Written by: Dr. Jacquie Jacob, University of Kentucky
Cereals are grasses that produce edible starchy grains, many of which can be used in poultry diets as an energy source. Although the starch in corn is highly digestible, most of the other grains contain anti-nutritional factors that interfere with digestion and/or the absorption of nutrients. These antinutritional factors include the nonstarch polysaccharides, often referred to as NSPs. NSPs cannot be broken down by the digestive enzymes poultry normally secrete in the small intestine (referred to as endogenous enzymes). As a result, the NSPs gel, increasing the viscosity of the intestinal contents. The increased intestinal viscosity reduces the availability of the nutrients in the feed. In addition, the presence of NSPs typically results in sticky droppings, which increase the moisture content of the litter. Litter that has a high moisture content can adversely affect air quality within the poultry house.
Amaranth is an ancient crop that has been grown for thousands of years. The grain was a staple in the diet of the Aztecs. The crop has recently been “rediscovered” and has potential as a food and as a feed ingredient.
Barley is commonly used in poultry diets in some regions of Canada and Europe. This cereal is grown on areas of both irrigated and dry land in the United States. It is an early-maturing crop that offers agronomic advantages when used in crop rotation. Barley is considered a medium-energy grain. It has a low starch content, a high fiber content, and some antinutritional factors.
Buckwheat is often grouped with the cereals, but it is actually not a cereal. It has a cereal-like fruit seed that is related more closely to rhubarb than to cereals. It is often referred to as a pseudo-cereal. Buckwheat is a summer annual that has a potential role in organic crop production.
Corn, also called maize, is native to the Americas and was first cultivated by the American Indians. The corn plant is efficient at converting large amounts of sunlight into stable forms of chemical energy stored as starch, cellulose, and oil. Corn is the grain most routinely used in commercial poultry diets in the United States because it has a good energy content and is easy to digest. The amino acid profile of the protein in corn complements the amino acid profile of the other ingredients, such as soybean meal, typically used in feed. Alternative grains are typically evaluated in relation to corn.
Oats are more tolerant of wet weather and acidic soils than wheat or barley. Oats also require less agrochemical and fertilizer input. There has been renewed interest in oats as a feed ingredient.
Pearl millet is typically resistant to drought and heat, so it is grown widely in tropical regions of Africa and Asia. Some pearl millet is also grown in the United States.
Quinoa (pronounced KEEN-wa) is a pseudo-cereal grown for its edible seeds. It is not a member of the grass family (and therefore is not a cereal) and is more closely related to species such as beets and spinach.
Rice bran is high in fiber and low in energy. Rice bran also contains the antinutritional factor trypsin inhibitor. As a result, it is recommended that rice bran make up no more than 10% to 15% of the total content of a poultry diet.
Rye is a versatile crop. It can be grown as forage for cattle and other ruminant livestock or as green manure in crop rotations in organic farming. It can also be grown for grain that can be used as a feed ingredient, for alcohol distillation, or for human consumption.
Sorghum (also called milo and guinea corn) is a highly drought-resistant crop that is grown in many areas of the world, including the United States. Sorghum is only 3% to 5% lower in feeding value than corn. It is often less expensive than yellow corn. The level of tannins in sorghum limit its use in poultry diets. However, tannin-free varieties are now available, and as a result, sorghum can be substituted for corn in poultry diets with only minor changes in the amounts of other ingredients.
Spelt is an ancient wheat species that shows a higher resistance to environmental influences than common wheat.
Triticale is a hybrid developed by crossing wheat and rye. It is reported to grow well in regions not suitable for corn or wheat.
Wheat is often used in poultry diets in western Canada and parts of Europe. The husk of wheat detaches from the grain during threshing (unlike conventional barley and oats where the husk remains attached) reducing its fiber content.
