Feed processing is basically designed to improve access to the grain contents, mainly starch granules, by digestive enzymes. Whole grains have a tough outer seed coat which is difficult to penetrate. Mastication by the molar teeth helps break open the seed coat, but often some portion of the grains or seeds consumed may be missed. Various methods have been developed to assist digestibility, the simplest being crushing rolling and grinding.
The ground grain can then be mixed with other ingredients and further treated to boost nutrient availability. In order of effectiveness the processes are:
Pelleting with Steam >>
Micronization (Conditioning with water then flattening and toasting under Infra-Red grill) >>
Extrusion (high temperature combined with high pressure cooking followed by forcing through a die). The feed expands violently when released from the die due to the change in external pressure.
The extruded product is sterile when produced and may have additional materials such as oil or temperature sensitive vitamins sprayed onto it before packaging. It provides the best percentage digestion of starch of any processing techniques, with about 95% of all starch being digested in the small intestine (vs approx. 60% for whole rolled grains). The selling point for extruded products is safety, by means of reducing the amount of starch entering the hind gut, and the overall improvement in feed digestibility.