14 min read
Pen of young pigs.

Feed costs can make up 70 percent or more of the operating costs of swine production. To make the most of feed dollars, feed must supply the nutrients required. Unfortunately, feed may have nutritional problems that reduce pig performance. For feed mixed on the farm, many of the problems result from errors in the mixing process. Good feed mixing techniques will ensure the best quality feed and the most economical use of feed dollars.

Mixing swine feed on the farm is much more complicated than many producers realize. You first determine the ingredients to use and the nutrient requirements for the animals you will feed. Next, you need a formula that shows how much of each ingredient is needed to meet the nutrient requirements. Then you mix the ingredients in a feed mill so each pound of feed in a batch is the same. As you can see, there are many opportunities for error. Using the wrong formula, feeding contaminated grain, measuring volume rather than weight, using inaccurate scales, and under-mixing the feed are common errors that reduce the quality of farm-mixed feed. A good feed manager will make sure the feed formulation, ingredients, and mixing techniques are correct and will have a quality control system to find potential problems in the feed.

Quality Control

A quality control program is the first step in making quality swine feed on the farm. Monitor the quality of feed before mixing and before feeding. The key component of a feed monitoring program is routine analysis of feed ingredients before mixing and the final mixed feed. Routine sampling of all feed ingredients and mixed feeds combined with good feed records will improve feed conversion, growth, and feed costs.

Feed Ingredients

The nutrient content of many feed ingredients often varies. The variation can affect both the quality and the cost of the complete feed. To get a good evaluation of feed ingredients, take samples from each load delivered. Take samples before unloading if the ingredients are delivered in bulk. Using a grain probe, take several samples from the front, middle, and rear of the truck, then combine these samples to get a representative sample of that load. If this method is not possible, take several samples while the truck is unloading. Although the combined sample may not be as representative of the load as when a probe is used, it will be better than a single sample.

Sampling each load is best, but the cost of laboratory analysis for each sample can be prohibitive. One alternative is to mix samples from several loads, then submit the combined sample for analysis. It will be impossible to tell anything about a specific load from this type of analysis, but the sample will still aid in fine-tuning the feed formulation. It will also point out problems due to contamination from foreign material such as weed seeds. Check grains for mycotoxins if they are a problem.

The analysis needed for feed ingredients depends on the ingredient. For grains, check protein (lysine, if possible), fiber, calcium, phosphorus, and USDA grade. An official USDA grade includes test weight (an indicator of the energy content), moisture, broken kernels, and foreign material. The same analyses are needed for soybean meal, except for grade. Mineral sources (trace mineral premixes, base mixes, and complete supplements) will come with a guaranteed analysis on the tag. It is a good idea to sample these ingredients and have a complete mineral analysis, including calcium, phosphorus, iron, zinc, manganese, copper, and salt, and crude protein content if it is on the label.

There is a monetary reason for routinely checking purchased ingredients. For example, if you buy soybean meal guaranteed to contain 48 percent crude protein and the analysis shows that it contains only 46 percent, a price adjustment is due. By checking that load, you know to adjust the formulations for the lower protein level and to have the supplier adjust the price.

Mixed Feeds

Routinely analyzing farm-mixed feeds is the only effective way to monitor feed mixing techniques. The method you use to sample mixed feed depends on your reason for the analysis. To determine if the mixing time is appropriate, take three or more samples from one batch of feed periodically as the mill is emptying. If all the sample analyses are close to the same, the mixing time is adequate. For a routine evaluation of the feeding program, use the same sampling technique, but combine all the samples before the analysis to determine if the right amounts of all ingredients were added. If problems exist in certain hog pens, collect feed samples from
each feeder. This last method may not give an accurate evaluation of the mixing process because of separation during delivery and in the feeder.

Every batch of farm-mixed feed and every load of purchased feed should be checked. As with feed ingredients, the cost may be prohibitive. An alternative is to sample each diet mixed or purchased at least once every 3 months and when problems occur. The analysis should include protein, fiber, calcium, phosphorus, iron, zinc, copper, and salt. Amino acid and vitamin analyses would be helpful, but these are often expensive and can be hard to get.

