Compound feed prepration
The compounding of animal feed involves processing and blending of raw feed ingredients of wide ranging physical, chemical and nutritional composition into a homogenous mixture suitable to produce desired nutritional response in animal production. Certain feed ingredients such as cereals, oil seed cakes and their extractions, meat meal, blood meal and fish meal undergo processing prior to their inclusion into a compounded feed.
After procurement, quality of raw material is checked as per approved procedures and then stored in the water proof, well-ventilated stores, equipped with wooden pallets and placed away from the walls. The ingredients could also be stored in concrete or steel silos or in bins with a sole objective to protect the raw material from insects, pests, birds and rodents. The proper storage of raw materials is not only essential to prevent physical losses, but also to check deterioration in quality.
The feed compounding process consists of following sequential procedures:
(a) Grinding of ingredients
(b) Mixing of ground ingredients
(c) Pelleting of mixed feed
Allied machinery for feed processing
Processing of feedstuffs and raw materials requires machinery at different stages of handling and processing in to the finished products. Usually, raw materials arrive in to the feed mills in trucks, which are stored in the godowns after weighment, processed (grinding, mixing, pelleting and packing) and dispatched to the markets. Following machinery is required at different stages:
• Weigh bridge
• Hammer mill , Attrition mill, Roller Mill
• Pellet mill
• Bins for storage of raw materials
• Molasses tank
• Hydraulic press in case of complete feed block manufacturing
• Pulverizer in case of mineral mixture manufacturing
Weighing bridge: Weigh bridge of suitable capacity must be located at the entrance of feed mill. Besides this, arrangements for other accurate balances of smaller capacity should also be made available for weighment of bags of finished products and feed supplements (urea, mineral mixture etc) added to each batch of the feed during the course of processing.
Augers: Augers are steel tubes containing a continuous screw which convey meals along its length as it is driven by a motor. Augers are available in various designs and diameters. Augers designed to convey high bulk density material may also be suitable to convey to low bulk density material. Augers may be used in a horizontal or inclined position, but not suitable for vertical movement of materials.
Bucket elevators: The bucket elevator consists of a tall metal or wooden box in which runs an endless chain fitted with buckets movers. Buckets are filled at the base of the elevator and discharged at the top. These are suitable for lifting raw materials vertically to grinder mixer or pelleter and for lifting pellets to a cooler.
Conveyors: Conveyors are used for the horizontal movement of large quantities of feed materials. Action is just like bucket elevator but in case of conveyors the buckets are replaced with slats, chains or baffles to drag material from one operation to the other.
Hammer mill: Hammer mill is used for reduction in particle size of raw materials.Particle size reduction can be achieved by cutting, crushing, shearing or impact grinding. Hammer mill is based on the principle of impact grinding, however in some hammer mills, having the arrangement for grinding, and in the case of dried roughages such as hays, provisions are made for cutting the long sized roughages before exposing the material for impact grinding. Normally hammer mill is used for particle size reduction of cereals and oil cakes etc. Inside the grinding chamber, hammers are fixed rigidly to the central shaft or more often swinging on steel pins rotate at high speed. The impact of the raw material on the hammers and the continual high velocity impact of particle results in material breakdown until it is small enough in size to pass through a perforated screen. The smaller screen size requires more work to reduce the particles to the desired size and the grinder motor requirement will also be of high ‘Horse Power’. The ingredients having high bulk density get grooved more easily than fibrous low density materials. Grinders run efficiently at maximum capacity for a particular raw material and screen size. The grinding operation may generate considerable quantities of heat and dust, and temperature of raw material increases by 10-20°C. The pieces of string, metal, wood, glass or stones, which could cause extensive damage to machinery, should be removed from the raw material before it takes entry into the grinder. For the cooling of ground material, usually air is drawn into the grinding chamber and also during the pneumatic conveying of material from the grinding screen to its point of discharge.The small grinders have suction fans fitted to the grinder shaft which bring about cooling and conveying of ground material in one operation. Other grinders discharge material directly into conveyers and the air drawn during grinding is released through filter bags. Grinders may operate in a horizontal or vertical direction according to design.Raw materials for poultry feed and those used for pelleting should be fine ground
than for feeding cattle or pigs. The materials to be ground in a hammer should not normally contain moisture beyond 13-14%, otherwise it may clog the hammer mill. Large, lumpy, and hard materials such as expeller oil cakes, dried cassava roots, etc. should be pre-crushed in a cake breaker to a particle size suitable for pushing into the hammer mill.
