From Field to Feedlot: The Science of Grain Processing for Animal Nutrition

By Dr. Priyom Bose, Ph.D.Reviewed by Danielle Ellis, B.Sc.

Dietary nutrients play an important role in the health, growth, and yield of livestock. For instance, the milk composition and yield depend on the nutrient, energy, and protein content of the fodder fed to dairy cows. Grains are commonly fed to livestock. It is important to process grains to fulfill the nutritional demands and digestion capacity of specific livestock. Different techniques are followed to process grains for optimal outcomes.

Factors that Affect the Nutritional Benefits of Animals

Feed grains, such as corn, barley, wheat, and sorghum, contain starch as the main source of energy. The starch of feed grains is mainly composed of amylose and amylopectin at different ratios, which influence their digestion in animals. Due to varied chemical composition, the starch of waxy barley variety is less digestible than normal barley. Starch gelatinization is a grain processing method that disintegrates amylose and amylopectin chains and converts them to an easily digestible form. 

In addition to a high concentration of readily digestible carbohydrates, cereal grains also contain less digestible carbohydrates, such as cellulose. Besides starch, feed grains also contain high levels of lipids and proteins that may influence livestock digestibility. The cost of livestock feed depends on the nature and levels of different carbohydrate fractions beneficial for animals.

In a feedlot, net energy is the quantity of energy that can be digested, absorbed, and utilized by animals. This energy is predominantly used in maintaining the animal, growing body tissue, and lactation for dairy cattle. The digestibility of the feedstuff is dependent on the individual animal species and grain processing methods.

Another factor that enhances the need for grain processing need is microbial fermentation. Several microbes are present in the rumen of ruminant animals (e.g., sheep and cattle), and they can process the ingested feedstuff before they reach the small intestine, where the remnant food is enzymatically digested. 

Grains undergo microbial fermentation in the rumen. Although mammalian enzymes cannot digest fibrous carbohydrates, these are easily processed by gut microbes. This shows the importance of microbial composition and abundance in the growth, performance, and sustainability of ruminant animals.

Importance of Grain Processing for Animal Nutrition

Starch present in grains varies in its chemical composition and structure, which influences digestibility by livestock. Grain processing enables the conversion of undigestible starch form to an easily digestible one. It must be noted that the primary objective of grain processing is to enhance energy (starch) availability.

Whole grains are entire pericarp that is mostly resistant to digestion by ruminants. This is because enzymes synthesized by both rumen microbes and hosts cannot degrade the whole kernel. Grain processing involves breaking of the seed coat that would aid in digestion. For barley and oats, an additional breaking of the fibrous hull is needed to improve the digestibility.

Grain processing also enables a reduction in the particle size, which subsequently increases the surface area available for microbial colonization. This process enhances the microbial starch digestion rates and extent.

Importantly, different grain processing methods are also able to eliminate mycotoxin contamination and improve bulk management. Processed grains are commonly fed to livestock to improve meat production and lactation in cows. 

Different Grain Processing Methods

Grains are processed by application of thermal and non-thermal processes. Most feedlots select grain sources based on the cost of grain and processing. Over a period of time, different processing methods that vary in effectiveness and cost have been developed. Some of the common grain processing methods are discussed below:

Dry Processing Methods

Grinding or Milling: This method involves transforming the grain into a smaller particle size by applying pressure and searing. This is the least expensive method that is performed using hammer mills, hand stone mills, and roller mills. Grinding is an essential step for mixing, extrusion, or pelleting. Fine grinding enhances the gelatinization of starch and improves feed utilization. Fine grains are used to feed pigs and poultry; while coarsely ground grains are more favorable for ruminants. Granular particle size produced by the grinding of pelleted feeds is known as crumbles.

Dry rolling or Cracking: This process involves breaking down kernels into particles by applying pressure by moving rollers. This method achieves both breaking and crushing of the grains into particles. Cracking breaks the seed coat and the final coarse product is referred to as flaking.

Crimping: This method involves rolling of grains using corrugated rollers. This process requires pre-settings, particularly cooling during processing.

Popping and Micronizing: In this method, dry heat is applied for 15 – 30 seconds causing sudden expansion of grains and rupturing of endosperm. Rupturing of starch granules improves its digestibility. Approximately 3% of the moisture of the grain is lost during the heat treatment. Since popping reduces grain density, it enhances the need for greater storage space. This method not only enhances digestibility of starch but also improves palatability. Popping is extremely effective for sorghum and other milo grains. Although micronizing is similar to popping, it uses infrared energy instead of heat.

Roasting: This method is used to treat grains with direct flame. After roasting, the grains increase in volume and improve general digestibility. Roasting of whole soybeans causes inactivation of inhibitory factors and enhances nutritive value beneficial to poultry.

Wet Processing Methods

Soaking and reconstitution: It is the most inexpensive method which entails soaking grains in water for six to twenty-four hours. Reconstitution involves the soaking of mature, dry grains to enhance their moisture content. These processes improve the solubility of grain proteins. 

Steam rolling: Grains are exposed to steam for different periods before rolling. This process only softens the grains without any significant change in grain starch granules.

Pelleting: This is a common commercial process that combines small particles with larger ones using a combination of moisture, heat, and mechanical pressure. In this process, starch is gelatinized. Pelleting has control over granule size and density. Gelatinization improves digestibility.

Steam flaking: In this process, whole grain is exposed to steam for 10 to 40 minutes and, subsequently, rolled to varying degrees. Steam flaking involves breaking off the seed coat and gelatinizing starch to improve digestibility.

Extrusion: This is another combinational process that requires moisture, high temperature, and pressure. Extrusion causes starch gelatinization. This method prevents pathogenic infestation in feeds. 

Ensiling: This method involves partial conversion of starch to organic acid, particularly lactic acid, which helps in grain preservation. Ensiling improves microbial digestion of grain.

Chemical Processing Methods

Although chemical treatment of animal feed grain is not a popular method, two chemicals used for the same are hydroxides and formaldehyde. Grains are treated with hydroxides to reduce the resistance of endosperm and seed coat to digestion. Formaldehyde treatment protects grains against microbial attack. 

Conclusions

To determine the best grain to feed an animal, it is important to understand animal physiology and grain characteristics. For optimal gain, it is important to identify the particular type of processed grain that will aid in ruminal fermentation, host digestion, growth, productivity, and improved blood metabolites.