**4.2. Grinding versus dry-rolling processing**

The rate and extent of dry matter digestion varies among wheat sources and with the extent of processing, but seldom have both of these properties been studied in the same experiment. A batch culture study was conducted to assess the effects of wheat grain source and processing method on dry matter and protein digestibility. Eight wheat samples collected from various sources were either ground through 2-mm sieve or dry-rolled to have processing index of 80%, and incubated for 24 h in batch culture. Dry matter digestibility ranged from 60 to 68% and from 28 to 38%, respectively, for ground and rolled wheat (**Figure 2**). The digestibility of protein varied from 52 to 62% or from 25 to 48%, respectively, for ground and rolled wheat. There was no interaction between wheat source and degree of processing. As expected, the digestibility of dry matter and protein was greater (*P* < 0.01) for ground wheat (64 and 56%) than for rolled wheat (34 and 38%) after 24 h of incubation. In vitro digestibility of dry matter and protein linearly (*P* < 0.01) increased with increasing incubation time and consistently higher (*P* < 0.01) with ground than rolled wheat, whereas no interaction between processing and incubation time was noticed (**Figure 3**). These results showed evident impact of processing method on the extent of wheat digestion in the rumen. The study also demonstrated the variation in the digestive value of commercially available wheat grain and emphasized the need to have an accurate and rapid means of quality assessment at the point of sale.

#### **4.3. Micronization processing**

**4. Processing wheat**

122 Global Wheat Production

loss of valuable starch in the manure.

**4.1. Definition of degree of processing**

**4.2. Grinding versus dry-rolling processing**

optimal processing for all kernels with a single roller setting.

Processing of cereal grains either by grinding, rolling, tempering (i.e., addition of water prior to rolling), steam-rolling (i.e., exposure to steam prior to rolling) or steam flaking (i.e., longer duration of exposure and higher grain temperature) breaks down barriers such as the hull, pericarp and protein matrix and allows microbes access to the starch harbored within endosperm. Furthermore, these processes reduce the particle size of the grain, increasing the surface area available for microbial attachment that these actions increase the rate and extent of starch digestion [25]. Although wheat has the most rapid rate of starch digestion in the rumen, whole wheat kernels are poorly digested in the rumen, and thus need to be properly processed prior to being fed to animals. In fact, excessive processing of wheat results in fine particle sizes that can cause digestive upsets (rumen acidosis, bloat) that in themselves reduce the profitability of animal production. Conversely, under processing of wheat can result in whole kernels in the diet which are not digested by rumen microorganisms contributing to a

Maintaining an optimum degree of processing that maximizes the utilization of wheat grain, and while ensuring animal health is challenging and critical to the livestock industry. The quality of the processed wheat and its particle size can be affected by kernel uniformity, test weight, kernel plumpness, and wheat variety. Kernel uniformity is a major concern for the efficiency of rolling as grain kernels vary in size and shape, making it impossible to achieve

There is no standardized measurement that has been established to assess the degree of grain processing [4]. Coarse, medium and fine are descriptors commonly used in research reports, but these terms are relative, and specific only to the treatments within a given study [26]. As a consequence, medium-processed grain referred to in one study may actually be equivalent to coarsely processed grain in another study. The need for a quantitative measurement of grain processing is evident. In the feed industry, the degree of grain processing has been described using a processing index, which refers to the volume weight (g/L) of grain after processing expressed as the percentage of its volume weight before processing [26]. This index reflects the fact that the more extensively wheat is processed, the finer the particle will be, hence, the lower the volume weight will be, and consequently, the lower the processing index. However, this processing index is influenced by the processing method used. The values generated with dry-rolling can differ substantially, depending on the hardness of wheat kernels, whereas, temper- or steam-rolling make fractured particles that are more likely to adhere together contributing to reduced fines.

The rate and extent of dry matter digestion varies among wheat sources and with the extent of processing, but seldom have both of these properties been studied in the same experiment. A batch culture study was conducted to assess the effects of wheat grain source and processing Micronization is a dry-heat process that generates infrared electromagnetic short waves to heat the feedstuff to approximately 110–115°C. It has been used to process grains to increase their utilization [27]. Rapid internal heating is accompanied by a rise in water vapor pressure that the feedstuff is cooked from the inside out and the kernel expands to the point of eversion. This process has been widely used to process grains for livestock consumption [28]. Wang et al. [29] reported that the micronization reduced the in situ dry matter digestibility of both full-fat canola seed and flaxseed. McAllister and Sultana [19] compared three different wheats varying with kernel hardness (i.e., soft, hard and durum) and found that in situ digestibility of dry matter, crude protein and starch were reduced by micronization processing in all three types of wheat. However, the reductions were greater with soft than

**Figure 2.** Effects of processing and wheat source on in vitro rumen dry matter and protein digestibility. For dry matter digestibility, SEM = 2.9%, processing (*P* < 0.01), wheat (*P* < 0.20) and process x wheat (*P* < 0.45). For crude protein digestibility, SEM = 4.7%, processing (*P* < 0.01), wheat (*P* < 0.01) and process x wheat (*P* < 0.19).

yield, back fat thickness, and rib eye area. The greater feed intake but lower feed efficiency for steers fed with coarsely processed wheat may be resulted from an increased an amount of unprocessed whole kernel, in particularly when the uniformity of kernel size is poor and rollers are set to roll the large kernels [32]. The unprocessed wheat kernel is often poorly digested in the digestive tract of cattle because of the seed coat protection from microbial and host enzyme access and its faster passage through the digestive tract as well. Consequently, the digestibility of coarsely processed wheat would be lower and thus animals need to increase feed intake to meet their nutrient requirement. These results appeared to contrast to the general recommendation that wheat should be coarsely processed with processing index of 80 to 85%. The increased feed intake by steers fed wheat with 85% of processing index would contribute to the adverse effects on feed efficiency and risks of liver abscesses. The optimum

