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Ensuring Optimum Mixability In Feed Manufacturing

Introduction
The daily ration of nutrients that an animal receives from a feed may vary from time to time due to a number of reasons. The sources of variation will probably cause variation in the day-to-day level of nutrition received by an individual animal. Certain nutrients are guaranteed to be present at minimum levels and regulatory officials will be concerned, if guarantees are not met. Certain ingredients may be toxic at very high levels.

The nutrient variation in feeds is most likely to occur for the following reasons (Wilcox and Balding, 1976):

a.Variation in the composition or quality of ingredients from batch to batch or from time to time
b.Poor mixing or segregation after mixing
c.Errors during weighing or proportioning

In most cases, a sound quality control program can insure optimum feed preparation. Routine inspection of the mixer, proper mixer ¡ã¡Þtuning¡ã¡À, maintenance of all liquid systems and close attenti to ingredient inventories will go a long way to ensure that the nutrient specifications prescribed by the nutritionist, actually reach the bird.

The consequences of nutrient level variation are varied. However, the major disadvantage of variation is normally the effect on animal performance.

Mixing is one of the most essential and critical operations in the process of feed manufacturing, yet it is frequently given little consideration. The objective in mixing is to create a completely homogeneous blend. In other words, every sample taken should be identical in nutrient content. A functional definition of uniform mixing can be summarized in one sentence. ¡ã¡ÞAll nutrients will be present in sufficien quantity in the daily feed intake of the target animal to meet its minimum growth requirements¡ãO¡ã

The literature is filled with classic examples of the impact of inadequate vitamin and mineral consumption on animal performance. However, field examples are rarely ¡ã¡Þclassic¡ã¡À in nature, and are therefore, ve difficult to diagnose. Unfortunately, in most cases the effect of inadequately/ improperly mixed feed manifests itself as marginally depressed performance. Typically, birds exhibit slight reductions in growth, feed conversion, feathering and other performance parameters. As a result, the technical staff of a commercial company may incorrectly diagnose a decease condition, and never resolve the underlying problem in the mill.

Effect Of Mixing Uniformity On Animals Performance
Uneven ingredient dispersion feeds may lead to reduced bird performance. In order for birds to reach their genetic potential for growth and meat yield, levels of protein, energy vitamins and minerals must be provided in their proper ratio. Duncan (1989) reported that as protein variation increased in feeds, growth rate and feed conversion were depressed (Table 1). A 10% variation in the feed quality significantly reduced both weight gain and increased feed conversion. When the coefficient of variation (CV) of the feed was increased to 20%, another significant increase was observed in feed/gain (F/G).

A recent study on the effect of mixing uniformity on day one old broilers was conducted by McCoy et al. (1994). Feed was formulated to meet or exceed NRC requirements for all nutrients for broiler chicks from 0 to 3 week of age. However, in experiment 2, feeds were formulated to 80% of NRC recommendations for crude protein (CP), lysine, methionine, Ca, and P. The purpose of using deficient diet in this study was to accentuate any difference in growth performance that might result from diet nonuniformity.

In experiment 1, feeds were collected from mixer after 20, 40 and 80 revolutions of mixing (20 = highly non-uniformity mixing, 40 = moderate non- uniformity mixing and 80 = uniform mixing). Variability of feed decreased sharply between 20 and 40 revolutions and no further reduction occured between 40 and 80 revolutions (Table 2). The CV values from analyses of salt concentrations were 43, 11 and 13% for 20, 40 and 80 revolutions, respectively. No difference occured among treatment for average daily gain (ADG), average daily feed intake (ADFI), bone strength, bone ash, carcass crude protein, carcass fat, or carcass ash. However, there was a trend for a linear increase in gain:feed (G/F) ratio when mixer revolutions were increased.

In experiment 2, feeds were collected after 5, 20, and 80 revolutions. The salt test CV % decreased from 40.5% to 12.1% when mixing was increased from 5 to 20 revolutions, but there was no further reduction of CV % from 20 to 80 revolutions (Table 3). ADG, ADFI and G/F improved when CV % decreased from 40.5 to 12.1%. However, mortality was not affected by treatment.

The effect of poorly mixed feed on pig performances was reported by Traylor at el. (1994). In this experiment the effect of mix time on diet uniformity and growth performance was evaluated in nursery and finishing pigs on a double-ribbon mixer.

