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Quality Control in Feed Manufacturing

“Feed manufacturers are often forced by circumstances to focus on short-term concerns such as: How many tonnes were produced this week, how many customers do I have, or how much down time did I have this week? While important, short-term problems can cause manufacturers to focus on solving problems rather than pursuing the company’s mission.”


Frank T. Jones
Center of Excellence for Poultry Science, University of Arkansas

Manufacturers who regularly examine their company’s mission tend to have a sense of who they are and where they are going. How many feed manufacturers know and regularly examine the organization’s mission? The immediate response of some manufacturers might be: “Our mission is to make a profit”. Although making a profit is certainly necessary for company survival, profit as a sole objective is short sighted.

What are we trying to accomplish when feeds are formulated and manufactured? Although there can be numerous mission statements, an overall mission of feed formulation and manufacturing might be: “To provide customers with efficiently manufactured feeds that are correctly delivered to their facilities and consistently contain the available nutrients required by animals for body maintenance, growth or reproduction”. The following “tools” are necessary for feed manufacturers to satisfy their mission:

1. Materials (feed ingredients, fuels, power, etc.);

2. Machinery (formulation equipment, feed delivery systems, feed storage equipment, feed milling equipment, etc.);

3. People

4. Procedures

Feed quality-control programs must blend these “tools” to deliver feeds that consistently contain the formulated nutrients in an available form and contain minimal levels of toxic substances. The American Feed Industry Assn. (AFIA) has defined feed quality-control programs as: “All actions directed towards ensuring the product meets the specifications established by the manufacturer”. Andrews (1991b) has described feed quality-control programs as: “A system for making sure that proper standards are maintained through use of periodic inspections.”

Any good feed quality-control program contains four components:

• Ingredient quality;

• Process control;

• Finished feed quality, and

Control of toxic substances, including pathogenic micro-organisms

Since actual quality-control policies and procedures must be adapted to the needs of each facility, this article will focus on the basics of feed quality-control programs rather than on specifics in the hope that the discussion will stimulate thinking and innovation in the field of feed-quality control.


Since many of the major feed ingredients are byproducts from other industries, feed manufacturers often find themselves in an underdog sort of position in respect to ingredients and ingredient quality. Consequently, feed manufacturers many times find themselves in the position of trying to make something good out of someone else’s dregs. Ingredients can account for 70-90% of the cost of producing feeds (Jones, 1989). Furthermore, as feed mills get larger, the percentage of the total cost accounted for by ingredients will tend to rise. Not only does it make good economic sense to pay attention to ingredient quality, but a large portion of the variation in the nutrient content of finished feeds can be traced to ingredients. In fact, one poultry company was able to associate ingredients with 40-70% of the variation in nutrient content of the finished feeds (Jones, 1989). Nutrient content variations violate the primary objective of feed manufacturing and cost in terms of performance.

What is quality? Quality has been defined by various individuals as “fitness for use” or “meeting an expectation” or “degree of excellence” or “conforming to a standard.” Although near infrared spectrophotometry (NIRS) is used by a significant number of manufacturers to rapidly determine the moisture, fat, protein and fiber content of an ingredient sample, many feed manufacturers do not analyze ingredients prior to use. Hence, most manufacturers operate on “supplier histories”. Therefore, predictability is important with respect to feed ingredients and it must be concluded that high-quality ingredients are predictable and constant in quality. Said another way, high-quality ingredients meet expectations not just some of the time, but most of the time.

It should be obvious from the preceding discussion that the first priority in the production of quality feed is to understand and define ingredient quality in specific terms. This means that ingredients must be described in two ways. First, they must be described in terms of analytical values and second, they must be described in terms of physical and/or sensory characteristics. The first depiction describes ingredients in terms that analytical chemists understand, while the second describes ingredients so that the unloading or mill personnel can make decisions about ingredient quality.

AFIA publishes a book titled “Feed Ingredient Guides II” that describes the color, odor, texture and test weight of feed ingredients. It might also be wise to provide the person receiving ingredients with a set of reference samples that include examples of both desirable ingredients and undesirable ingredients.

Ingredient-quality programs that stop with physical or sensory definitions of quality generally do not consistently obtain quality ingredients. More objective means of determining quality must be used as the ultimate judgement of ingredient quality. This objective determination is, obviously laboratory testing and analysis. While method description is not the objective of this article, it is important to be reasonably certain that laboratory results are reliable.