Many of the cereal grains used as animal feed are also used for human consumption or the development of industrial products. The grains are cleaned and then either dry or wet milled. Dry milling removes the outer fibrous coating of the seed and is used in the production of flour. Wet milling is used in the production of sugar, starch, syrup and/or oil. Many of the by-products of both dry and wet milling are suitable for inclusion in poultry feeds.
Understanding the by-products generated by dry and wet milling requires a basic understanding of the parts of the cereal grain. All grains have four basic parts: seed coat, aleurone, endosperm, and germ.
The seed coat can exist in the form of a hull. For those cereals without a hull, the seed coat is in the form of the pericarp. The function of the seed coat is to protect the grain from moisture, insects, and fungal infection. The seed coat must be broken to allow for the digestion of the nutrients contained within the seed. The seed coat does not supply nutritional value, but depending on the particular type of cereal, the seed coat can dilute the amount of starch in the diet. In oat grains, for example, the hull represents 25% of the seed (on a dry matter basis). In sorghum, however, the seed coat represents only 3% to 6% of the grain weight and has little effect on the nutritional value of the grain.
The aleurone is a layer surrounding the endosperm. The endosperm is the location of most of the starch, which provides energy to the animals consuming it and is also the source of flour. The aleurone contains fiber and protein. The germ is the embryo of the seed and the location of protein and oil.
Common cereal by-products
- Grain hulls are the outer covering of the grain seed. The most common hulls are from oats and rice milling. Grain hulls are low in energy and crude protein but high in crude fiber. Hulls are typically classified as roughage and not widely used in feeds for poultry that require growth or high production.
- Bran is the coarse outer covering of a seed. It also contains a little of the flour. The most common brans are corn, rice, and wheat. Nutritionally, bran contains fiber and protein.
- The germ is the embryo of the seed. Germ meal is high in lipids and protein. The most common feed germ meals are derived from corn and wheat.
- Gluten feed and gluten meal are by-products of wet milling. Gluten is the substance remaining after removal of the germ and the starchy endosperm. Gluten feed and meal are considered protein sources. The most common cereals used in gluten feed and meal are corn and sorghum.
- Middlings (also referred to as midds) are by-products from the production of flour. They include the bran, shorts, germ, flour, and tailings. Rye and wheat are the most common middlings available. The maximum allowed levels of crude fiber in rye and wheat middlings are 8.5% and 9.5%, respectively.
- Grain screenings are a mixture of different materials that contain a minimum grain content of 70% and a maximum ash content of 6.5%. Grain screenings can include various combinations of dust, chaff, weed seeds, broken grains, unsound grains, and any other materials separated during the cleaning and processing of the grain. Mixed screenings must contain no more than 27% crude fiber and 15% ash.
- Groats are the grain seeds without the hull. The most common are oat and rice groats. Groats have a relatively low crude fiber content and contain a higher percentage of protein than the original grain.
- Mill run (also known as mill by-product) consists of bran, shorts, germ, flour, and tailings. It is a by-product of most of the cereal grains. There are specific minimum crude fat and maximum crude fiber limits that mill runs can contain, and these requirements vary depending on the cereal grain involved.
- Corn hominy feed includes corn bran, germ, and flour. It contains a higher percentage of both crude protein and fiber than the original corn grain. Compared to other by-products, however, corn hominy feed is lower in crude fiber content. Hominy feed must contain at least 4% crude fat.
- Barley malt sprouts are by-products from the malting industry. They are classified as a protein source and must contain a minimum of 24% crude protein. Malt sprouts consist of roots, sprouts, and malt hulls.
- Rice polishings, as the name suggests, are the residue created when polishing to produce white rice (versus brown rice). Rice polishings are low in crude fiber are high in crude fat and are a good source of the vitamin thiamin.
- Wheat red dog is a by-product of milling wheat and includes tailings with some bran, germ, and flour. The maximum allowed fiber content is 4%.
- Wheat shorts are also a by-product of wheat milling and consist of bran, germ, flour, and tailings. The maximum crude fiber content for shorts is 7%.