(Table of Contents)

Grinding is the most common method of feed processing for the swine producer and nearly all feed ingredients will be subjected to some type of particle size reduction. Particle size reduction increases the surface area of the grain, allowing for greater interaction with digestive enzymes, improving feed efficiency. It also improves the ease of handling and mixing characteristics. However, fine grinding will increase the energy costs of feed processing and may result in the feed bridging in feeders and bulk bins. increased dustiness, and the potential for gastric ulcers. Therefore, the increased costs of fine processing must be offset by the resulting improved feed conversion.

What is the optimum particle size?

Confusion exists concerning the optimum particle size of swine diets because of broad classification like "fine, medium, and coarse," used to define particle size. In addition, different grains, because of their kernel size and shape, will produce a different particle size when ground through the same screen. At present, considering improvements in feed efficiency, processing costs, incidence of gastric ulcers, and potential for bridging, an average particle size of 700 to 800 microns is recommended.

In addition, fine (700 microns) grinding of high-fiber feed ingredients has been shown to improve their feeding value. As a rule of thumb, if there are whole kernels in your feed, it is probably not ground fine enough,a nd you may be losing 5 to 8 percent in feed efficiency. Results of over 1,500 samples analyzed at Kansas State University since 1985 indicate that 70 percent of the samples are over 800 microns in particle size.

Should I process my feed with a hammermill or a roller mill?

This is one of the most frequently asked questions concerning particle size reduction. Either mill is capable of producing the desired particle size. However, there are advantages and disadvantages that must be considered to determine the best mill for your operation. Hammermills have greater capacity per unit horsepower, and it is easy to change from grinding one grain to another by changing screens. However, a hammermill requires more energy than a roller mill and will produce a higher percentage of fines and dust.

A roller mill requires about 28 percent less energy to produce a 700-micron particle size than a hammermill, but if grain types are to be changed frequently, the roller mill will need to be adjusted for each grain. For processing grain with a hammermill, screen size will vary based on type of grain. Corn and wheat may be processed through a hammermill equipped with a 3/16-inch screen, whereas a 1/8-inch screen is recommended for processing milo, barley, and oats. By using these screens with the respective grain, a 700- to 800-micron particle size should be achieved.

Condition of screens and rollers will be critical in grinding efficiency and maintaining optimum particle size. Screens and hammers need to be checked at least monthly for wear and replaced if there are holes in the screen or if the holes become funnel-shaped. Hammers can also be reversed or replaced if they become worn.

In roller mills, three criteria are essential in producing a 700- to 800-micron particle size: (1) the rolls should be moving with a differential drive of one roll moving 50 to 75 percent faster than the other to produce a shearing action that will help "cut" the kernel rather than crush it; (2) the rolls should have corrugations to help slice the grain, with the desired corrugations per inch of roll being 8 to 10 for corn, 10 to 12 for wheat, barley, and oats, and 12 to 14 for milo; (3) the corrugations should have a 1- to 2-inch spiral to increase the shearing potential and eliminate fines. Magnets are important to remove any metal objects from the grain and increase the longevity of hammers, screens, and rollers. Both hammermills and roller mills should be checked periodically for wear.

How beneficial are other processing methods?

There are many different methods for processing feed for pigs. In addition to grinding, the most common forms of feed processing are pelleting, extruding, and roasting.

Pelleting. Pellets can be made of different lengths, diameter, and degree of hardness. The ingredients of the diet will influence the hardness of the pellet and pellet quality. Various studies suggest a 3 to 10 percent improvement in growth rate and feed efficiency when pigs are fed pelleted diets rather than a meal. This appears to result from less feed waste with pelleted feeds. Pelleting appears to improve the nutritional value of high-fiber feed ingredients to a greater extent than that of low-fiber ingredients. This may be a result of increasing the bulk density of the feed. However, as energy costs increase, the economics of pelleting swine feeds may be change. The increased diet cost must be offset by the improved feed efficiency or other productive measure of pigs fed the pelleted diet. Of future importance is the potential benefits that pelleting produces by sanitizing the feed. This aspect has yet to be examined in swine production and may play an intergral part in future production systems.

Extrusion and Roasting. Extrusion processing involves the application of heat, pressure, and (or) steam to an ingredient or diet. Extruders are sometimes used for on-farm processing of soybeans. If properly heated, this is an easy way to add fat to swine diets and utilize home grown soybeans. Recent research shows that moist, extruded, soy protein concentrate is an excellent protein source for baby pigs.