In the U.S. two organizations publish manuals that contain methods approved for the analysis of feeds: the Association of Official Analytical Chemists (AOAC) and the American Oil Chemist’s Society (AOCS). Analytical results from laboratories employing methods that have not been approved by the AOAC, AOCS or similar organizations can be highly questionable. Both organizations also conduct check sample programs. Check sample programs provide participating laboratories with identical feed samples for analysis. Results are then analyzed and used as a basis to provide laboratories with a letter grade (A, B, C or D) evaluation of both the accuracy and the precision of their analytical work. Check sample programs are crucial in verifying the accuracy of results. In fact, results from laboratories that are not participating in a check sample program can be challenged in disputed situation.

In a very real sense, the ingredient quality received by a given feed manufacturer may begin in the mind of your suppliers. Said another way, the ingredient quality at a given facility may well be a reflection of what your suppliers believe you want in terms of quality. Consequently, the first task in good feed quality-control programs is to design an approach to communicate your dedication to quality to ingredient suppliers.

While there can be a myriad of approaches, the following steps outline one approach to communicating your commitment to quality:

1. Commitment to quality begins with you

If you are committed to obtaining quality ingredients, your behavior must reflect commitment, otherwise your suppliers will see through your lip service and supply the ingredient quality your actions have indicated you want. This means that you must not look for bargains in feed ingredients and that quality, not price must be foremost.

2. Decide what you want in ingredients and put it in writing

Include the following in your specifications: visual appearance of the product, physical characteristics (e.g., grind or bulk density) of the product, expected analytical assay values, sampling procedures, analytical assay methods, criteria for refusing to accept ingredient loads and deficiency claim procedures. Discuss these specifications with your suppliers to determine whether or not they can supply your needs. Should your supplier indicate willingness to meet your quality needs, ask for written confirmation of acceptance. Once accepted, copies of approved specifications should be sent to the person receiving ingredients, the laboratory director and your company’s purchasing agent.

3. Examine all incoming ingredients thoroughly

It is particularly important at this point to be certain that samples of the load are collected correctly. Following sample collection, appropriate on-site quality control tests (e.g.: moisture, test weights, mycotoxins, rancidity, etc.) should be performed. If the load is found deficient, it is important to reject the load. While rejection of deficient loads may seem to be a drastic step, it is a step that will leave no doubt in your supplier’s mind as to your commitment to quality.

4. Have ingredient samples analyzed by a qualified laboratory

The values obtained from these analyses will provide you with a continuing evaluation of the quality of your supplier’s product. This step is also necessary since laboratory results are necessary to provide the ultimate judgement of ingredient quality.

5. Communicate often with your suppliers about quality

Let your suppliers know that you are aware of the quality of their product. This will help your suppliers know that you really care about receiving high-quality ingredients.

6. Adjust your formulas to reflect the assays you are receiving

If you do not adjust your formulas to reflect the actual assays, you have, in effect, wasted much of the time and money you spent on the assays.

7. File every deficiency claim possible

Filing these claims will put added “teeth” to your ingredient quality program. Dr. W. Edwards Deming is perhaps the most renowned authority in the world on the subject of quality and productivity. Dr. Deming’s 14 Points of Management were reviewed and illustrated by Benoff (1991). While most of Dr. Deming’s 14 Points of Management apply to company structure and personnel management, the following point (point 4) applies to feed quality control programs:

“End the practice of awarding business on price alone. Instead, minimize total cost by working with a single supplier”.

Benoff (1991) points out that, traditionally, purchase contracts have been awarded to the lowest bidder who meets the specifications. This system is supposed to force competition between suppliers, driving the price down and quality up.

However, purchasing on price alone does not account for all of the cost connected with the use of products, since there is a cost of use associated with each product. In other words, the production system must be adapted to the use of each product. While adaptations cost, this cost is often ignored because it is difficult to measure. In terms of feed-ingredient quality, this means that variations in the nutrient content of finished feeds may be associated with the number of suppliers and that each supplier is an additional source of variation. These variations lower quality and raise costs. Thus, obtaining ingredients from a single supplier who cares about quality may make economic sense.