For the nursery experiment, increasing mix time from 0 to 0.5 min decreased the CV % from 106.5 to 28.4% (Table 4). Increasing mix time to 4 min reduced CV value to 12.3%. ADG, F/G and ADFI was increased by 49, 19 and 20 %, respectively as the CV for marker concentration decreased from 106.5 to 12.3%.

For the finishing experiment, increasing mix time reduced the CV for diet uniformity from 54 to less than 10 % (Table 5). The mix time had no statistically significant effects on ADG, ADFI, F/G and bone strength. However, rate and efficiency of gain had numerical increases of 4 and 5 %, respectively, as mix time increased from 0 to 0.5 min.

They concluded that that increased mix time improved diet uniformity and performance of nursery pigs. Finishing pigs were less sensitive to diet nonuniformity, with growth performance being affected only slightly as mix time was increased from 0 to 4 min. The finishing pigs were quite tolerant of CVs of at least 15% and even up to 54%. However, caution is warranted when using a medicated feed article.

Factors That Affect Mixer Performance
Although insufficient mixing time and filling the mixer beyond the rated capacity are often implicated as common sources of variation in finish feed. Other factors such as particle size and shape of the ingredients, ingredient density, static charge, sequence of ingredient addition, worn, altered, or broken equipment, improper mixer adjustment, poor mixer designed, and cleanliness can affect the mixer performance (Wilcox and Balding, 1986; Wicker and Poole, 1991).

The mixing time necessary to produce a homogenous distribution of feed ingredients should be measured for each mixer. Mixing time is a function of mixer design and the rotational speed of the ribbon, paddle, or auger. Each mixer should be ¡ã¡Þtuned¡ã¡À to its proper Revolutions Per Minu (RPM) for optimum ingredient dispersion. Different types of ingredients may have a different flow pattern within a mixer at similar RPM¡ãOs. Generally (Wilcox and Unruh, 1986), the higher the RPM, the faster the more efficient the pattern of dispersion (Figure 1). However, optimum RPM can change over the life of the mixer resulting from normal wear, ingredient buildup or structure basis to allow the mill operator to make the adjustments needed to achieve a high level of operational performance.

The size uniformity of the various ingredients that comprise the finished feed can directly impact final ingredient dispersion (Herrman and Behnke, 1994). If all the physical properties are relatively the same, then mixing becomes fairly simple. As the physical characteristics of ingredients begin to vary widely, blending and segregation problems are compounded. Large and small particles do not mix well and subject to directional influence in nearly any type of mechanical mixer. For example, ground grain with a particle size of 1,200-1,500 microns reduced the likelihood of uniform incorporation of microingredients compared to grain ground to an average particle size of 700 microns (Herrman and Behnke, 1994).

The sequence of ingredient addition also determines ingredient dispersion in the mixing process (Herrman and Behnke, 1994). Mixers may have dead spots, where small amounts of ingredients may not be readily incorporated into the feed. This situation is exasperated when mixing ribbons, augers, or paddles become worn. Ground grain or soybean meal should be the first ingredient added into a horizontal mixer. It has been determined that for the quickest distribution of the microingredients within the mass of major ingredients, the microingredients should enter the horizontal mixer early in the dumping order, no later than 10 seconds after the first of the major ingredients begins its entry (Lanz, 1992).

Overfilling or under-filling a mixer can lead to inadequate mixing (Wilcox and Balding, 1976). Overfilling a mixer can inhibit the mixing action of ingredients in horizontal mixers at the top of the mixer. Filling a mixer below 50% of its rated capacity may reduce mixing action and is not recommended.

The incorporation of liquid ingredients (fats, oils, molasses, liquid chlorine chloride, Alimet and other liquids) into the mixer is a common practice in many milling operations. The best way to introduce liquid ingredients are through a spray bar installed at the top of the mixer. Dry ingredients should be adequately mixed prior to the introduction of liquids into the system. Premature liquid addition tends to impede the transport of micronutrients and may even agglomerate the fine particles into ¡ã¡Þsnowballs¡ã

Most engineers agree that multiple points of application (4-8) are necessary to insure adequate dispersion (Lanz, 1992). The preferred location is such that the manifolds are parallel and located on the ¡ã¡Þup-turning¡ã¡À side of the rotor. Pressure-loaded check valves and air-purged manifolds he minimize the post-spray dripping that can foul the mixer¡ãOs rotor

Mixer Testing
Routine mixer testing should be an integral part of the quality assurance program and should be conducted quarterly. Procedures for mixer testing are relatively simple and involve taking samples at specific time intervals. The assay used and statistical treatment are relatively straightforward.