Collecting feed samples and having them analyzed will do little good if the lab report is not accurately evaluated. This report can be used to detect nutritional problems as well as possible causes for these problems. A thorough evaluation of a laboratory analysis by a competent nutritionist can pinpoint problems and, perhaps, solve them.

Feed Records

Another method of evaluating a feed-mixing system is record keeping. The amount of all ingredients used should be the same as the total amount of feed. The records needed to determine this are simple. Record the number of batches of each diet mixed, the amount of each ingredient purchased, and the feed formulations. Keeping these records will also help in evaluating pig performance (feed conversion) and operating costs.

Feed Ingredients

Evaluating feed ingredients can accomplish two things. First, by constantly checking the nutrient content of ingredients, you can adjust some formulas to make the best use of ingredients and reduce feed costs. You can also determine which ingredients, in addition to corn, are suited for your farm. Many alternative ingredients are available for use in swine feed. Some are inexpensive but do not contain the nutrient content and quality of the ingredient being replaced. Others appear to be expensive, but they reduce feed cost when properly formulated. Still others are less expensive than the ingredient to be replaced and have both the nutrient content and quality.

Peanut meal is a protein source some producers use to replace soybean meal. Peanut meal contains more protein than soybean meal, but less than half of the amino acid lysine. Replacing soybean meal with peanut meal on a protein basis can reduce the cost per ton of feed, but will reduce pig performance. The result may be an increase in the cost of gain. Replacing soybean meal on a lysine basis will result in a better amino acid balance, but higher levels of crude protein.

Wheat is often more expensive than corn, partially because of the higher test weight for wheat (60 pounds per bushel versus 56 pounds for corn). If corn costs $6.00 per bushel and wheat costs $6.42 per bushel, the cost is actually equal ($10.41 per hundredweight). Even if wheat is more expensive than corn, it can reduce feed costs. The metabolizable energy content of wheat is the same as for corn (1,500 kilocalories per pound), but wheat contains more lysine (0.30 percent versus 0.24 percent). Replacing corn with wheat in a corn- soybean meal diet decreases the amount of soybean meal needed. The higher cost for wheat may be offset by the decrease in the amount of soybean meal needed.

Grain sorghum is another alternative to corn. The price of grain sorghum is usually 80 to 85 percent of the price of corn. The nutrient content of grain sorghum is similar to that of corn. On average, grain sorghum contains 9.2 percent protein, 0.22 percent lysine, and 1,425 kilocalories of metabolizable energy per pound. Corn contains 0.24 percent lysine and 1,500 kilocalories of metabolizable energy per pound. Replacing corn with grain sorghum may increase the feed required by 5 percent, but it costs 15 to 20 percent less than corn. The result is a decrease in the cost of production even though the amount of feed required may increase.

Commercial products are often difficult to evaluate because the feed tag supplies the information on the product. By law, the tag must include a guaranteed analysis, a list of ingredients, and instructions for feeding. Unfortunately, there is often too little information on the tag for a thorough evaluation. Complete supplements are the most difficult to evaluate because of their complexity. A complete supplement should complement the grain used by supplying amino acids, calcium, phosphorus, salt, trace minerals, and vitamins. Because of the increased use of synthetic amino acids, supplements are even more difficult to evaluate. The supplement tag will provide some of the information required for evaluation; however, the producer using a complete supplement must rely on the manufacturer for additional information.

Typically, commercial base mixes should supply the calcium, phosphorus, salt, trace minerals, and vitamins not found in adequate amounts in the grain and soybean meal. Using a commercial base mix requires trust in the manufacturer. The products are normally developed to go in to a corn-soybean meal diet. Many contain additives designed to enhance naturally occurring nutrients (for example, phytase) or pig performance. Make sure the company representative knows exactly what ingredients you plan to use and the weight, class, and type of pigs you raise. You must rely on the manufacturer for nutritional information not on the label and for assistance formulating diets using commercial base mixes. A competent nutritionist can help you evaluate commercial products for your feeding program.

