**3. Biological characteristics**

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

**Figure 1.** Rumen fermentability of feeds that are commonly fed to ruminants, the highest is wheat grain and lowest is straw.

rumen inoculum at 39°C under anaerobic condition over a period of up to 48 h of incubation. The data that are generated can be used to determine the kinetic parameters of fermentation including the rate and extent of the grain digestion. The in situ techniques have been extensively used for measuring rumen digestion of feeds as well. The dynamic interactions within the rumen are difficult to simulate in vitro, and thus the in situ techniques study digestion within the rumen itself and reduce the need for ruminal simulation. Current nutrition models need for quantitative information on rates and extents of feed digestion in the rumen. The in situ rumen digestion kinetics of grains are measured by filling processed grain in bags and incubated in the rumen via rumen cannula for a period of series times, thus rumen cannulated animals are required.

Rumen digestion kinetics of wheat grain also varies with wheat genotypes. Seifried et al. [17] measured in situ rumen digestion kinetics of over 20 wheat samples varying with genotypes and found considerable variation in digestion kinetics of dry matter, protein and starch among wheat genotypes. The digestion kinetics parameters include soluble fraction which is immediately digestible, potential digestible fraction and rate of digestion. The soluble fraction ranged from 21 to 40% for dry matter, 11 to 22% for protein and 25 to 49% for starch; the potential digestible fraction varied between 53 to 71% for dry matter, 51 to 74% for starch and 75 to 89% for protein; and the digestion rate ranged from 29 to 54%/h for dry matter, from 18 to 27%/h for protein and from 38 to 99%/h for starch [17]. The differences in digestion kinetics among genotypes were explained by the variation in the endosperm characteristics [22]. Therefore, these authors concluded that selection of wheat grains with slower digested wheat can be used to shift starch digestion from the rumen to the small intestine. The potential to shift more starch digestion from the rumen to the small intestine by developing lower ruminal digested wheat will be beneficial to reduce risks of rumen acidosis and improve energy efficiency, in particularly for ruminants fed high-grain rations. It is known better energy efficiency with starch digested in the small intestine than in the rumen [23, 24]. However, although improving wheat as a feed grain by selection of slower rate of digestion in the rumen is a wise consideration for wheat breeder, it may be challenging as all types of wheat (soft, hard and durum) examined in the study of McAllister and Sultana [19] exhibited rapid digestion rates than that of corn.

Kinetics of nutrient digestions were estimated using the model: y = a + b(1 − e−c(t−lag)), a = soluble fraction; b = slowly digestible fraction; c = fractional digestion rate constant at which b is digested; lag = lag time (h), and t = time of incubation (h). Effective degradability (ED) = a + bc/(c + k), where k is the ruminal flow rate assuming 0.06/h. a,b,c means within a

**Kinetics parameters Item a b c ED, %**

Quality Assessment of Feed Wheat in Ruminant Diets http://dx.doi.org/10.5772/intechopen.75588 121

Durum 0.123a 0.756 0.041 43.0b Red spring 0.121a 0.736 0.044 43.2b Soft red winter 0.097b 0.720 0.062 46.3a

Durum 0.081a 0.857 0.035 39.7 Red spring 0.027b 0.837 0.051 41.2 Soft red winter 0.008c 0.868 0.053 41.5

Durum 0.173b 0.783 0.039b 48.2b Red spring 0.243a 0.738 0.043b 55.1a Soft red winter 0.104c 0.744 0.060a 47.6b

column and within a nutrient, with different letters differ (*P* ≤ 0.05).

**Table 4.** Variation with variety of in situ rumen digestion kinetics of wheat.

*Dry matter*

*Protein*

*Starch*

The rates of wheat dry matter or starch digestion in the rumen varied with type of wheat. McAllister and Sultana [19] measured in situ rumen digestion kinetics of three different wheats (i.e., soft, hard and very hard) with same degree of processing (**Table 4**). These authors found that the rates of dry matter digestion were lowest for durum (4.1%/h) and highest for soft wheat. The digestion rates of wheat in the rumen appeared to be associated with kernel hardness because the kernel hardness can reflect to relative affinity between protein and starch in the endosperm [15]. It suggests that the nature of endosperm protein may influence rumen digestion of wheat. However, Lanzas et al. [21] reported the variation in the fermentation kinetics among wheat samples from various sources, did not attribute to any chemical parameters. Whereas, the study by Lanzas et al. [21] focused mainly on the impact of kernel processing that may confound with chemical effects on the fermentation dynamics of wheat. In fact, it was reported that protein content of wheat was most highly correlated with the rate of wheat digestion (r<sup>2</sup> = −0.77) in the study by McAllister and Sultana [19]. It suggests protein characteristics as a factor that influences the digestive properties of wheat in the rumen. This phenomenon could be explained by the nature of wheat protein. Wheat grain has two major proteins, puroindolines A and B that are associated with the fibrillin protein complex on the surface of wheat starch granules which may have a central role in determining the digestion rate of wheat starch [22].


