When making feeds, manufacturers consider the age, production level of the animal, species and the cost of the feed.
They then play around with figures using Pearson Square method or a computer software such as Win feed to attain the optimal theoretical nutritional levels of the formulated mash.
After formulation, some feeds are further processed into pellets by either hot or cold processing. Pellets are either formed using pelletisation or extrusion technologies. Proteins and starch forms a larger percentage of these formulations. Proteins are made up of amino acids as building blocks joined together by peptide bonds.
On the other hand, starch is a polymer of amylose and amylopectin monomers having both hydrogen and glycosidic bridges.
Poultry, swine and fish are monogastrics (have single-chambered stomach), therefore, rely on enzymatic hydrolysis of complex food components in the fore stomach. Sometimes these feeds are not effectively hydrolysed. This reduces their absorbability, impairing both the growth rate and performance of animals. Therefore, further processing of the raw formulated mash is necessary.
Manufacturers use different processing method namely:
Feeds are processed at or lower than the ambient temperature. These processes include grinding in the hammer mill, size reduction, soaking and reconstitution of dried feeds. These processes mostly influence the physical appearance of the feeds but less or no, modification on the chemical properties of the feeds. Feeds under these categories are the mash forms.
Heat treatment is applied to animal feeds to improve hygiene, nutritional quality and physic-chemical properties. Thermal energy is applied to either dry or wet ingredients such as soybeans or cereals. The aim here is to soften the seeds, modify the starch or denature the anti-nutrients such as trypsin inhibitors.
This procedure is common in steam rolling, roasting and steam flaking methods of feed processing. Steam flaking differs from steam rolling because of the high moisture content applied and the higher contact time. This process has been seen to increase starch digestibility from 22.7-51.2 per cent. These feeds therefore, increase the performance of the reared animals.
Popping: It is a dry hot feed processing method that is applied to the seeds. This process causes sudden rapture of the endosperm. The seeds are then rolled before being fed to the animals.
Pelletisation: It is another hot processing method. It involves grinding and formulating feed and then forcing it through a thick, spinning die with the use of rollers. The feeds can be made in different diameters, length and hardness. This process alters the physic-chemical properties of the feeds due to the high pressure used. Losses are minimal during feeding and transportation because the pellets do not easily break. Pelleting increases growth rate and feed efficiency by 6.6 to 7.9 per cent respectively.
This recent technology operates on three principles: steam conditioning, high temperature cooking and high shear pressure. The process starts by formulation and tempering the mixture to about 30 per cent moisture content. Steam conditioning is the first step in this method. The aim of this step is to facilitate die lubrication and feed particle adhesion.
This increases pellet durability index and gelatinise starch. Broilers fed extruded pellets have a higher feed intake, this, therefore, increases live weight gain compared to those fed the mash.
Extrusion combines three parameters of moisture, high temperature and pressure to modify the starch and protein enhancing their digestibility.
There has been better performance in swine, fish and poultry fed on extruded pellets than those fed on the mash. The better performance can be attributed to:
The heat used in feed conditioning breaks down starch into its constituent monomers that are further broken down to monosaccharaides. On the other hand proteins are broken down into smaller polypeptides. This enhances feed digestibility due to the large surface area exposed to the enzyme hydrolysis, hence better performance of animals fed these feeds.
During pelleting, the nutrients tend to concentrate in the product and pellets are also bound together. This minimises wastage during feeding and transportation hence increasing average daily gain.
It improves energy digestibility in cereal based diets due to starch gelatinisation, unlike in the mash leading to better performance of early weaned pigs fed extruded feeds.
Helps in improved faecal digestibility of some amino acids in chicken.
Increases digestibility of proteins, amino acids and nitrogen by denaturing of the former and modifying side chains of amino acids. Starch gelatinisation together with the above changes on proteins results in better digestibility, increase feed intake, improved feed conversion ratio and performance in chicken.
Extrusion results in starch gelatinization which makes it more susceptible to amylase, this enhances starch digestibility. This improves poultry performance.
The writers are based at the Department of Dairy Food Science and Technology, Egerton University.