For particle size reduction, especially for cereals other alternatives such as attrition mill or roller mill may be employed. Roller mill consists two rolls, usually corrugated, rotating in opposite direction at similar or variable speed. The material is fed between the rollers and if both the rollers are moving with the same speed, particle size reduction takes place as a result of crushing and in case of variable speed, cutting and shearing both take place.
Cyclone: During pneumatic conveying, the air and material are separated in a cyclone. Cyclones are 95% efficient in separating ground particles and air, and a cloth or other type of filter is necessary as a dust barrier.
Mixers: The ground ingredients are homogenously blended in a mixer. Mixing improves feed palatability and ensures wholesome consumption. Mixing equipments of different types with tumbling, stirring, smearing and impact actions have shown that the rate of mixing depends upon the physical attributes of the materials to be mixed as well as the type of equipments used. However, materials having similar physical attributes such as shape and size of particles and bulk density, difference in the equipment do not make much difference. To test the mixing efficiency of different mixers, measurement of some internal markers such as common salt or silica is done in the representative samples collected from different locations of the mixers as these measurements are comparatively easy, economical and less time consuming. Following methods of mixing are in practice.
Mixing with shovels: Small quantities of animal feed can be adequately mixed manually using shovels. The ground raw materials should be layered one above the other, mixed and turned to form one heap. Mixing of the heap for 3 to 4 times may produce an acceptable product which ensures even mixing of small quantities of vitamins, minerals and other supplements.
Concrete mixer: Concrete mixers, driven either with electric motor or oil engine,
are mobile and low cost machines suitable for mixing dry or wet feed ingredients. Pre-ground raw materials could also be mixed for 4-5 minutes prior to grinding to obtain a better blend. It is a type of batch mixer used to mix small quantity of materials.
Vertical mixer: It is having a vertically running screw of about 8-10" diameter, in which raw materials are continuously tumbled, intermingled and discharged through a fountain type action. The raw material takes entry either at the top from a cyclone or auger connected to the grinder or at the base of the screw. It is a slow and long dwell
time mixer, normally takes 10-15 minutes. Its discharge is collected into a bag or conveyed by auger or bucket elevator leading to a storage bin or pelleter.
Certain liquids like molasses, oils and fats, phosphoric acid, choline chloride etc
are added in the formulation as source of nutrients, to check dustiness, to preserve the shelf life or palatability of feed. Vertical mixers are less effective in uniform mixing of liquids, may be due to its design and slow running, also encourage particle size segregation. It is also a low cost machine, widely used where liquid addition is not required. or mixing micronutrients such as minerals, feed additives or drugs, usually premix is added to each batch. Premix is a uniform mixture of micronutrients with diluents or carriers to facilitate their mixing in whole feed. For manufacturing the premix, a separate small mixture is usually used to avid the contamination.
Horizontal mixer: The horizontal mixer is having a U shaped trough with a
horizontal turning mixing shaft to which the paddles or agitators are attached and these run very close to the walls of the trough. The ground raw materials are lifted, folded and abraded against each other resulting in a relatively short mixing time (3-6 minutes) depending upon the nature of the mix. Two or three mixes can be obtained in the same time as one mix in vertical mixer. The mixer is suitable to blend up to 8% liquid in the dry feed. The molasses and fats are heated before adding to the mixer. The horizontal mixer is costlier than the vertical mixer.
Conveyor mixer: Conveyor mixer consists of a trapezoid metal box in which mixing is affected by slats extending almost the full width of the machine. Slats are carried on a pair of endless chains. This machine is also having limitation to end liquids into the mixture.
Besides cost component of equipments, energy is the major recurring expenditure
for the processing of feedstuffs in a feed processing unit. Energy requirements are of manual (skilled and unskilled) or in the form of electrical power and fuel. The electrical power consumption in a feed unit and proportional motor size and cost for feed milling has to be estimated in view of the capacity of feed plant.