By considering cost and nutrient content, you can better evaluate alternative feed ingredients. Computerized diet formulation combines ingredients to produce the cheapest possible diet that meets all nutrient requirements.

Feed Formula

Feed formulas used on most swine operations come from three sources: feed tags, consultants, and university Extension or research. Formulas from feed tags are general. They often list grain rather than specific grains such as corn, wheat, and grain sorghum. These formulas contain a safety margin to reduce the problems caused by below-average nutrient content in an ingredient.

Most other formulas are specific, not to one grain, but to one load of that grain. These are based on the analyzed nutrient content of each ingredient to be used. Specific formulas should meet the pigs’ requirements with little or no margin for error.

A formulation for a specific class or weight of pigs must be used for those pigs only. For feed company recommendations, follow the instructions on the feed tag as closely as possible. Only use a feed ingredient designed for one class of pigs at a specific rate per day as it was intended.

A common practice is to add ingredients that are not in the formula. Any nonnutritive additives such as antibiotics should not cause any problems. Adding other products such as mineral mixes can result in a poor finished product. The producers who think their hogs require more nutrients or higher levels of some nutrients than a commercial product or a custom formula supplies should find another commercial product or formula that better suits their needs.

To ensure that feed formulations are not causing problems on your farm, keep these points in mind:

  • Make sure the formulation being used is designed for and meets the needs of the animal being fed.
  • If using a supplement, follow label instructions exactly. Do not change the amount of supplement called for.
  • If using a base mix, substitute ingredients only if the nutrient content or cost of ingredients change. Then have the changes checked by a competent swine nutritionist.
  • If using a custom formulation, make sure the formula is changed as the available ingredients and nutrient analyses change.

Processing and Mixing Methods

Common feedstuffs must undergo processing to ensure the best use in swine diets. Processing may alter the physical or chemical nature of the nutrients, allow more uniform mixing of ingredients, or reduce waste of feed by the pig. This may improve feed intake or digestion and absorption of feed nutrients. The result should be economical improvements in rate of gain or feed efficiency.

Grains and other feed ingredients may be processed in many ways. Grinding is the most common. In recent years, the use of rolling, roasting, and extruding have increased. High moisture processing and pelleting are also used in processing swine feeds.


Grinding with a hammer mill is the most common method of processing grains. Grinding improves the feeding value of most grains. It also improves the mixing qualities of grains and assures intake of a balance of diet ingredients. The initial cost of a hammer mill is lower than most other processing methods, even though the cost of operation may be higher.

Different feedstuffs require various degrees of grinding (fine, medium, coarse). A finer grind can improve feed efficiency in corn and grain sorghum but very fine grinding may lead to gastric ulcers. Fine grinding of wheat results in a powdery, dusty diet that is undesirable. Performance of growing and finishing pigs fed coarse-ground wheat is superior to those fed fine-ground wheat.

The particle size of a grain processed in a hammer mill depends on three factors. The size of the openings in a hammer mill screen will partially determine particle size. The speed of the hammer mill also affects particle size. Particle size increases as the speed of the mill (rpm) is decreased. Particle size also increases as the the flow of grain into the mill increases. For most grains, screen opening diameters in the range of 1⁄8 to 3⁄8 inches will provide proper grinding.


Roller mills may be used for the following:

  • Roll or crimp dry grains
  • Roll steamed or high moisture grains
  • Flake-steamed grains (steamed longer and rolled with more pressure)
  • Crumble pelleted feeds to improve intake in certain instances

Processing grains with a roller mill may produce a product similar to grinding but results in a more uniform final product. Roller mills are generally more expensive than hammer mills but cost less to operate. Because of the added cost of steam, dry rolling is typically more economical than steam rolling or steam flaking for most diets.

Rolling is the best processing for wheat and oats under most situations. Very lightly rolled (crushed) wheat appears to improve feed intake and gains compared to ground wheat when fed to pigs heavier than 40 pounds. Rolled oats are desirable in some baby pig diets.