Sampling
Good sampling is essential for a mixability study to be worthwhile. An analysis is only as good as the sample. The intent of good sampling is to obtain a small portion of a feed that is representative of the whole. One cannot take only the fines or only large particles and expect to obtain an accurate analysis. The eight factors summarized here are important in order to obtain good samples. These apply to all samples and not just to those taken for mixability studies.

Important factors to obtaining good samples 1.Planning 2.Location 3.Quantity 4.Timing 5.Tools used for sampling 6.Containers 7.Proper labeling 8.Sampling preservative

The number of samples to be taken depends on the accuracy of the results desired. Herrman and Behnke (1994) suggested that 10 samples per batch per mixing time would yield sufficient satisfactory coefficient of variance. Eisenberg and Eisenberg (1992) indicate that the number of samples assayed depends mainly upon the laboratory time and costs.

Ideally, samples should be taken within the mixer either at spaced intervals during the mix or on completion of the mix. Sampling within a mixer may be particularly desirable under these conditions: 1.When a mixer design is being studied, an attempt is made to determine where certain ingredients may concentrate. 2.When the effect of time of mixing is being studied, it is not desirable to discharge the mixer frequently or before mixing is complete.

If one cannot take samples from the mixer, then take them as near the mixer in the production system as possible. Frequently if a mixer discharge is being sampled, it is necessary to sample as rapidly as possible at almost uniform time intervals, which may mean taking samples at 5 to 10 second intervals. If poor mixer or segregation is indicated after preliminary trials, it may be desirable to make a special effort to sample from particular locations or at particular times to locate trouble spots.

Recommended Procedure For Sampling Feeds From The Mixer
1.Decide and make arrangements for the analytical work. Obtain equipment and containers for sampling. The suggested size is 100 to 200 gram and sufficient enough for the planned analyses. Mark sample containers for sample identification. 2.Select a suitable location for taking samples preferably as close to the mixer discharge as possible. The site and sampling procedure should not pose a safety hazard to the person involved in taking the samples. 3.Timing the mixer discharge at 8 to 10 samples per batch are recommended, beginning with initial discharge and ending with samples of the tailings at the final discharge. In between samples will be taken at evenly spaced time intervals between the initial and final discharge. 4.Begin sampling sequence when the mixer is ready to discharge. Record the mixing time; mixing time begins when the last ingredient is added to the mixer and ends when the mixer begins to discharge.

Assay Selection
Numerous assay methods have been used for mixer evaluation. However, there is no ¡ã¡Þperfect procedure available. The criteria for the assay selection should be as follows:

1.The assay principals should be based upon a common ingredient, nutrient, or chemical that comes from a single source. Salt, therefore, is a good selection while protein or nitrogen would be a poor selection. 2.The cost of the assay in terms of labor, chemicals, and time should be minimal. 3.The assay procedure should be relatively simple, fast, accurate, precise and should be able to perform in the mill or laboratory, and not require expensive equipment or highly qualified personnel. 4.The assay principle should be supplied from a single source. 5.The sample size required should be reasonable but large enough to reduce or eliminate sampling error. 6.The target mix uniformity (CV values of the tracer) should be about 2 times the proven analytical variation for the assay selected but in no case should it exceed 10%.

Common Mixer Tests Salt (NaCl) is a common component of most livestock and poultry rations. Therefore, sodium (Na) or chlorine (Cl-) ions are often used as mixer test markers. Assaying samples for salt content may be performed using several techniques.

1.Omnion Sodium Analysis (Omnion, Inc., Rockland, Massachusetts): Use a sodium ion electrode to determine the concentration of Na+ in the samples. The percentage of salt can be calculated from these values. The technique appears to be quite accurate and reliable. 2.Quantab? (Environmental Test Systems, Elkart, Indiana): This method determines the chloride ion concentration of a solution. Salt from the feed samples is extracted in hot water. The titrators consist of a thin strip laminated with a capillary column, impregnated with silver dichromate. The column is a reddish-brown color. When the strips are placed in an aqueous salt solution, the fluid will rise in the column. The indicator across the top turns blue, the reaction is completed. Chloride ion concentration is calculated and variation from the expected concentration is used to determine mixer performance.

