Premixing feed ingredients
July 01, 1996
by Teresa Acklin
Premixing certain compounds is important to manufacturing a quality feed.
A properly mixed feed should contain consistent levels of each ingredient throughout the batch. Premixing is an important part of a quality feed manufacturing process because it allows small-inclusion nutrients or compounds to be more uniformly or safely distributed throughout the feed.
Consider the example of a 1-tonne batch that contains 1 gram of a microingredient that is critical to the final mix and animal performance. If you try to add the microingredient directly to the batch, it can become airborne, it can become electrostatically charged and cling to the mixer, or it can migrate to dead spots. And the limited quantity can reduce dispersion.
Premixing is used to ensure proper distribution of these nutrients in the final feed. Vitamins, trace minerals, antibiotics, mold inhibitors and flavors are predominately added to feeds in the form of premixes. The accompanying figure helps define premixes in relationship to other feed components.
Premixing can reduce animal and human exposure to potentially harmful compounds by diluting them to approved and safe concentrations. Premixing also can standardize potency, especially with certain fermented antibiotics and vitamins that have variable potency coming out of the fermenters.
The premix process requires careful attention to several points to ensure success. These include formulation, selection of carriers or diluents, use of dust control and binding agents, mixer type, sequence of ingredient addition and mixes, mixer clean-out, packaging and storage.
This initial step is extremely critical. Whether one is given a set of specifications or is responsible to generate a set, formulation is a necessary first step. Many premixes are incorrect because of improper interpretation on the part of the formulator.
Proper conversions involving units of measure are important. The formulator also has to consider the ingredient source, bulk density and particle size variations, cost comparisons, handling characteristics and possible interactions before final decisions are made.
Nutrient availability and potency of vitamins and minerals will vary between sources and these factors need to be considered in formulating high quality premixes. Some low cost vitamin sources are available at below market prices, but are of questionable quality and stability. A thorough knowledge as to source and potency of the vitamin sources is advisable.
Formulators must consider stability and possible interactions when putting together their specifications. Much discussion about the combination of vitamins and trace minerals in the same premix continues among nutritionists.
If wise decisions are made on types of carriers, packaging and storage times and conditions, as well as using quality vitamin suppliers, combinations of vitamins and trace minerals are no problem. Convenience, cost savings, and mixing efficiency can be advantages to premixes containing both vitamins and trace minerals.
Carriers or Diluents
The purpose of a carrier is to physically accommodate fine-powdered microingredients and provide a uniform distribution in the process. Rice hulls are a commonly used carrier in vitamin premixes because of their uniformity, pore shape and degree of porosity, which permits fine particle stabilization. Other common carriers include calcium carbonate, maize cob fractions and wheat middlings.
Diluents, on the other hand, are used to extend or dilute the microingredients. They effectively act as a flow agent, affect the density of the mix and provide volume to the premix. One of the most common diluents used in a premix is calcium carbonate.
Combinations of various carriers are often used, for cost considerations, to obtain desired bulk density and to maximize stability. The different carriers, diluents and their combinations are varied in their use depending on the purpose of the premix and its use in the mixed feed.
Low priced premixes often use a high proportion of calcium carbonate and call for a high use level in the mixed feed. Nutritionally, this could have a negative effect on the calcium to phosphorus ratio and thus, performance, even though it was a lower priced premix.
Cost should not be the driving force in making a decision on which carrier or diluent to use. Rather, emphasis of these components in a premix should be related to their ability to carry micro-ingredients and their compatibility with other ingredients and mixes.
Dust Control/Binding Agents
Fats and oils serve a very important function in quality premixes. They act as an adhesive on the surface of a carrier to improve holding capacity of that carrier for microingredients. Binding agents also reduce dustiness, improve the integrity and uniformity of the premix and reduce electrostatic charges and random loss of microingredients.
Mineral oil, vegetable oils, and fats can all be used in selected premixes. Intended purpose of the premix, type of carrier, amount of carrier and cost of oil or fat all influence one's choice. Mineral oil is the most widely used dust control agent for concentrated premixes, while other oils and fats are used in the more diluted products.
Many times the type and amount of dust control/binding agent used is compromised because of cost competitiveness, which can result in poorer quality premixes. Some fats, if not stabilized, can cause destruction of vitamins.
Application of oils to mixes under pressure to create an atomized oil droplet is the preferred method. This will ensure uniform application and a better quality mix.
Horizontal or rotary drum mixers are necessary for proper premixing because they handle a wide range of bulk densities, produce less friction and, therefore, less heat in mineral mixes, and provide for a greater surface area exposure when adding liquids.
Ease of loading, suitability for applying liquids, mixing efficiency, ease of discharge, and clean-out requirements must all be considered. Short cuts in these areas can result in major problems. Manufacturing premixes is not the same as manufacturing complete feeds. The same equipment is not always suitable for both, especially to ensure mix uniformity and minimize any carryover.
In loading a mixer, proper sequencing of the various ingredients can affect the quality of the final product. Oil balls, chemical interactions and particle segregation can all result if proper mixer loading sequencing is not followed. These considerations are even more important with premixes.
Poor quality premixes are costly to the premixer and also the feed manufacturer and ultimately the producer. During the premixing process, the following procedure should be used:
charge the mixer with the carrier, then thoroughly disperse the oil (binder) onto the carrier. This preconditioning step will maximize the carrying capacity of the carrier. The diluent can be added any time in the process. The microingredients will be added after the preconditioning phase to minimize oil balls and dustiness. Depending on the specific makeup and characteristics of the premix, the addition sequence may have to be modified.
Mixers do not completely empty and, therefore, present a potential carryover from one mix to the next. Mixers vary in clean-out efficiency and steps must be taken to minimize the carryover from one mix to the next. Physical clean-out using air or brushes may be needed between mixes. In specific situations, it may be necessary to flush the entire system with rice hulls between mixes to decrease contamination.
Proper sequencing of mixes is a practical way to minimize the potential negative effects of such a carryover. Drugs that require a withdrawal and compounds that are toxic to some species are prime examples where sequencing is essential.
All drug mixes should have a sequencing schedule. Premix manufacturers especially must follow strict sequencing even after proper clean-out because high potency and potentially dangerous ingredients or compounds are involved.
Packaging and Storage
Packaging material should be selected based on the type of premix involved. Moisture can be very detrimental to the stability of certain vitamins or other compounds; therefore, a vapor barrier in the packaging material is important. Some ingredients used in premixes are hygroscopic and require a vapor barrier.
Length of storage and type of handling may also require special packaging consideration. For example, premixes intended for exporting may require stronger packaging materials because of handling concerns and weather variations.
Labeling is extremely important for regulatory purposes and also to ensure proper use. Be sure all products are accompanied by a label. Date coding requirements are not uniform, although they should be. Clear and easily determined date coding is useful in product rotation, biopotency concerns and establishing expiration dates.
For premix storage, dry, cool conditions are most desirable, and an effective insect and rodent control program must be a concern in storage areas. High potency premixes can be expensive products; therefore, proper storage to ensure quality and your company's investment is extremely critical.
Several studies with properly formulated and blended vitamin and trace mineral premixes have shown good stability up to 90 days in storage using accepted analytic assays. However, few situations offer advantages to storing premixes for more than 30 days.
This article is based on a paper by Dr. Dwight Armstrong, president of Carl S. Akey, Inc., Louisburg, Ohio, U.S., and a director with the American Society of Animal Science; and Dr. Keith Behnke, extension specialist, feed manufacturing, Kansas State University, Manhattan, Kansas, U.S.