**2.2. Kernel structure and chemical composition**

The major structures of the wheat kernel include the pericarp (seed coat), the endosperm and the germ. The pericarp covers and protects the endosperm, which is composed of starch granules embedded in a protein matrix (about 80% of dry weight). Starch granules in the endosperm vary in size, shape and molecular structure depending on the variety and the environmental conditions of cultivation. All starches are made up of two types of glucose polymers: amylose and amylopectin. Amylose is a linear polymer with α-(1,4) glycosidic linkages and amylopectin is a branched polymer with both α-(1,4) and α-(1,6) linkages. Cereal starches are typically composed of approximately 25% amylose and 75% amylopectin. Starch digestibility in the digestive tract of animals can vary with relative proportion of amylose and amylopectin starch since the digestion of amylose is slower due to lesser accessibility of digestive enzyme compared with amylopectin.

**3. Biological characteristics**

**Table 2.** Nutrient contents (% of dry matter) of cereal grains.

**Table 3.** Variation with variety of chemical and physical characteristics of wheat.

Biological characteristics are here referred to as their digestion characteristics in the digestive tract, especially in the rumen. The quality of feed wheat is not only depending on its physical and chemical characteristics, but also depending on its biological characteristics, i.e., its rate of digestion in the rumen and potential digestibility in the total digestive tract. Among cereal grains, wheat has the most rapid rate of starch digestion in the rumen (**Figure 1**), with a rate that is almost twice that of barley and almost four times that of corn, if the grains are processed similarly. Rapid starch digestion in the rumen increases the production rate of fermentation acids, primarily the volatile fatty acids and if these accumulate, subclinical or clinical ruminal acidosis can occur. However, as with other cereal grains, whole wheat kernels are poorly digested owing to the resistance of the seed coat to attack by rumen microorganisms. Low fiber levels and a rapid rate of starch digestion make wheat more difficult to feed than most other cereal grains. The digestion rates of wheat starch vary with both inherent of kernel nature and the kernel processing including processing method used and extent of processing. The rates of wheat digestion in the rumen are commonly measured either using in vitro or in situ technique [19]. In vitro methodologies that simulate animal digestive tract conditions become vital in developing feed additive products and screening large number of feed samples at the same time. Batch culture is the one most commonly used in vitro techniques in evaluating grain digestion in the rumen [20]. The grains that are tested in batch culture need to be ground or rolled and incubated in fermentation media containing buffer and

**Item Wheat Barley Corn Oats** Organic matter 98.0 97.8 98.5 97.7 Crude protein 15.4 12.9 9.7 12.8 Neutral detergent fiber 13.3 20.5 9.3 24.0 Acid detergent fiber 3.2 6.8 3.3 16.5 Starch 70.3 58.3 75.7 58.1

Quality Assessment of Feed Wheat in Ruminant Diets http://dx.doi.org/10.5772/intechopen.75588 119

**Item Mean STD Min Max** Organic matter, % 98.5 0.15 97.1 98.7 Crude protein, % 12.6 2.9 9.3 19.1 Neutral detergent fiber, % 13.3 1.8 8.6 17.9 Acid detergent fiber, % 3.6 0.3 3.3 5.2 Ether extract, % 1.7 0.2 1.2 3.2 Starch, % 69.1 4.7 62.5 75.6