The process by which high-quality ingredients are made into high-quality feeds involves three components within the feed mill: personnel, machinery and procedures. If quality is lacking in any of these three components, the consistent production of high-quality feeds is unlikely. However, it is equally important to ensure that personnel, machinery and procedures are “blended” together toward the goal of efficient production of high-quality feeds.

Personnel: Three general characteristics should be sought in new mill employees productivity, interest or alertness and the ability to work as a team member. Once hired, employees should be quickly and efficiently trained to do their jobs. This training should include not only what job to do, but why the job is necessary. Employees should be informed initially and reminded periodically how important their job is to the total effort.

Once trained, the company saves money if employees are encouraged to stay with the company. This means employees must be motivated either by the work or by the manager to remain on the job. Employee motivation is a difficult and complex affair. In fact, it is said that Dr. Albert Einstein once remarked to a psychologist that understanding the theory of relativity was child’s play in comparison to understanding people. Nonetheless, employee motivation is a reality faced by virtually every person involved with feed mill management.

While a multitude of suggestions could be made at this point, only one seems appropriate. Company commitment to quality must be supported by everyone from top management down. Employees who do not follow the company policy on quality will tend to undermine the program. For example, put yourself in the feed mill employee’s place in this situation. As the ingredient unloader, you are instructed to examine each load to determine if it meets company specifications. If this employee is given a hard time when he/she discovers what is believed to be a deficient load, what does this say to him/her about the company’s commitment to quality? The feed mill employee who discovered a deficient ingredient should be recognized for a job well done.

Machinery: Equipment selection, operation, repair and troubleshooting can become a very complicated matter, which cannot be covered adequately in a short space. However, applying the following general points to each specific piece of equipment will help reduce machinery problems:

1. Application: Was the equipment designed to do the job it is doing?

2. Installation: Was the equipment installed according to the manufacturer’s recommendations?

3. Adjustment: Are the critical adjustment points within the machine set correctly?

4. Operation: Is the machine being operated according to the manufacturer’s recommendations?

5. Capacity: Is the equipment being run within the rated capacity?

6. Lubrication: Is the correct amount of the proper lubricant used within the correct time frame in the machine?

7. Maintenance: Can you predict when maintenance and possible repairs will be needed on each piece of equipment? Do you have parts and tools to do maintenance and repairs?

Procedures: Procedural difficulties are usually fairly easy to identify since problems will tend to repeat. However, every procedure instituted should incorporate the following:

1. Communication: Does the person doing the procedure understand what is expected? If another person had to take over this job would he/she understand?

2. Identification: Are controls on equipment clearly identified? Are bagged ingredients clearly labeled and stored in an orderly manner?

3. Traceability: Will this procedure allow you to trace problems to their source?

4. Verification: Are samples being taken and stored that will allow you to verify the source of the problem?

5. Records: Are all records being kept of use? If records are of no use or potential use discontinue collection. Useful records should be stored in a clean, safe and accessible place.


Once quality personnel, machines and procedures have been established, control can best be maintained by applying effort at the “quality pressure points” in the mill. These “pressure points” are:

1. Ingredient inventories: Ingredient inventories can be frustrating to mill personnel. However, since inventory programs provide manufacturers with a means of checking to see that the correct amount of ingredient has been used in a given time period, these programs can allow manufacturers to catch mistakes before they get out of hand. Mc Ellhiney (1981) pointed out that good ingredient inventory systems meet the following criteria:

• They are simple and understood by all,

• They include physical inventories,

• They are accurate,

• They consider history and forecasts, and

• They are used.

Whether the system is simple or complex, all inventories, except those for drugs, should be done at least weekly by the same person. Drug inventories must, by law, be perpetual. Projected and actual use of ingredients should be reconciled. In this reconciliation, Andrews (1991b) pointed out that the following tolerances are acceptable: less than 100 lb., 4% variation; between 100 and 4,000lb., 2% and more than 4,000 lb., 10%.

2. Bin cleaning: If bins are not periodically cleaned, ingredients or feeds can build up on the sides, encouraging mold growth and cross contamination. Thus, finished feed and ingredients storage bins should be inspected at least once each month and cleaned as needed. While such cleaning is vital, employee safety is even more vital. Consequently, prior to entering any bin for cleaning the following precautions should be taken:

• Verify that the bin is suitable for entry (e.g., is it too hot? Are there detectable chemical fumes?),

• Verify that the lock out program has been activated and notify other operators that you are entering the bin,

• Be certain that a responsible, trained individual will remain with the person for the duration of his/her stay in the bin,

• Verify that lighting, hoisting, safety and respiration equipment functions properly, and

• Verify that first aid equipment is well supplied and ready for use.