Color-coded Tracers
Microtracer? Rotary detector (Micro Tracers, Inc., San Francisco, CA 94124): Inclusion and subsequent analysis for tracer particles is another method for mixer testing. A sufficient amount of iron filings, colored with a water-soluble die, is added to the mix to result in sixteen counts (particles) per sample, with the sample size ranging between 50 to 100 grams. The iron particles are demagnetized and sprinkled onto a large filter paper. The filter paper is then moistened with ethanol. When spots begin to develop, the paper is transferred to a preheated hot plate or oven and dried. All particles of the same color are counted, noting the total. Variation from the expected number is calculated to determine mixer performance.

As an interim check, other ingredients such as lysine and liquid Alimet feed supplement can be utilized to help determine if the mixer is functioning within an acceptable range of variation. Feed mills routinely assay for Alimet to evaluate mixability due to its relatively low assay CV (3-5%), and the simplicity of the method which uses High Pressure Liquid Chromatography (HPLC).

Data Analysis
The average marker concentration (mean) and variations between samples (standard deviation) are calculated to arrive at a single value described as the coefficient of variation (CV).

Example: A formula calls for 0.175% Alimet. Determine if a good mix has been obtained.

The mean and standard deviation values can be calculated with an inexpensive calculator with the statistical functions. We conclude from this data that the blend was uniform with a CV value of 2.21%.

Interpreting the Results
A CV of less than 10% has somewhat arbitrarily been used as the ¡ã¡Þcut-off¡ã¡À point for accepting batch of feed as being properly mixed. The industry standard is a maximum CV of 10% for a feed to be considered adequately mixed. Thus, a desirable CV for a well-mixed feed, using the salt assay method, should be at or below 10%. However, variation in the salt assay procedure may be as high as 5 to 6%, indicating that the actual variation due to mixing is about 5%. Furthermore, when using a limited number of samples (10 - 12), it can be expected that occasionally a CV of more than 10% will occur, which may/may not identify an underlying problem in the mixing process. Thus, these figures may be revised to fit individual mill standards and quality control policy.

Conclusion
Feed costs comprise the single most expensive component in producing poultry or other types of meat animals. As a result, effort to reduce nutrient variability within feeds will yield a significant return to commercial operations. Proper ingredient processing and storage, adequate maintenance of mill equipment and routine testing of the final feed are essential to insure optimum animal response to feed nutrients, while controlling feed costs. Nutritionists and feedmill operators should work together to closely monitor feed preparation, and final feed specifications. The bottom-line result will be a reduction in the cost to produce a unit of meat or eggs.

References
Duncan, M.S. 1989. Strategies to deal with nutrient variability In: Recent Advances in Animal Protein Production. Monsanto Latin America Technical Symposium Proceedings. pp. 31-40.
Eisenberg, S and D. Eisenberg, 1992. Markers in mixer testing: closer to perfection. Feed Management. Nov pp 8-20.
Herrman, T. and K. Behnke. 1994. Feed Manufacturing - Testing mixer performance. Bulletin MF- 1172 Revised, Kansas State University Cooperative Extension Service, Manhattan, KS.
Lanz, G. T. (1992) Composition of mixing systems. Novus Nutrition Update Vol 2 (1).
McCoy, R.A., K.C. Behnke, J.D. Hancock and R.R. McEllhiney. 1994. Effect of mixing uniformity on broiler chick performance. Poul Sci 73:443.
Traylor, S.L., J.D. Hancock, K.C. Behnke, C.R. Stark, and R.H. Hines. 1994. Mix time affects diet uniformity and growth performance of nursery and finishing pigs. Kansas State Univ. Swine Day 1994, pp 171-175.
Wicker, D.L. and D.R. Poole, 1991. How is your mixer performing? Feed Manage. 42(9):40-44.
Wilcox, R.A. and J.L. Balding, 1976. Feed manufacturing problems - incomplete mixing and segregation. Bulletin C-555 Revised, Kansas State University Cooperative Extension Service, Manhattan, KS.
Wilcox, R. A. and D.L. Unruh. 1986. Feed manufacturing problems - Feed mixing times and feed mixers. Bulletin MF- 829 , Kansas State University Cooperative Extension Service, Manhattan, KS.

Tags · Optimum Mixability · Mixing · Mixer · Feed Manufacturing

17.02.2008. 13:06