Because of volume and tonnage, extrusion of complete feeds is usually not economically justified based on performance of pigs fed extruded complete feeds. Furthermore, extrusion increases the bulkiness of the diet, making it more difficult for the pig to consume enough feed to meet its nutrient requirements.

Roasting can also be used to process home-grown soybeans. This can also be an alternative method for adding fat to swine diets. However, roasting temperature and times must be checked to ensure adequate processing. The added cost of the extruded, or roasted products must be the ultimate consideration in determining the feasibility of their use in swine diets.

Other Processing Methods. Several alternative processing methods are available to swine producers. Steam flaking, micronizing, and other processing methods often do not improve pig performance enough to justify the added expense of processing. When evaluating the expense of feed processing methods, the following equation will determine if it is justified:

percent improvement in feed efficiency needed to offset added diet cost

What is the feeding value of high-moisture grains?

High-moisture grain is similar in feeding value to regular grain on a dry matter basis. Rate of gain and feed efficiency, when compared on an equivalent dry basis, have been essentially the same for pigs fed high-moisture or dry grains in a complete diet. Some studies with high-moisture grains and free-choice supplement have indicated that under- or over-consumption of protein supplement is a problem. It is recommended that high-moisture grain be included in a complete ground and mixed diet. The amount of supplement needed for proper diet formulation is influenced by the amount of moisture in the grain (Table 15).

The use of high-moisture grain in a swine feeding system is an economic decision rather than a nutritional one. Although using high-moisture grain adds flexibility in timing of harvest and eliminates the need to dry grain, storage facilities can be costly and management to prevent spoilage is critical. Fresh feed must be mixed every 1 to 2 days to prevent spoilage of the mixed feed in the feeders. Thus, the various costs involved should be carefully studied for each individual case before a sound decision can be made.

If you plan to use an organic acid preservative, the high-moisture grain should be treated as soon as possible after harvest, especially during warm weather. Rate of acid application varies with the moisture content of the grain and the intended length of storage. The higher the moisture content of the grain, the greater the amount of acid needed for proper preservation. Table 16 gives the recommended rates for 100 percent propionic acid for a maximum storage period of 1 year. These rates are listed for corn, but would be suitable for other grains. The acid application preserves the grain by inhibiting mold growth. The acid reduces the Ph of the grain below the mold requirement and also kills the grain germ.

Can I mix my own fed on the farm?

As outlined in the introduction of this guide, swine producers have several options for mixing feed. In general, there is a trend towards taking more of the responsibility for mixing feed. This generally lowers feed costs and increases the flexibility a producer has in mixing several different diets, but more time, labor, and facilities will be required.

Probably the biggest concern is that the producer must now take on the added responsibility of quality control to ensure a properly formulated and mixed diet. It is difficult to determine the size of operation for which it is profitable to assume mixing and formulation responsibilities. This will also vary with the preference and goals of the producer.

A commonly suggested tonnage at which one should consider replacing purchased complete feed or supplements with soybean meal and base mixes or premixes is between 500 to 750 tons per year. To calculate the distribution of your feed costs, it is estimated that a sow and her pigs (assuming 18.5 pigs per year) will require 7.3 tons of feed per year. This includes boar feed as well. Of that 7.3 tons, the feed will be distributed as follows:

Diet% of Total
Starter I1 percent
Starter II2 percent
Starter III3 percent
Grower I13 percent
Grower II20 percent
Finisher45 percent
Gestation10 percent
Lactation6 percent

By multiplying your present feed costs per phase by the projected tonnage, you can quickly see where the bulk of your feed dollars go. This often helps to determine the cost comparison between feeding programs. Comparing these values to your actual usage is also a useful diagnostic indicator to see if you are feeding the correct feed for the correct period of time, i.e., not overfeeding one phase and underfeeding another.

In addition to particle size reduction, the producer must also be concerned about whether or not the feed is being mixed properly, and ingredients must be accurately weighed. A preferred way to accomplish this is with a gravimetric scale, rather than a volumetric meter. If a volumetric meter is used, it must be recalibrated often, because bushel weights change frequently. With a premixing system, only scaled, batch mixing operations, not volumetric mills, should be used.