Corn and barley are two mostly used feed grains worldwide in livestock animal rations. Wheat is in general higher in protein (15.4%) than corn (9.7%) and barley (12.9%) and has starch content intermediate (70%) between corn (76%) and barley (58%) as well as lower in fiber than barley (**Table 2**). As a result, wheat has a total digestible nutrient and net energy for gain content that is comparable to corn but higher than that of barley grain [2]. However, owing to the number of different types of wheat, soft, hard and durum, the nutrient content of wheat can vary considerably. For example, on a dry matter basis, the starch content of wheat can range from 62 to 75%, protein from 9 to 19% and neutral detergent fiber from 10 to 18% (**Table 3**). This variation was most pronounced in protein content which presumably reflects the interaction between proteins and starch granules in the endosperm of wheat [15]. The high protein content of wheat may offer advantages in meeting the protein requirements of growing animals, whereas the low fiber content may contribute to its increased propensity to cause rumen acidosis. Because it exist substantial variation in the chemical composition of wheat, there is an interest in developing predictive tools to relate chemical composition to nutritional quality and animal performance [16]. Seifried et al. [17] observed negative correlation of protein content of wheat with ruminal protein degradability (r = −0.51; *P* < 0.05) and negative or positive correlation with some amino acid content. Furthermore, new developments and research in near infrared reflectance spectroscopy may allow accurate and rapid assessment of feed quality characteristics related to utilization and animal performance [18].


**Table 2.** Nutrient contents (% of dry matter) of cereal grains.

the wheat process affecting the starch damage, particle size and process quality. The grain hardness is therefore one of the important distinguishing factors in the wheat evaluation for grain quality and plays an important role with regard to the suitability of processing. Kernel hardness is measured on a scale from 0 to 35 with durum variety being the hardest (0) and soft white spring the softest (35) (**Table 1**). The increased kernel hardness is generally associated with a decrease in the rate of starch digestion, likely because the protein protects starch granules from microbial digestion. Kernel hardness could be a particularly important property as hard kernels may be more susceptible to shattering and generating the fine particles that are often associated with rumen acidosis [12] and bloat in ruminants fed high-grain diet [13]. It has been found that ruminant performance is significantly influenced by particle size of the feed consumed, and a negative relationship between feed particle size and rumen dry matter

The major structures of the wheat kernel include the pericarp (seed coat), the endosperm and the germ. The pericarp covers and protects the endosperm, which is composed of starch granules embedded in a protein matrix (about 80% of dry weight). Starch granules in the endosperm vary in size, shape and molecular structure depending on the variety and the environmental conditions of cultivation. All starches are made up of two types of glucose polymers: amylose and amylopectin. Amylose is a linear polymer with α-(1,4) glycosidic linkages and amylopectin is a branched polymer with both α-(1,4) and α-(1,6) linkages. Cereal starches are typically composed of approximately 25% amylose and 75% amylopectin. Starch digestibility in the digestive tract of animals can vary with relative proportion of amylose and amylopectin starch since the digestion of amylose is slower due to lesser accessibility of diges-

Corn and barley are two mostly used feed grains worldwide in livestock animal rations. Wheat is in general higher in protein (15.4%) than corn (9.7%) and barley (12.9%) and has starch content intermediate (70%) between corn (76%) and barley (58%) as well as lower in fiber than barley (**Table 2**). As a result, wheat has a total digestible nutrient and net energy for gain content that is comparable to corn but higher than that of barley grain [2]. However, owing to the number of different types of wheat, soft, hard and durum, the nutrient content of wheat can vary considerably. For example, on a dry matter basis, the starch content of wheat can range from 62 to 75%, protein from 9 to 19% and neutral detergent fiber from 10 to 18% (**Table 3**). This variation was most pronounced in protein content which presumably reflects the interaction between proteins and starch granules in the endosperm of wheat [15]. The high protein content of wheat may offer advantages in meeting the protein requirements of growing animals, whereas the low fiber content may contribute to its increased propensity to cause rumen acidosis. Because it exist substantial variation in the chemical composition of wheat, there is an interest in developing predictive tools to relate chemical composition to nutritional quality and animal performance [16]. Seifried et al. [17] observed negative correlation of protein content of wheat with ruminal protein degradability (r = −0.51; *P* < 0.05) and negative or positive correlation with some amino acid content. Furthermore, new developments and research in near infrared reflectance spectroscopy may allow accurate and rapid assessment of feed quality characteristics related to utilization and animal performance [18].

digestibility of grains was reported [14].

118 Global Wheat Production

tive enzyme compared with amylopectin.

**2.2. Kernel structure and chemical composition**


**Table 3.** Variation with variety of chemical and physical characteristics of wheat.