During cleaning, a minimum amount of water should be applied to bins, since excess moisture can require time to evaporate, possibly encouraging mold growth and corrosion of metal bins.

3. Verification of equipment cleanliness and condition: While maintenance procedures should ensure that equipment is periodically examined, certain critical points and equipment pieces should be examined more frequently. Discharge gates and elevator boots should be cleaned and inspected for wear or leakage once each week. Elevator head pulleys should be checked for correct alignment, heat and wear once each shift. Turnheads should be examined for correct position and wear on a weekly basis. Scalpers or ingredient cleaning equipment should be checked once each week.

4. Grinding: If the hammermill and/or other grinding equipment does not operate correctly, then mixing, pelleting and animal performance may suffer. Thus, hammer condition and wear should be checked daily. Magnets should be cleaned and checked for correct operation daily or at the shift change. Grind consistency should be checked once each shift using a U.S. # 8 sieve. For pelleted feeds, all ground grains should pass through the sieve. Larger particle sizes are generally required for mash feeds, since the fine particle sizes required for pelleting are costly and can cause flowablility problems in feed storage tanks. Special attention should also be paid to the removal of heat from ground grains exiting the hammermill. If ground grains are not cooled, the heat can cause moisture migration leading to excessive mold growth. In addition, excessive moisuture or heat can cause ground-grain tanks to deteriorate more rapidly than normal. Air-assisted grinding can reduce the heat associated with grinding.

5. Batch system validation: While there is considerable opposition to the Food & Drug Administration’s proposal to legally require batching and mixer validation, batch system validation can provide feed manufacturers with information that may not be attainable in any other way. Batch system validation should be done on a semi-annual basis. Begin the validation process by verifying that a clean finished-feed bin is available. Next, batch and mix a mash formula in the usual manner and record the batch weight. Convey the batch to the clean finished-feed bin, load it out into one compartment of a bulk truck and record the truck weight. Repeat this process until four compartments have been loaded. Batch weights and truck weights should be within 1% of each other. If weight differences are more than 1%, begin by checking the following in the batching system:

• Batch and micro-scale accuracy;

• Conveyor integrity (Is there a leak?);

• Bin integrity (Is there a hole in the bin wall);

• Turnhead position and maintenance (Does some feed get diverted to another bin?), and

• Mixer and batch scale slide gate operation (Does one batch leak into another?).

6. Mixing: Mixing is probably the most critical step within any feed manufacturing situation. Yet, in a recent survey, Wicker and Poole (1991) found that more than half of the 145 mixers tested were not providing an adequate mix. The authors attributed mixing inefficiency to:

• Insufficient mix time,

• Operation of mixers beyond designed capacity, and

• Worn altered or broken mixing equipment.

While equipment manufacturers have made great strides in providing their customers with durable mixers that rapidly and efficiently mix feeds, it is obvious from these data that many times mixers and the mixing operation is taken for granted or ignored. Batch mixers should be examined weekly to be certain that shafts, ribbon paddles or screws are in good repair and contain no buildup. Mixing times should be checked at least twice each year.

Sometimes premix manufacturers will check mixer times as a service to their customers. However, no matter who checks, mixing time should be correctly evaluated. Procedures for checking mixing time are outlined by Jones (1999) and in Feed Manufacturing Technology IV, which can be purchased through AFIA. While coefficients of variation (CVs) of 10% or less are generally thought to indicate a homogenous mix, Wicker and Poole (1991) pointed out that CVs of 4-7% are attainable in production situations if equipment is operated correctly.

7. Pelleting and Pellet Cooling: Pelleting and pellet cooling is probably the most complex process within the feed mill. While pellet process controllers have made control simpler and more accurate, the following indicators of quality should be examined on a regular basis:

• Conditioning temperature: Conditioning is probably the most important part of the pelleting process (Andrews, 1991a). When feeds are adequately steam conditioned, pellet durability is optimized due to starch gelatinization and moisture loss in pellet cooling is maximized because the moisture holding capacity of the air around pellets in the cooler increases with heat. In addition, the heat of conditioning is important in the activation of mold inhibitors (Tabib et al., 1984) and the destruction of pathogens such as salmonella (Blankenship et al., 1984). Conditioning temperature should be as hot as possible (preferably greater than 180° F). However attention should also be paid to feed vitamin levels of pelleted feeds, since 10-25% of the fat-soluble vitamin activity can be destroyed by the pelleting process (Jones, 1986)

• Cool-Pellet temperature: The temperature of adequately cooled pellets (or crumbles) will be within 10;dF of atmospheric temperature. When pellets are inadequately cooled, moisture migration, mold growth and bin corrosion problems are likely to occur. Cool-pellet temperatures should be checked once each shift.