Pelleting: Pelleting involves the compression of a mixed feed through holes in a hardened ring or plate called die by means of hardened steel rollers. Feed pellets are of two types viz. cold pellets and hot pellets. In the cold pelleters, the mixed feed is directly pushed from a bin or auger in to die head at ambient temperature and the material is not given any heat treatment, however, the frictional force, generated during pellet extrusion, may increase the temperature of pelleted feed up to 60- 70°C. The pellets must be cooled before packing or bagging and the moisture content should also be brought down to 12%. Such pelleting machines usually have low capacity (1 tonne / h) but it all depends upon feed ingredients, particle size, moisture content and diameter of the pellets. In conditioner pelleting, the mixed meal is directly pre-heated with dry steam (steam in vapour form) in a small high speed mixer called conditioner. The steam conditions the meal to the preferred temperature and moisture. During pelleting, temperature of the meal rises by about 100C with an increase in moisture. Therefore, dry and cool air is employed through a cooler (vertical/ horizontal) through a moving mass of pellets. The output of the pellet mill increases 100% with improved texture, if meal is pre-conditioned prior to the pelleting. Therefore, additional arrangements for steam supply have to be maintained, which involve additional expenditure.Components of a traditional pellet unit are supply bin, pellet mill, Cooler, crumbler, elevating system , Sifting device and steam supply. In a ring die pelleter, rollers or the die may be driven but in a plate die pelleter the rollers only are driven. The die and rollers of a ring die pelleter may operate in a horizontal or vertical plane according to machine design. The pelleting process is very energy intensive, demanding up to 50% of the total power required for feed manufacturing. The diameter of feed pellets depends upon the diameter of the holes in the die ring. Smaller the die holes, greater force is required to push the meal into the holes, hence greater the power demand and increase in the cost of manufacturing. Demand of power further increase in case pelleting is done without steam supply. Use of crumbler is necessary when pellets are crumbled for poultry feeding.
The pelleting reduces dustiness as well as feed losses, releases oils which lubricate the pellets, increases palatability of inferior feed ingredients, inactivates anti-nutritional factors as well as some pathogenic bacteria and increases rumen escape proteins. However, pelleting raises the cost of machinery and involve high energy consumption requirement. Molasses is generally added to the mixed feed prior to the pelleting, which acts as a binding agent and also as a sweetener. Quality of pellets largely depends on the amount and nature of starch and proteins in the mixed feed and binding effect depends upon moisture, fiber, oil contents and particle size of the mixture to be pelleted. Although the pelleting process involves sizable additional cost, animals prefer pelleted feed over mash feed. Besides this, pelleting improves the nutrient utilization and reduces the chances of adulteration. Therefore, pelleting is practiced especially for ruminant feeds.
It is suggested to incorporate variety of particle sizes in the formula to improve the pellet quality and production rate as small particles can fill the void between the large particles during the course of pelleting and eliminate the air space and void between particles. However, size of particles must be kept in balance with the diameter of pellet that is being produced. Same particle size of ingredients results in lower pellet quality and production rate.
Pelleting can affect the natural vitamin content of feed ingredients as well as the vitamins added in the form of commercial products. Modern forms of vitamins are usually less affected by the process, because they are especially developed for use in animal feeds. The protection of sensitive vitamins chemically is done with an antioxidant and physically with a protective coating. The coating is frequently a gelatine-based matrix, though the specific product design differs according to the supplier of the vitamin products. Vitamin products, currently marketed for feed application, show generally good stability in pelleted feed.
To achieve the good texture and better utilization of pelleted feed, following points must be considered:
• Avoid caramelization of feed ingredients such as dried milk, whey or sugar incorporated in to the mash by maintaining the temperature less than 60 0C by reducing the steam supply. Using a thin die to reduce the frictional heat or addition of fat to improve the lubrication may also be used to avoid the plugging of die as a result of caramelization.
• In case of pelleting of urea supplemented feeds, little or no heat should be applied as urea becomes more soluble on increasing the temperature and moisture added by the steam further facilitates this solubilization.
• To avoid the addition of moisture in case of pelleting of molasses supplemented feeds, steam supply must be restricted as molasses consists about 26% moisture. Addition of steam at the point of conditioning would increase the moisture content of pellets, which may cause plugging of die.
• Since heat is more important than moisture to reduce the protein degradability
and its better utilization, feeds having highly degradable vegetable protein should be given more heat exposure.
• Feeds having high starch content should be exposed to high temperature and
high moisture to facilitate its gelatinization during the course of pelletization, as it helps in better utilization of dietary starch.
• Pelleted diets having high fiber and low grain content should be pelleted at <
600C and maximum moisture level at 12 to 13% otherwise pellets may develop cracks and deteriorate their texture.
The moisture and heat that can be added will be influenced by the type of pellet
mill, dies, rollers, and environmental conditions that exist. Therefore, these should be standardized to create the optimum conditions for better utilization of available feed resources.