Roasting and Extruding

Roasting and extruding are used primarily to process soybeans. Raw soybeans contain toxic compounds that reduce pig performance. Soybeans must be heated to destroy these compounds. The ideal cooking time and temperature depends on the equipment and moisture content of the soybeans. Heating soybeans at 270 degrees to 300 degrees F for 2 to 5 minutes to an exit temperature of 245 degrees F (240 to 260 degrees F is acceptable) is adequate to destroy the toxins in soybeans.

Roasters use an external source of heat, usually gas. Extruders use heat generated by the soybean kernel. Extruders subject soybeans to extremely high pressure, creating heat. An exterior source of heat is often used as a precaution. Both methods do an adequate job of processing soybeans. The availability of amino acids is similar, as is the performance of pigs fed extruded or roasted soybeans. Roasters are usually less expensive than extruders but may cost more to operate.

Some data suggest an improvement in pig performance from roasting grains (such as corn or grain sorghum). Before purchasing a roaster for grain processing, however, the improved performance must offset the cost of processing.


Researchers do not completely agree on the benefits of pelleting swine diets. Improvements in feed efficiency range from 3 to 10 percent with a 5-percent improvement being a reasonable standard. Improved digestibility of nutrients and reduced feed waste account for the improved efficiency. Improvements in rate of growth from pelleting of diets have been inconsistent but may be as much as 3 to 6 percent. Pellet size and quality (firmness) may determine if pelleting feed is a viable option. A firm 3⁄16-inch pellet appears to be ideal for growing and finishing pigs. Small pellets or crumbling of large pellets may result in greater intake of baby pig diets. Greater advantages of pelleting appear to result when using certain diet ingredients (such as barley and wheat middlings).

High Moisture Processing

High moisture processing has limited benefits from a strict nutritional viewpoint. High moisture grains show slight advantages in phosphorus availability and protein digestibility. Higher processing and storage costs must be offset by improved harvesting efficiency and elimination of grain drying costs. High moisture harvested grains must be ground or rolled before mixing and feeding.

Other Processing Methods

Other processing methods such as micronizing, popping, and exploding have limited applications to swine diets because of lowered effectiveness or higher costs.

Feed Mixing Procedures

Good mixing begins with an understanding of the equipment used. Feed mixing equipment can be divided into two broad types: continuous and batch. The continuous mixing systems used on swine farms are metering mills. These mills meter ingredients into a mixing auger in set proportions. Batch mixing systems mix a set amount depending on their capacity. Most continuous systems are stationary, while batch systems can be stationary or portable. Mixing procedures are totally different for batch and continuous systems.

Continuous Mixing Systems

The big advantage of a continuous mixing system is its automatic operation. Once you start the mill, it mixes until it runs out of ingredients, fills a finished feed bin, or is turned off. The main unit of this system is the proportioner, which controls the volume of each ingredient added. This proportioner must be routinely calibrated for the proper mix. Changes in ingredient density (that is, changes in test weight) will change the proportions by weight and therefore the nutrient content of the mix. For example, if you calibrate a mill for corn weighing 56 pounds per bushel, and the next load of corn weighs only 54 pounds per bushel, the diet that should have 1,700 pounds of corn only contains 1,640 pounds.

These mills are calibrated by two simple methods. The first method consists of weighing the amounts of each of the ingredients being metered in simultaneously. Place a weighed container under each ingredient auger. Divert the ingredients into the container, then run the mill. When you collect an ample supply of the least ingredient (5 to 10 pounds), turn the mill off. Weigh each ingredient, then subtract the weight of the containers. Add the weights of each ingredient together, then divide that number into 2,000. This gives a factor to use in correcting the amounts collected to a ton basis. Multiply this correction factor by the weight of each ingredient collected. The resulting number is the amount of that ingredient being added to a ton of feed.

Compare the amount per ton for each ingredient with the formula and make needed adjustments.

The second method works best when there is a wide range in ingredient levels. Run each ingredient for the same length of time. When each ingredient has been collected, determine the weight of the ingredient less the weight of the container. Add the ingredient weights and divide into 2,000 (same correction factor as above). Multiply each weight by the correction factor. This gives the diet formula in pounds per ton.

In both cases, the adjustments depend on the make and model of the machine. The adjustments needed are in the owner’s manual. If one is not on the farm, contact the equipment dealer or company representative.