Mixers and mixing time vary considerably. Mixing times for horizontal mixers are approximately 5 minutes. Worn ribbons or paddles will increase the time necessary to adequately mix a batch of feed. Vertical mixers and on-farm grinder-mixers generally required approximately 15 minutes to mix a batch of feed. Tests have shown that over-filling mixers greatly increases the amount of time needed for mixing. Worn ribbons and screws will also contribute to increased mixing times. Very often, manuals underestimate the amount of time necessary for feed mixing.

A mixing test is a sure way of knowing the correct mixing time for your mixer. Mixing efficiency can be measured by taking several samples of feed from one batch cycle and analyzing them for salt content. The variation between samples in salt content is used as an indicator of properly mixed feed (10 percent). If feed is under-mixed, this will be more of a problem for young pigs because they eat only a little feed. Larger pigs, however, by virtue of their greater feed intake, may be less susceptible to marginally mixed feed.

The sequence in which feed ingredients are added to a mixer may influence mixing efficiency and feed uniformity. Ingredients should be added in the following order: (1) half of the grain; (2) protein sources, vitamins, minerals and feed additives; (3) the remainder of the grain.

Can I over-mix feed?

There is a common misconception that feed, if mixed too long, can become "unmixed." Tests indicate that feed reaches a "steady state" of being mixed and remains at or near that point for an extended period of time. However, during transportation of mixed feed or ingredients it is possible that segregation of ingredients may occur.


How can I monitor quality control?

As you assume more responsibility for mixing your own feed, quality control will be vital to avoid use of inferior feed ingredients. A stringent and tough quality control program will help in this effort. Quality control programs will vary based on the size of the operation and tons of feed used. However, the following is a suggested program indicating the items to check and how often. These are only suggestions, and you may check them more or less frequently as you see fit.

Particle size. Based on the tonnage processed per year, particle size should be checked very 400 to 500 tons of feed processed. If you notice whole kernels or even half kernels, these can be indicators of a hole in a screen or worn hammers or rollers.

Mixing efficiency. Mixers should be checked for proper mixing times when they are first installed, then updated periodically as screws, augers, and paddles become worn. This can be once every year or two, depending on tonnage mixed.

Grains. Moisture content and test weight will be most critical as indicators for determining grain quality. In addition, foreign materials and presence of molds or other contaminants that can occur because of improper storage should be noted. A moisture tester and a blacklight (for aflotoxins) can be practical means for on-farm testing of grain quality. Protein content can also be checked to determine quality.

Soybean meal. Soybean meal is the most common protein supplement used. Standards are established for protein, fiber, moisture, and calcium. The purchaser is entitled to price adjustment should these criteria not meet set standards. However, this price adjustment does not happen automatically. The producer must have the soybean meal analyzed and request a price adjustment.

When purchasing a new load, request an official sample and ask the company for a written description of the content. Then send the sample to a refereed analytical laboratory for analysis. You may decide to take a duplicate sample for analysis when it is unloaded. Generally, 48.5 percent soybean meal will have less fiber and be a more consistent protein source than 44 percent soybean meal. Other protein sources are often variable in nutrient content and should be analyzed for protein content as an indicator of amino acid content. This variation is often a hidden cost of using alternative protein sources.

Whey and fish meal. Because these ingredients are often added to baby pig diets, quality is essential. Specify "edible grade" dried whey and "select menhaden" fish meal. These producers often have excellent and predictable nutrient quality.

Dicalcium phosphate and limestone

A common problem for producers is formulating their diet with dicalcium phosphate (21 percent Ca and 18 percent P) and buying monocalcium phosphate (18 percent Ca and 21 percent P). Always check feed tags and ingredient labels.

Complete supplements, base mixes, and vitamin and trace mineral premixes. Check periodically for certain nutrient content. Generally, this will include screening for two to four nutrients and rotating the nutrients checked with each batch. Check the more expensive nutrients such as protein, phosphorous, vitamin E, and riboflavin.

Fats and oils. Rancidity may be the biggest problem with fat and oil sources. If questionable, check for free fatty acids and MIU (moisture, impurities, and unsaponafiable material). A high quality fat source is essential in formulating swine diets.

When storing fats or oils for long periods of time, stabilize them with an antioxidant, such as ethoxyquin, BHT, or BHA.

Complete diets. If a stringent quality control program is followed on all incoming ingredients and processing, there should be little need to check the final product. However, periodically checking one or two of your diets on a rotational basis is a good way to double check your system. Check for moisture, protein, and possibly calcium and phosphorus.