• Moisture gain: Moisture gain from pelleting is checked by comparing the moisture of the mash prior to pelleting with the moisture of the cooled pellets. Moisture gain can accelerate mold spoilage problems. While no moisture gain is a worthy goal, a more attainable goal is less than 0.5%. Moisture gain should be checked once each month.

• Crumble texture: The texture of crumble feeds should be closely controlled, since incorrect crumble size can lead to palatability problems and inefficient animal production. Yet there are difficulties sometimes in determining the correct crumble size. While rules of thumb are dangerous, field experience suggests that about 50% of correctly sized crumbled feeds will be retained on a U.S. # 12 Sieve.

• Pellet durability: Many of the benefits of pelleting on growth and feed conversion are due to the physical form of the feed. Thus, durable pellets could have a positive effect on animal performance. Correct procedures for the determination of pellet durability are described in Feed Manufacturing Technology III, which can be purchased through AFIA. However, it is important to understand that the pellet durability procedure has a certain amount of inherent variation that must be taken into account when interpreting results. Consequently, at least five samples of a given feed should be tested in order to determine the average durability. Durability should be checked at least once each week, preferably daily.

8. Meters and Scales: If the mixing process is under control, whether or not the formula is made according to the nutritionist’s recommendation may well depend on the accuracy and adjustment of the scales and meters. Thus, each facility should own and use test weight to check the calibration of scales weekly. Batch scales should be cleaned and inspected at least once each month, while micro-ingredient scales should be cleaned and checked weekly. All scales should be professionally serviced at least twice each year. Liquid metering devices should be checked and adjusted as formula runs are changed. Metering devices should also be checked periodically during long formula runs.

9. Truck inspection and cleaning: Trucks are sometimes overlooked as a source of moisture, mold and drug contamination. Truck drivers should be held responsible for the soundness and cleanliness of their trucks (both inside and outside). However, it is important that mill workers ensure that trucks are clean and in good repair prior to loading.

In many situations, feeds are used rapidly following manufacture and animals consume the feeds before any assays can be performed. However, finished-feed assays are necessary and important because they provide the mill with a “final report card” on how well quality was controlled.

How much finished-feed sampling and analysis should be done? While the answer to that question will depend on numerous factors, a general rule of thumb is to collect one sample of each formula per week or one sample per 100 tons of production, whichever is greater. When a problem is discovered, it should be addressed and resolved as soon as possible. The steps outlined below are one method of addressing finished-feed problems:

1. Is the assay correct? Ask the lab to recheck the assay and continue to examine the problem.

2. How was the sample taken? Was the sample representative? You may want to resample it if the material is still available.

3. Is only one nutrient level out of control or are several? This could be clue as to whether a certain ingredient was left out of the formula.

4. Was the regular crew operating the mill when the feed was produced?

5. Check inventory records for any discrepancies between the actual and predicted inventory records.

6. Check the scales and metering devices for correct adjustment.

7. Check ingredient and finished-feed bins at the feed mill for hang-ups or bridging problems.

8. Recheck the mixing time to be certain it is correct for the ration involved.

9. Check the ingredient assay values to see if they indicate a deficient load was received. If a deficient load was received, contact you ingredient supplier immediately.

10. Check the formula matrix to be certain that ingredient assay values are correct and reflect the values presently being received.

After going through these 10 steps, it is possible that you may still not know what caused the problem. While this is frustrating, your efforts have not been in vain. Laboratory personnel, the mill crew, the office staff, the nutritionist and several other persons have all become aware of your company’s dedication to the production of high-quality feeds. If problems are consistently addressed as they occur, the mental image of dedication to quality will become fixed in the minds of the people involved and this image can only work for your good.

We also suggest you to read our previous article titled "Quality Control in Feed Production".

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