Processing Improves Grain Digestibility in Horse Feeds By Kentucky Equine Research Staff · May 21, 2012
The grains in most of today’s feeds are processed in some manner before being fed. Although some grains can be fed whole, processing, even if it is only grinding, usually makes the nutrients more available to the animal, thus improving digestibility and feed efficiency.
Grinding is done using either a hammermill or roller mill. Hammermills grind primarily by the impact of free-swinging hammers on the grain as it falls through the grinding chamber. Screens with specifically sized holes surround the grinding chamber and as the grain particles become small enough, they pass out through the holes. Roller mills have pairs of rolls, often two or three pairs per mill, that crush the grain as it passes between the rolls. The space between rolls can be adjusted to give various particle sizes.
Popping is achieved by rapid, intense heating of grain. Rapid heating with 700 to 800° F (371 to 427° C) hot air makes the moisture in the kernel turn to steam, thereby expanding the grain. Most feed grain does not pop like popcorn, but grain does expand and starch is gelatinized, resulting in the grain being much more available to digestive enzymes or organisms. Because popped grain has a larger volume per weight, it also contains a lower level of nutrients than the same volume of unpopped grain and sometimes an animal cannot consume sufficient feed, resulting in reduced gains. Many users roll the popped grain to increase the bulk density and to help flatten the grain for easier handling.
Roasted grain is similar to popped grain except the grain is heated at a much slower rate. Grain is passed through a rotating drum which lifts the grain through a flame. Grain temperatures reach 260 to 300° F (127 to 149° C). Water is lost without causing much expansion. Depending on the rate of heating, the starch may be gelatinized and some puffing may occur.
In dry-heat processing, because of the dry heat sources and the limited amount of water available within the grain, very little nutritional damage occurs during normal processing. Obviously, if the grain is overprocessed (overheated) during any of these processes, damage will occur. This is normally not a problem as each process requires a large amount of energy, and thus expense limits overprocessing. A more frequent problem is underprocessing, again due to energy costs. Although this does not harm the grain, it is wasteful because there are no added benefits if it is not done correctly.
Steam flaking has become a very well-defined process. It is the most popular method of processing feedlot grains. Steam flaking differs from steam rolling in the amount of time used to steam the grain. Flaking calls for a longer conditioning time that is sufficient to gelatinize some of the starch. Grain is conditioned at atmospheric pressure for 15 to 30 minutes. Grain temperatures should reach 200 to 210° F (93 to 99° C) with moisture around 17-18%. The amount of starch gelatinization depends on heat, moisture, and roll pressure. Studies conducted on steamed grain before and after rolling show most of the changes in starch occurred after the rolls. Properly flaked grain results in improved feed efficiency and rate of gain. If the grain is not properly flaked, starch will not be gelatinized and there will be no benefits that could not have been achieved by dry rolling. Steam-flaked grain must be fed relatively soon after flaking or it must be dried. In most operations, the added expense of drying the flakes makes it impractical. Steam-flaked grains are often used in textured horse feeds and it is critical that the grain be properly dried or it will begin to mold almost immediately. Frequently when corn is flaked, the germ is dislodged from the remainder of the kernel. Often, if dryers are not properly adjusted, this material can be blown out and lost as air is being passed through the drier. If this happens, the energy content of the flaked grain drops somewhat due to the loss of oil and protein.
Pelleting is the most common form of thermal processing used in horse feed manufacturing. Feed is heated by steam in a conditioning chamber, raising the temperature and moisture content. The temperature and moisture reached depend on the length of time spent in the conditioner. Temperature may range from slightly above ambient if little steam is added, to nearly 200° F (93° C). Moisture may also range from that normally present in the grain to approximately 17%. Pellets are hot when they leave the pellet die because of heat coming from the steam conditioning and/or the friction of being extruded through the die. Pellets should be properly cooled. As they are cooled, moisture content is also reduced. Pellets should not be stored until sufficient moisture has been removed or they will mold.
High-grain mixes should be pelleted at high heat and high moisture to achieve maximum benefits. Pelleting has been shown to improve nutrient digestibility, feed efficiency, and intake in several species. Some of the nonnutritive benefits of pelleting are less dust, ease of handling and storage, elimination of sorting of ingredients and particles by the animal, reduced segregation during handling, reduced feed wastage, and improved palatability in some cases.