The preceding items are typically the more expensive nutrients and are most likely not to exceed minimum requirements.

What steps should I follow to ensure diet quality?

Fill out a diet formulation sheet, including prices and as much diet content information as possible. Feed tags and a complete ingredient description should be included when possible. These records can provide important historical information about your operation's feeding program.

Check your calculated nutrient composition and compare it to those suggested by North Carolina State University.

Check your diets frequently. Again, check the tonnage used by each phase of production to make sure you are not over-feeding a diet. Also, continually check prices of your diets and cost per cwt of pork sold.

How do I take a good sample?

Nutrient composition can vary within each specific batch of feed to such a degree that chemical composition can be significantly altered based on a non-representative sample. A composite sample that is representative of the complete batch mix is the key to successfully determining nutrient concentrations. Sampling is a step-wise procedure that must be scrutinized heavily to ensure that proper samples are obtained. First, identify the most practical method of sampling based on the mixing system, feeding program, and the purpose of the sample.

Samples taken to determine mixing efficiency are not composite and must be analyzed individually, whereas samples taken to determine crude protein, calcium, amino acids, etc., must be composite to determine average composition. Thus, the first step is identification of sampling location. The following locations are acceptable for obtaining samples:

Mixer. Samples can be taken using a grain trier/probe from separate locations within the mixer; approximately 10, 1-lb samples should be taken and combined into one composite sample for chemical analysis or kept separate for mixing efficiency tests. The most common method of sampling a mixer is to obtain 10 samples at the discharge outlet while unloading the mixer. Take care to avoid sampling the initial output as well as the final output, because these can be extremely variable.

Bulk feed. Take samples during the loading or unloading process and at timed intervals to ensure a representative sampling. Use an in-line, automatic sampler while moving the product to a bin or while loading a truck or car. However, grab samples may be obtained while unloading the product at the destination. The samples can be combined for chemical analysis or kept separate for mixing efficiency tests.

Sacked feed. Samples should be obtained using a bag trier/probe. Samples taken by hand, with a cup or with a dipper, are most common, but often fail to provide the best possible sample. Ten, 1/2 lb samples should be obtained, but deviation may be necessary depending upon the number of sacks in the lot. The bag should be laid horizontally and probed diagonally from end to end. From lots of 1 to 10 bags, sample all bags; and from lots greater than 11 bags, sample 10 bags. Samples should be combined for chemical analysis and are probably not best used for mixing efficiency tests.

What kind of variation can I expect in lab analyses?

Variation is calculated nutrient concentrations and actual analyzed values are affected by many factors. Some of these include: sampling error, inadequate mixing, inadequate calibration of scales or volumetric mixers, and storage losses. In addition. certain tolerances are allowed for accuracy of specific lab analyses. The 1990 official publication of the Association of American Feed Control Officials lists the following analytical variations as guidelines for helping officials make routine decisions on acceptability of feed ingredients.

Table 1. Analytical Variation

Item            %               
Moisture        12              
Protein         (20/x + 2)      
Fat             10              
Fiber           (30/x +6)       
Calcium         (14/x + 6)      
Phosphorus      (3/x + 8)       
Riboflavin      30              

In these examples, x equals the percent guarantee, i.e., if the protein guarantee is 10 percent, the analytical variation is 20/10 + 2 = 4 percent. This means that the sample must contain between 9.6 and 10.4 percent protein to be acceptable. Analytical variation is not reported for amino acid analysis, but variation from 20 to 30 percent can be anticipated.

Will having feed chemically analyzed aid in diet formulation?

Yes, because individual feed ingredients will vary testing results will aid in diet formulation. An alphabetical list of commercial analytical laboratories appears in Table 17. This listing is for information only and does not constitute an endorsement of the labs listed nor a discredit to any lab inadvertently omitted from the list. Contact the lab of your choice for a price list and for instructions on size of sample, sample methods, and mailing.

What is an open formula?

An open formula is a listing of ingredients and nutrient concentrations supplied in a complete feed, protein supplement, base mix, or premix. This information is listed on the feed tag and readily available to the producer. It can be used to compare prices based on nutrient specifications to ensure that they meet the pig's requirements. Closed formulas do not provide nutrient specifications, making it virtually impossible to determine cost/unit nutrient or the nutrient levels provided in the diet.

To make sound economic and management decisions concerning feeds and feed ingredients, the use of open formulas in swine diet formulation is strongly encouraged.

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