Common feedstuffs must undergo processing to ensure the best use in swine diets. Processing may alter the physical or chemical nature of the nutrients, allow more uniform mixing of ingredients, or reduce wastage of feed by the pig. This may improve feed intake or digestion and absorption of feed nutrients. The result should be economical improvements in rate of gain or feed efficiency.
Grains and other feed ingredients may be processed in many ways. Grinding is the most common. In recent years, the use of rolling, roasting, and extruding have increased. High moisture processing and pelleting are also used in processing swine feeds.
Grinding
Grinding with a hammer mill is the most common method of processing grains. Grinding improves the feeding value of most grains. It also improves the mixing qualities of grains and assures intake of a balance of diet ingredients. The initial cost of a hammer mill is lower than most other processing methods, even though the cost of operation may be higher.
Different feedstuffs require various degrees of grinding (fine, medium, coarse). A finer grind can improve feed efficiency in corn and grain sorghum but very fine grinding may lead to gastric ulcers. Fine grinding of wheat results in a powdery, dusty diet that is very undesirable. Performance of growing and finishing pigs fed coarse ground wheat is superior to those fed fine ground wheat.
The particle size of a grain processed in a hammer mill depends on three factors. The size of the openings in a hammer mill screen will partially determine particle size. The speed of the hammer mill also affects particle size. Particle size increases as rpm is decreased and as the flow of grain into the mill increases. For most grains, screen opening diameters in the range of 1/8 to 3/8 inches will provide proper grinding.
Rolling
Roller mills may be used to:
Processing grains with a roller mill may produce a product similar to grinding but results in a more uniform final product. Roller mills are generally more expensive than hammer mills but cost less to operate. Because of the added cost of steam, dry-rolling is typically more economical than steam-rolling or steam-flaking for most diets.
Rolling is the best processing for wheat and oats under most situations. Very lightly rolled (crushed) wheat appears to improve feed intake and gains compared to ground wheat when fed to pigs over 40 pounds. Rolled oats are desirable in some baby pig diets.
Roasting And Extruding
Roasting and extruding are used primarily to process soybeans. Raw soybeans contain toxic compounds that reduce pig performance. Soybeans must be heated to destroy these compounds. The ideal cooking time and temperature depends on the equipment and moisture content of the soybeans. Heating soybeans at 270 degrees to 300 degrees F for 2 to 5 minutes to an exit temperature of 245 degrees F (240 degrees to 260 degrees F is acceptable) is adequate to destroy the toxins in soybeans.
Roasters use an external source of heat, usually gas. Extruders use heat generated by the soybean kernel. Extruders subject soybeans to extremely high pressure, creating heat. An exterior source of heat is often used as a precaution. Both methods do an adequate job of processing soybeans. The availability of amino acids is similar, as is the performance of pigs fed extruded or roasted soybeans. Roasters are usually less expensive than extruders but may cost more to operate.
Some data suggest an improvement in pig performance from roasting grains (corn, grain sorghum). Before purchasing a roaster for grain processing, however, the improved performance must offset the cost of processing.
Pelleting
Researchers do not completely agree on the benefits of pelleting swine diets. Improvements in feed efficiency range from 3 to 10 percent with a 5 percent improvement being a reasonable standard. Improved digestibility of nutrients and reduced feed wastage account for the improved efficiency. Improvements in rate of growth from pelleting of diets have been inconsistent but may be as much as 3 to 6 percent. Pellet size and quality (firmness) may determine if pelleting feed is a viable option. A firm 3/16 inch pellet appears to be ideal for growing and finishing pigs. Small pellets or crumbling of large pellets may result in greater intake of baby pig diets. Greater advantages of pelleting appear to result when using certain diet ingredients (barley, wheat middlings, etc.).
High Moisture Processing
High moisture processing has limited benefits from a strict nutritional viewpoint. High moisture grains show slight advantages in phosphorus availability and protein digestibility. Higher processing and storage costs must be offset by improved harvesting efficiency and elimination of grain drying costs. High moisture-harvested grains must be ground or rolled before mixing and feeding.
Other Processing Methods
A number of other processing methods have limited applications to swine
diets because of lowered effectiveness or higher costs. Among these methods
are micronizing, popping, and exploding.