Continuous mixing systems are only as good as the operator. Every part of the system must be working properly to produce quality feed. You must carefully calibrate the mill, analyze samples of mixed feed, and frequently check the system to produce quality swine feed.


Amounts collected:

  • 5 pounds of basemix
  • 55 pounds of corn
  • 40 pounds of soybean meal.

Total collected = 100 pounds

The feed formula is for 2,000 pounds, so divide 2,000 by 100 for a conversion factor of 20. Multiply the weight of each ingredients collected times 20 to get the amount per ton:

5 pounds bas mix                x   20 = 100

55 pounds corn                    x   20 = 1,100

40 pounds soybean meal   x   20 = 800

100  +  1,100  +  800  =  2,000

Batch Mixing Systems

Batch systems take more time but generally are more accurate because each ingredient is weighed. Vertical mixers are more popular than horizontal mixers because they take less space. Horizontal mixers typically provide a better mix and have a shorter mixing time. Some stationary systems combine both a horizontal mixer for combining ingredients used in small amounts and a vertical mixer for mixing the complete feed.

The mixing accuracy of a horizontal mixer is because of its mixing action. Horizontal mixers have one of two mixing mechanisms: a ribbon (Figure 1) or paddle (Figure 2). Both will provide a good mix, but the ribbon provides a more uniform final mix.

The chances for mixing errors are usually greater when using vertical mixers. Figure 3 is a simplified drawing of a vertical mixer at work. Ingredients enter the mixer, are carried to the top, and drop into the mixing area. This action makes it difficult to properly mix ingredients added in small amounts (40 pounds per ton or less). Blend these ingredients with another ingredient (such as grain or soybean meal) before mixing.

Because of the design, 10 to 20 pounds of the first ingredient added to the mixer may never be mixed because the mixing auger never picks it up. Two additional steps to the process solves this problem. First, avoid adding ingredients used at 200 pounds or less to an empty mixer. Then, just before mixing is complete, auger out about 50 pounds and put it back in the mixer. These two practices will reduce the chances of a feeder being filled with straight premix, base mix, soybean meal, or other ingredients.

Portable mixers and stationary mixers in some conditions pose other problems. It is tempting to weigh all ingredients except the grain, put them in the mixer, and then fill the mixer with grain. It is impossible to measure weight by measuring volume in grain. Another problem is running the mixer until the grain is ground and then shutting the mixer off. The feed must mix at least 5 minutes after the last of the grain is in the mixer. For most mixes, the time should be 7 to 10 minutes, depending on the model of the mixer and the amount of feed being mixed. Overmixing can lead to feed separation in some farm conditions. More importantly, it increases the amount of fuel or electricity used, therefore increasing the cost of mixing.

Still another problem is scales. Many portable mixers do not have scales. Scales are expensive ($300 to $3,500) and require frequent maintenance. However, the cost of scales is more than offset by the improved quality of feed when scales are used. Balance manual and electronic scales frequently. Scales for portable mills are designed for rough conditions, but they are still delicate instruments. Check the accuracy by adding a known weight of ingredients. If scales are not weighing accurately, have them repaired.


Any feed mixing system is as good as the effort going in to it. Use the following steps as a guide for evaluating your own system. Even a slight improvement in feed quality could mean savings in feed costs.

  1. Follow instructions on feed tags or formulations exactly.
  2. Have ingredients analyzed regularly.
  3. Have formulations adjusted by a competent nutritionist as the nutrient content of ingredients or the ingredients themselves change.
  4. Compare ingredient costs and feeding value before buying a cheap ingredient.
  5. Routinely calibrate the proportioner (metering mill).
  6. Keep all feed handling equipment (mixers, augers, bins, and feeders) in good repair.
  7. Weigh all ingredients before mixing (batch system).
  8. Avoid undermixing and overmixing.
  9. Sample and analyze feeds regularly.

Doing the best job possible when mixing feed will ensure the best possible feed for your pigs.

Reviewed August 2021, Controlling Quality of Farm-Mixed Swine Feed, ANR-0637

Did you find this helpful?