The process of manufacturing animal feed involves converting raw materials with widely varying physical, chemical, and nutritional compositions into a homogeneous mixture. This mixture is suitable for producing the desired nutritional response in animals.
The process is primarily physical, with few chemical changes. It is important to note that some raw materials undergo extensive processing before inclusion in the mixed feed.
For example, oilseeds may undergo oil extraction by solvent or mechanical methods, and beans such as soybeans may be heat-treated to denature anti-nutritive factors. Additionally, fishmeal and meat meal undergo their own production processes.
The feed manufacturing process can be broken down into several key operations, which generally include:
- Raw material storage and selection.
- Raw material weighing.
- Raw material grinding.
- Mixing of dry ingredients and addition of liquids.
- Pelleting of mixed feed (optional).
- Blended feed bagging, storage, and dispatch.
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Stages in the Feed Manufacturing Process
Depending on the type of feed, the manufacturing process typically begins with the grinding of raw materials. This step is critical for producing particle sizes that can be easily and optimally accepted by animals.
Depending on the feed formulation, it may contain up to 10 different components, including carbohydrates, proteins, vitamins, minerals, and additives. The feed ration can be pelleted by proportionally homogenizing these specific components. Pelleting is commonly achieved through extrusion.
Maintaining a hygienic environment throughout the feed production process is essential for ensuring the quality of the feed. Factors considered during feed formulation include the age and production level of the animal, species, and the cost of the feed. Nutritional levels are optimized using methods such as the Pearson Square or computer software like WinFeed.
After formulation, some feeds are further processed into pellets through either hot or cold methods. Pellets are formed using pelletization or extrusion technologies. Proteins and starch make up a significant portion of these formulations. Proteins consist of amino acids linked by peptide bonds, while starch is a polymer of amylose and amylopectin, connected by hydrogen and glycosidic bridges.
Monogastric animals, such as poultry, swine, and fish, rely on enzymatic hydrolysis in the fore stomach to break down complex food components. However, this process may not always be efficient, leading to reduced nutrient absorption, which impairs growth and performance. Consequently, further processing of the raw formulated mash becomes necessary.
Types of Feed Processing Methods
1. Cold Processing: Cold processing methods involve processing feeds at or below ambient temperatures. This includes grinding in hammer mills, size reduction, soaking, and reconstitution of dried feeds. These methods mainly affect the physical appearance of the feed, with minimal to no changes in its chemical properties. Feeds produced through cold processing are typically in mash form.
2. Hot Processing: Hot processing applies heat to animal feeds to improve hygiene, nutritional quality, and physicochemical properties. This involves applying thermal energy to dry or wet ingredients, such as soybeans or cereals, to soften seeds, modify starches, or denature anti-nutritional factors like trypsin inhibitors.
Common hot processing methods include steam rolling, roasting, and steam flaking. Steam flaking differs from steam rolling due to the higher moisture content and extended contact time, increasing starch digestibility by 22.7% to 51.2%. As a result, these feeds enhance the performance of animals.
3. Popping: Popping is a dry, hot feed processing method used on seeds. This method causes the endosperm of seeds to rupture suddenly, after which the seeds are rolled before being fed to animals.
4. Pelletization: Pelletization is another hot processing method. It involves grinding and formulating feed, which is then forced through a thick, spinning die using rollers. Feeds can be produced in various diameters, lengths, and hardness levels.
This process alters the physicochemical properties of the feed due to the high pressure involved. Pelleting minimizes losses during feeding and transportation, as pellets are less prone to breakage. Growth rate and feed efficiency have been shown to increase by 6.6% to 7.9% due to pelleting.
5. Extrusion Processing: Extrusion technology operates on three main principles: steam conditioning, high-temperature cooking, and high-shear pressure. The process begins with the formulation and tempering of the mixture to about 30 percent moisture content.
Steam conditioning, the first step in this method, aims to facilitate die lubrication and feed particle adhesion. This process increases pellet durability index and gelatinizes starch. Broilers fed extruded pellets have a higher feed intake, leading to increased live weight gain compared to those fed mash.
Extrusion combines moisture, high temperature, and pressure to modify starch and protein, thereby enhancing their digestibility.
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Benefits of Extrusion Processing
There has been improved performance in swine, fish, and poultry fed extruded pellets compared to those fed mash. The better performance can be attributed to:
- The heat used during feed conditioning breaks down starch into its constituent monomers, which are further broken down into monosaccharides. Proteins are broken down into smaller polypeptides, enhancing feed digestibility due to the larger surface area exposed to enzymatic hydrolysis.
- During pelleting, nutrients tend to concentrate in the product, and pellets are bound together. This minimizes wastage during feeding and transportation, leading to increased average daily gain.
- Energy digestibility in cereal-based diets is improved due to starch gelatinization, resulting in better performance of early-weaned pigs fed extruded feeds.
- Improved fecal digestibility of some amino acids in chickens is observed.
- Extrusion increases the digestibility of proteins, amino acids, and nitrogen by denaturing proteins and modifying the side chains of amino acids. The combination of starch gelatinization and these protein changes results in better digestibility, increased feed intake, improved feed conversion ratio, and enhanced performance in chickens.
Extrusion leads to starch gelatinization, making it more susceptible to amylase, which further improves starch digestibility and poultry performance.
Grain Milling for Feed Preparation
Cereal grains such as corn, sorghum, wheat, and barley are commonly used in the preparation of feed for livestock, poultry, swine, and fish. Roller and hammer mills are the two main types of equipment used to grind grains into smaller particle sizes. The milling process involves mechanical actions such as compression, shearing, crushing, cutting, friction, and collision.
The particle size of ground cereals is critical in animal feed production. Smaller particle sizes increase the number of particles and the surface area per unit volume, which enhances access to digestive enzymes. Other benefits include easier handling and mixing of ingredients.
The average particle size is measured as the geometric mean diameter (GMD), expressed in millimeters (mm) or microns (μm), while the range of variation is described by the geometric standard deviation (GSD). A larger GSD represents lower uniformity. According to Lucas (2004), GMD and GSD are accurate descriptors of particle size distribution when expressed as log data, as particle sizes are generally log-normally distributed.
Studies show that grinding different grains with the same mill under similar conditions results in products with different particle sizes. The hardness of a grain sample is related to the percentage of fine particles obtained after grinding, with lower hardness grains yielding a higher percentage of fine particles.
Rose et al. (2001) explained that hard endosperm produces irregularly-shaped larger particles, while soft endosperm produces smaller particles.
The correlation between particle size and energy consumption is not always positive. Obtaining very fine particle sizes requires more energy, which reduces the production rate.
This article has examined the classification of raw materials and the methods of sourcing these raw materials used in feed milling processes. The role of extrusion technology and grain milling has been highlighted, emphasizing their impact on improving animal feed digestibility and performance.
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