Kinetics of nutrient digestions were estimated using the model: y = a + b(1 − e−c(t−lag)), a = soluble fraction; b = slowly digestible fraction; c = fractional digestion rate constant at which b is digested; lag = lag time (h), and t = time of incubation (h). Effective degradability (ED) = a + bc/(c + k), where k is the ruminal flow rate assuming 0.06/h. a,b,c means within a column and within a nutrient, with different letters differ (*P* ≤ 0.05).

**Table 4.** Variation with variety of in situ rumen digestion kinetics of wheat.

rumen inoculum at 39°C under anaerobic condition over a period of up to 48 h of incubation. The data that are generated can be used to determine the kinetic parameters of fermentation including the rate and extent of the grain digestion. The in situ techniques have been extensively used for measuring rumen digestion of feeds as well. The dynamic interactions within the rumen are difficult to simulate in vitro, and thus the in situ techniques study digestion within the rumen itself and reduce the need for ruminal simulation. Current nutrition models need for quantitative information on rates and extents of feed digestion in the rumen. The in situ rumen digestion kinetics of grains are measured by filling processed grain in bags and incubated in the rumen via rumen cannula for a period of series times, thus rumen

**Figure 1.** Rumen fermentability of feeds that are commonly fed to ruminants, the highest is wheat grain and lowest is straw.

The rates of wheat dry matter or starch digestion in the rumen varied with type of wheat. McAllister and Sultana [19] measured in situ rumen digestion kinetics of three different wheats (i.e., soft, hard and very hard) with same degree of processing (**Table 4**). These authors found that the rates of dry matter digestion were lowest for durum (4.1%/h) and highest for soft wheat. The digestion rates of wheat in the rumen appeared to be associated with kernel hardness because the kernel hardness can reflect to relative affinity between protein and starch in the endosperm [15]. It suggests that the nature of endosperm protein may influence rumen digestion of wheat. However, Lanzas et al. [21] reported the variation in the fermentation kinetics among wheat samples from various sources, did not attribute to any chemical parameters. Whereas, the study by Lanzas et al. [21] focused mainly on the impact of kernel processing that may confound with chemical effects on the fermentation dynamics of wheat. In fact, it was reported that protein content of wheat was most highly correlated with the rate of wheat digestion (r<sup>2</sup> = −0.77) in the study by McAllister and Sultana [19]. It suggests protein characteristics as a factor that influences the digestive properties of wheat in the rumen. This phenomenon could be explained by the nature of wheat protein. Wheat grain has two major proteins, puroindolines A and B that are associated with the fibrillin protein complex on the surface of wheat starch granules which may have a central role in

cannulated animals are required.

120 Global Wheat Production

determining the digestion rate of wheat starch [22].

Rumen digestion kinetics of wheat grain also varies with wheat genotypes. Seifried et al. [17] measured in situ rumen digestion kinetics of over 20 wheat samples varying with genotypes and found considerable variation in digestion kinetics of dry matter, protein and starch among wheat genotypes. The digestion kinetics parameters include soluble fraction which is immediately digestible, potential digestible fraction and rate of digestion. The soluble fraction ranged from 21 to 40% for dry matter, 11 to 22% for protein and 25 to 49% for starch; the potential digestible fraction varied between 53 to 71% for dry matter, 51 to 74% for starch and 75 to 89% for protein; and the digestion rate ranged from 29 to 54%/h for dry matter, from 18 to 27%/h for protein and from 38 to 99%/h for starch [17]. The differences in digestion kinetics among genotypes were explained by the variation in the endosperm characteristics [22]. Therefore, these authors concluded that selection of wheat grains with slower digested wheat can be used to shift starch digestion from the rumen to the small intestine. The potential to shift more starch digestion from the rumen to the small intestine by developing lower ruminal digested wheat will be beneficial to reduce risks of rumen acidosis and improve energy efficiency, in particularly for ruminants fed high-grain rations. It is known better energy efficiency with starch digested in the small intestine than in the rumen [23, 24]. However, although improving wheat as a feed grain by selection of slower rate of digestion in the rumen is a wise consideration for wheat breeder, it may be challenging as all types of wheat (soft, hard and durum) examined in the study of McAllister and Sultana [19] exhibited rapid digestion rates than that of corn.
