does something unique to free up cysteine in soy proteins. A 5–6% improvement in digestibility represents a significant processing advantage. The heating process for hexane extraction and those achieved with expanders produce very different results, making access to cysteine during digestion much more difficult.
Remember that cysteine is used in proteins to give structure and function, and one important group of proteins in soy is the trypsin inhibitors. For example, one soy trypsin inhibitor contains seven cysteine pairs that help the protein maintain its structure and function, which can interfere with protein digestion (see here). Vastly improved cysteine digestibility following proper processing with high-shear dry extrusion can also indicate better anti-nutrient deactivation, providing a higher-quality meal. Additionally, feathers are rich in these amino acids, resulting in higher dietary requirements for chickens.
What does this mean for formulations? When using high-shear dry extruded soy meals in, for example, broiler formulations, premiums can be realized from $30-60/ton for meal. Part of this advantage is due to improvements in amino acid digestibility, including cysteine.
For more information on digestibility analysis of extruded ingredients or how our processing techniques can benefit your operation, please consult our nutrition team.
