Corn

Other Names: Maize Nutritional Characteristics:

Corn has become the standard against which other cereals, cereal by-products and other energy-yielding ingredients are compared. In most poultry diets, corn will be the major contributor of metab-olizable energy. World production is around 600 m tonnes of which 240 m tonnes are produced by the U.S.A. Although China is the world's second largest producer at around 100 m tonnes, Brazil at 40 m tonnes, is the second largest world exporter. The feed industry usually uses the equivalent of U.S.A. grade #2. As grade number increases, bulk density declines and there are greater permissible levels of damaged kernels and foreign matter allowed in the sample. Corn grade #2 should contain no more than 5% damaged kernels and 3% foreign material. While damaged kernels are unlikely to affect its energy value, foreign material is likely to reduce its energy value and hence monetary value.

Broken kernels are also potential sites for mold infestation.

The energy value of corn is contributed by the starchy endosperm, which is composed mainly of amylopectin, and the germ, which contains most of the oil. Most corn samples contain 3 - 4% oil, although newer varieties are now available which contain up to 6 -8% oil, and so contribute proportionally more energy. These high-oil corn varieties also contain 2 - 3% more protein, and proportionally more essential amino acids. The protein in corn is mainly as prolamin (zein) and as such, its amino acid profile is not ideal for poultry. This balance of amino acids, and their availability, must be seriously considered when low protein diets are formulated, because under these conditions the corn prolamin can contribute up to 50 - 60% of the diet protein. Corn is also quite high in the yellow/orange pigments, usually containing around 5 ppm xanthophylls and 0.5 ppm carotenes. These pigments ensure that corn-fed birds will have a high degree of pigments in their body fat and in egg yolks.

While #2 grade is the standard for animal feeds, lower grades are often available due to adverse growing, harvesting or storage conditions. Dependent upon the reason for lower grade, the feeding value of corn usually declines with increase in grade number. Table 2.1 shows the metabolizable energy value of corn necessarily harvested at various stages of maturity due to adverse late-season growing conditions.

Table 2.1 Corn maturity and energy value

Corn description

Moisture at harvest (%)

100 kernel wt at 10% moisture (g)

AMEn (kcal/kg) at 85% dry matter

Very immature

53

17

3014

Immature

45

22

3102

Immature

39

24

3155

Mature

31

26

3313

The energy value of corn decl i nes by 10 - 15 kcal/kg for each 1 lb reduction in bushel weight below the standard of 56 lb/bushel. However, these lower bushel weight samples show no consistent pattern with protein or levels of most amino acids, although there is an indication of loss of methionine content with the immature samples.

Another potential problem with handling immature, high-moisture corn is that the drying conditions must necessarily be harsher, or more prolonged in order to reduce moisture level to an acceptable 15%. Excessive or prolonged heating causes caramelization of corn which then has a characteristic smell and appearance, and there is concern that lysine will be less available because of Maillard Reaction with available carbohydrates.

As detailed in subsequent ingredients there is processing of corn that yields products such as gluten meal and corn oil. However, in North America well over 95% of corn is used for animal feeds.

There is some debate regarding the ideal size of ground corn particles for various classes of poultry. Within reason, the finer the grind, the better the pellet quality, while in mash diets, too fine a grind can lead to partial feed refusal. Table 2.2 indicates guidelines for expected distribution of particle sizes of corn ground to be 'fine' vs. 'coarse'. There seems to be some benefits in terms of AMEn of using a finer grind for birds up to 3 weeks of age, while a coarse grind is better for birds >21 d of age.

Depending upon the growing season and storage conditions, molds and associated myco-toxins can be a problem. Aflatoxin contamination is common with insect damaged corn grown in hot humid areas, and there is little that can be done to rectify the horrendous consequences of high levels of this mycotoxin. There is an indication of aluminosilicates partially alleviating the effects of more moderate levels of aflatoxin. If aflatoxin is even suspected as being a problem, corn samples should be screened prior to blending and mixing. Zearalenone is another mycotoxin that periodically occurs in corn. Because the toxin ties up vitamin D3, skeletal and eggshell problems can occur. With moderate levels of contamination, water-soluble D3 via the drinking water has proven beneficial.

Mold growth can be a serious problem in corn that is transported for any length of time.

With corn shipped at □ 16% moisture and subjected to □ 25°C during shipping, mold growth often occurs. One solution to the problem is to add organic acids to the corn during loading for shipments. However, it must be remembered that while organic acids will kill molds, and prevent re-infestation, they have no effect on any mycotoxins already produced.

Table 2.2 Particle size distribution of corn (%)

Particle size (microns)

Grind

Fine

Coarse

<150

5

<1

300

11

2

450

16

3

600

17

3

850

22

4

1000

16

4

1500

10

5

2000

1

10

2500

<1

24

>3000

<1

44

Damaged kernels and foreign material are going to reduce the economic value of corn. However, Dale and co-workers at Georgia suggest the energy value of these contaminants is little different from whole corn. Broken kernels were just 200 kcal/kg lower than the AMEn of corn, while foreign material tested 600 kcal/kg lower than corn. Therefore having #4 grade corn with 10% damaged kernels and 5% foreign material vs 5% and 3% respectively for #2 grade, relates to a reduction of just 25 kcal/kg for this #4 vs #2 grade corn.

If corn is to be fed in mash diets, then there seems to be an advantage to grind to as uniform a particle size as possible, (0.7 - 0.9 mm). This size is often referred to as 'medium' grind. Birds fed fine or coarse-ground corn seem to exhibit lower digestibility values. Corn presents some problems to the manufacture of pelleted diets, and often good pellet durability in diets containing □ 30% corn can only be obtained by inclusion of pellet-binders.

Gluten Free Living Secrets

Gluten Free Living Secrets

Are you sick and tired of trying every weight loss program out there and failing to see results? Or are you frustrated with not feeling as energetic as you used to despite what you eat? Perhaps you always seem to have a bit of a

Get My Free Ebook


Post a comment