Quality Assessment of Feed Wheat in Ruminant Diets http://dx.doi.org/10.5772/intechopen.75588 125

Wheat grain is generally recommended to be fed to ruminants in combination with more fibrous or slowly fermented feed grains and limited to 40 or 50% of the diet (dry matter basis) because of its rapidly fermentable starch in the rumen. A study using rumen cannulated beef heifers was conducted to compare inclusion level of wheat relative to barley grain in finishing beef cattle rations on measuring rumen pH and fermentation, and digestibility if nutrients in the total digestive tract [33]. In this study wheat was substituted for barley grain at 0, 30, 60, or 90% of the diet dry matter with the remainder of the diet composed of 6% barley silage and 4% vitamin and mineral supplement. All grains were dry-rolled to a processing index of 80%. Increasing wheat level from 30, 60 to 90% in the diet linearly increased the duration of time that rumen pH was under 5.8, but ruminal pH below 5.5 and 5.2 were not affected. These results indicated that subclinical rumen acidosis was not exacerbated with increase of wheat grain up to 90%. Rumen acidosis includes acute acidosis and subacute acidosis (also called subclinical rumen acidosis). The acute acidosis is characterized by sustained low pH (<5.2) without recovery unless intervention is used [12]. The subacute rumen acidosis occurs in repeated bouts where pH is <5.6 for >3 h per day [34], but unlike the situation for acute acidosis, the pH recovers between bouts. The subacute rumen acidosis is a common metabolic disorder in animals fed high-grain diet with rapid fermentation of feed in the rumen and subsequent accumulation of volatile fatty acids (acetate, propionate, butyrate), whereas acute acidosis is caused by accumulation of lactic acid in the rumen and much less happen. Feed intake, animal performance and feed efficiency are adversely impacted when animals suffer from subacute rumen acidosis [12]. However, there was no effect of feeding increasing levels of wheat on rumen fermentation and nutrient digestibility, which suggest that the levels of wheat included in finishing diets of beef cattle could be higher than typically used in the feed-

processing index may depend on starch content of the wheat as well [16].

lot industry if proper bunk management and processing are employed.

Grain hardness is a trait that has been used for decades by the wheat industry to differentiate quality and market classes, and it is characterized as the resistance of the kernel to fracture [35].

**4.6. Impact of wheat type on feed value**

**4.5. Level of wheat in the diet**

**Figure 3.** Effects of processing and incubation time on in vitro rumen dry matter and protein digestibility. For dry matter digestibility, SEM = 1.1%, processing (*P* < 0.01), incubation time (*P* < 0.01) and process x incubation time (*P* < 0.68). For crude protein digestibility, SEM = 2.3%, processing (*P* < 0.01), wheat (*P* < 0.01) and process x wheat (*P* < 0.79).

hard wheat varieties. These authors suggested that the micronization altered the properties of the endosperm in soft wheat that may be more closely resembles that of the harder wheat. The micronization may also change wheat starch that may be related to the nature of the endosperm with alterations of proteins within the fibrillin complex [30]. The reduction of rate and extent of wheat starch digestion using micronization method may provide an effective processing technique to modulate the rate of acid production during the fermentation of wheat in the rumen, thus reduce the severity of rumen acidosis.

#### **4.4. Impact of degree of processing on the feed value of wheat**

Recently, a series of experiments using beef cattle were conducted in our laboratory at the Lethbridge Research and Development Centre to determine the maximum level of wheat grain that could be included in finishing cattle rations, the effects of degree of grain processing on wheat utilization and comparison the feeding value between hard versus soft wheat. A study was conducted to compare inclusion of 90% wheat grain processed to processing index of either 75 or 85% on the growth performance of finishing beef cattle [31]. Compared to steers fed dry-rolled wheat with a processing index of 75%, steers fed wheat with a processing index of 85% ate 0.4 kg per day more feed. However, this difference in feed intake did not alter the daily gain or final live weight of steers. As a result, the feed efficiency, expressed as daily per unit of feed consumption, of steers fed wheat with a processing index of 85% was lower than for steers fed wheat with a processing index of 75%. Carcass traits had a trend to be different with higher back fat thickness but lower rib eye area and lower quality grade (% Canada AAA) for steers fed wheat with a processing index of 85% than with a processing index of 75%. The steers fed wheat with a processing index of 85% also had more numbers of liver abscesses. Therefore, a high processing index (85%, i.e., coarsely processed) increased feed consumption but reduced feed efficiency and adversely impacted carcass quality, including saleable meat yield, back fat thickness, and rib eye area. The greater feed intake but lower feed efficiency for steers fed with coarsely processed wheat may be resulted from an increased an amount of unprocessed whole kernel, in particularly when the uniformity of kernel size is poor and rollers are set to roll the large kernels [32]. The unprocessed wheat kernel is often poorly digested in the digestive tract of cattle because of the seed coat protection from microbial and host enzyme access and its faster passage through the digestive tract as well. Consequently, the digestibility of coarsely processed wheat would be lower and thus animals need to increase feed intake to meet their nutrient requirement. These results appeared to contrast to the general recommendation that wheat should be coarsely processed with processing index of 80 to 85%. The increased feed intake by steers fed wheat with 85% of processing index would contribute to the adverse effects on feed efficiency and risks of liver abscesses. The optimum processing index may depend on starch content of the wheat as well [16].
