Written by: Dr. Jacquie Jacob, University of Kentucky
Corn, also known as maize, is typically the cereal grain of choice for poultry feeds in the United States. For the history of corn and the different types of corn grown, refer to the publications “Specialty Corns” from New Mexico State University.
Nearly all the corn grown in the United States is hybrid. Seed is obtained by crossing inbred lines that are obtained by self-pollination through several generations. To produce hybrid seed, two inbred lines are planted together and the tassels removed from one before any pollen is shed. As a result, the kernels on the de-tasseled variety are from pollen produced on the other inbred line.
New varieties of dent corn have been developed through either conventional breeding programs or by making use of new biotechnology.
- One is a high oil corn, which, as the name implies, is higher in oil content than conventional corn. As a result, this corn has a higher energy content and a slightly higher protein content.
- Waxy corn is so-called because the endosperm is wax-like when the kernel is cut or broken open. The starch of ordinary corn is 30% amylose and 70% amylopectin, whereas the starch of waxy corn is almost entirely amylopectin. Starch structure affects the degree to which poultry can break down starch during digestion. Amylopectin is easier to digest than amylose. As a result, the digestibility of waxy starch is reported to be 10% higher than that of normal starch. Unfortunately, waxy corn tends to have less starch and more of the anti-nutritional factor beta-glucan.
- Opaque-2 corn contains higher levels of the amino acids lysine and tryptophan.
- Floury-2 corn is higher in lysine and methionine.
The opaque-2 and floury-2 varieties have improved amino acid profiles, but they do not yield as well as conventional corn and so are not widely grown.
Corn is the easiest grain for chickens to digest and is low in fiber. Yellow dent corn is the variety typically used in feed. Nutrient content of ground corn varies from variety to variety, location to location, and year to year, but recent averages suggest that corn has about 1520 kcal/lb. (3350 kcal/kg) of energy for poultry. It also has, on average, 7.5% crude protein. Corn protein is low in methionine, so in the United States, corn is typically combined with soybean meal that is higher in methionine.
Much of the phosphorus in corn grain is bound to phytate and is not readily available to birds. Birds do not produce sufficient phytase, which is the enzyme required to break down phytate and release the bound phosphorus. Phosphorus availability can be increased by the addition of the enzyme phytase to feed. Another option is to feed poultry low-phytate corn varieties (also referred to as high available phosphorus or HAP corn), which will reduce the need for supplemental phosphorus in poultry diets.
Bt-corn has been developed using new biotechnology techniques. Bt-corn is used as an alternative to spraying insecticides for control of the European and southwestern corn borer. Click here to read the article “The list that follows outlines the average nutrient content of corn:Bt-Corn: What It Is and How It Works.”
The list that follows outlines the average nutrient content of corn:
- Dry matter: 86%
- Metabolizable energy: 3373 kcal/kg (1530 kcal/lb)
- Crude protein: 7.5%
- Methionine: 0.18% (91% available)
- Cysteine: 0.18% (85% available)
- Lysine: 0.24% (81% available)
- Tryptophan: 0.07% (90% available)
- Threonine: 0.29% (84% available)
- Crude fat: 3.5%
- Crude fiber: 1.9%
- Ash: 1.1%
- Calcium: 0.01%
- Total phosphorus: 0.28%
- Available phosphorus: 0.12%
During wet milling of corn (see Table 1 below), the delivery of shelled corn is cleaned and then soaked in steep tanks. This softens the kernels. While the kernels are being soaked, nutrients are dissolved into the water. This water is later evaporated to concentrate the nutrients, resulting in the production of condensed corn fermented extractives. The remaining corn kernels are further processed to remove the germ. The germ can be further processed to remove the corn oil. The remaining portion is referred to as the corn germ meal. The wet processing of the corn kernels continues with the screening of the bran, which leaves the starch and gluten. The bran is combined with other coproducts to produce corn gluten feed. The starch and gluten slurry is then centrifuged so that the starch sinks to the bottom and the lighter gluten floats to the top. The gluten is then dried to form corn gluten meal. The starch can be further processed to produce dried corn starch for use in the food, paper, and textile industries.
The list that follows outlines the average yield of by-products from a bushel of corn (note that at 14.5% water content, a common bushel weight for corn is 48 lb.):
- Starch: 31.5 lb.
- Gluten feed: 12.5 lb.
- Gluten meal: 2.5 lb.
- Corn oil: 1.6 lb.
Corn gluten meal is a high-protein by-product of the corn milling process. It is a valuable source of methionine. Corn gluten meal also has the pigment xanthophyll, which enhances the yellow color of egg yolks. Corn gluten feed and corn germ meal are medium-value protein ingredients. Corn oil can be used as a vegetable-based energy source in poultry diets.
Nutrient content of various corn types and by-products
|High oil corn||87||3560||8.4||6.0||2.0||0.01||0.20||0.28|
|Corn germ meal (wet milled)||90||1700||20.0||1.0||12.0||0.30||0.60||0.90|
|Corn germ meal (dry milled)||91||n/a||17.7||0.9||10.9||0.03||0.43||1.10|
|Corn gluten feed||88||1750||21.0||2.0||10.0||0.20||0.50||0.60.|
|Corn gluten meal, 41%||90||3310||42.0||2.0||4.0||0.16||1.00||0.80|
|Corn gluten meal, 60%||90||3740||60||2.0||2.5||0.02||1.90||1.00|
DM = Dry matter, %; Energy = kcal/kg; CP = crude protein, %; EE = Crude fat (ether extract), %; CF = Crude fiber, %; Ca = Calcium, %; Met = Methionine, %; Lys = Lysine, %
Dry milling of corn is the process used in the manufacture of ethanol. The by-product is referred to as dried distillers grains solubles (DDGS). For more details on the use of DDGS in poultry diets, refer to the article “Formulating poultry diets with DDGS – How far can we go?” by Sally Noll of the University of Minnesota and Carl Parsons and William Dozier from the University of Illinois.