Mixing your own swine feed

Quick facts

  • When you mix and formulate your own feed, you are responsible for maintaining feed quality.
  • Quality control is needed from the time you purchase feed ingredients to the time the pigs eat it.
  • Feed costs represent 60 to 70 percent of the total cost to produce a market hog making quality control key to successful production.

Mixing most or all of your feed makes you responsible for quality control. Quality control aspects of on-farm feed mixing often receives little attention. The National Pork Producer’s Council developed the educational program “Pork Quality Assurance” with instructions on producing wholesome pork.

  • Researchers at Michigan State University found that 33 percent of feed samples vary more than 1 percent from desired crude protein levels.
  • Ohio State University found that only 20 percent of the sampled sow diets met or exceeded the sow’s nutrient needs for crude protein, calcium and phosphorus.
  • Thirty-four percent weren’t mixed or sampled properly.

Such errors in feed can have an economic impact on swine producers. Workers at Purdue University found when protein rises above 15 percent, feed costs increase but performance doesn’t improve in market hogs. Low-protein diets resulted in depressed average daily gain, poor feed efficiency and high production costs.

These results show the importance of quality control when mixing your own feed. The following tips can help you achieve quality control.

Use high quality ingredients


  • Make sure all grains are free of molds, insects, dirt, stones and other debris.
  • Avoid using a high proportion of broken kernels.
    • Broken kernels more likely support mold growth than intact kernels.
  • Make sure the grain is about 12 to 15 percent moisture for safe storage.
  • Avoid temperatures over 300 degrees F when artificially drying grains.
    • Overheating can harm protein quality.
  • Protect the grain from rodent damage and mold contamination while in storage.
    • Rodents will eat the grain and contaminate it with droppings leading to reduced grain palatability by pigs.


High moisture in stored grain enhances mold growth. Molds produce toxins that depress pig performance. A presence of mold doesn’t mean toxins are present. Commercial laboratories can test your grain for mold toxins. These tests cost between $25 and $50. There are some mold toxin tests available for on-farm testing.

The following molds are known to harm pig performance.

Aflatoxin contamination

Aspergillus flavus produces the toxin aflatoxin. Aflatoxin is a carcinogenic compound that causes anemia and stunted growth in pigs when present at 200 parts per billion.

The Food and Drug Administration guidelines allow no more than 20 parts per billion of aflatoxin in animal feeds.

Aflatoxin contamination of grains is not a common problem in the North Central U.S.

Fusarium molds

Fusarium molds produce the toxins zearalenone and vomitoxin.

  • Zearalenone at levels over 1 part per million has estrogenic properties that will cause swelling of the vulvas and teats of young gilts.
  • Vomitoxin causes feed refusal when present at 0.5 parts per million. Vomiting will occur at much higher concentrations of vomitoxin.

Fusarium molds commonly occur in grains, primarily corn. You can identify fusarium mold by white to pink discoloration of grain.

You can use young gilts to do a preliminary test for Fusarium toxins. Feed the suspect grain to young gilts (100 to 125 pounds) and observe feeding behavior and anatomical changes.

  • Feed refusal or low intake suggests a vomitoxin presence.
  • Normal feed intake but swollen vulvas and mammary systems after two to three days suggests a zearalenone presence.

You must submit samples to a lab for confirmation and to know the quantity of toxin present in the grain.

You must store protein supplements under the same conditions described for grains. The protein must be free of contaminants. Most soybean meal is produced by companies that follow the National Soybean Processor Guidelines and meets the established quality standards.

Soybeans processed on the farm

Producing a high quality protein source is harder when processing soybeans yourself. You must subject the soybeans to the proper time and temperature to destroy any antinutritional factors present. You must do this without reducing protein quality.

  • Heat roasted soybeans for three to five minutes at 240° to 260° F
  • Extruded soybeans should have an exit temperature of 280° F

Underprocessing won’t destroy all of the trypsin inhibitors or urease enzymes. You can use urease enzymes as an indicator of proper processing. You can test for underheating by combining the following in a small plastic bag:

  • 1 part urea
  • 5 parts water
  • 10 parts soybean meal; extruded soybeans; or ground, roasted soybeans

Close the bag and wait 30 seconds. If the soybeans are undercooked, the urease in them will convert urea to ammonia. You can detect ammonia by smelling near the open bag. Properly processed soybeans won’t produce ammonia.


Overheating soybeans or soybean meal will damage the proteins within these soybean products. Damage to proteins reduces the availability of essential amino acids, particularly lysine, to the pig. Overheated soybean meal or soybeans have a color ranging from tan to dark brown, depending on the severity of overheating.

Most swine producers don’t have the proper equipment to produce high quality premixes. Commercial manufacturers have the proper equipment and technology to blend vitamins and trace minerals together while protecting the potency of vitamins.

  • Purchase vitamin and trace mineral premixes from commercial companies.
  • Trace minerals can easily harm the potency of vitamins if not properly mixed.
  • Use vitamin-trace mineral premixes within 90 days of purchase.
  • Potency of premixes decreases with long-term storage.
  • Store premixes in a cool, dry and dark place.

How to mix and store feed

Accurate formulation makes sure the diet meets the needs of the specific pig.


Nutrient content of feed ingredients can vary greatly from the average values listed in nutrient composition tables.

  • Low-yielding, drought-stressed corn usually has higher protein content than what’s published in nutrient composition tables.
  • High-yielding corn may have a lower protein content than what’s listed in published tables.

The most accurate formulations result when laboratory analysis of ingredients is available. Seek the help of trained professionals if you aren’t comfortable calculating the formulations.

When using a recipe from feed tags or special formulations, follow it exactly. If you alter the recipe, the nutrient content of the final feed will also change and could harm pig performance.

Only use supplements and premixes that have been formulated specifically for swine. Don’t use a trace mineral premix designed for beef cows in a sow diet.

Don’t mix premixes and supplements from different suppliers. For example, don’t use company A supplement with company B booster pack. Products from different companies aren’t made to go together in a diet.

You must process cereal grains through a hammermill or roller mill to reduce particle size. Reduced particle size is key to achieve optimal pig performance.

  • Smaller particle size makes the feed easier to digest.
  • Smaller particle size improves the efficiency of body weight gain.
  • Smaller particle size allows for uniform mixing of grain with protein, vitamin and mineral supplements.

The incidence of stomach ulcers sets the lower limit of particle size. Researchers in Kansas found that particle size smaller than 700 to 800 microns led to a 0 to 50 percent increase in the incidence of stomach ulcers in finishing pigs.

Very small particle size also increases problems with feed bridging in bins and feeders.

Factors that affect particle size

Many factors related to grain affect the particle size when grinding or rolling grain:

  • Kernel size
  • Moisture content
  • Fiber content

Mechanical factors also play a role in particle size:

  • Hammer speed
  • Hammer shape
  • Screen wear
  • Screen size
  • Roller speed

Develop and follow a maintenance schedule for hammermills and roller mills. Properly maintained and operated hammermills or roller mills can produce the desired particle size of 700 to 800 microns. Run periodic particle size analyses of feed to determine if your hammermills or roller mills are working properly.

Continuous flow mills

Continuous flow mills add ingredients based on volume. This process assumes that each ingredient has a constant bulk density. When the bulk density of ingredients changes, the mill still adds a given volume of material. That volume doesn’t contain the proper amount (pounds) of ingredient anymore. Thus you need to check the calibration of continuous flow mills for all diets at least once a month and every time you purchase a new batch of ingredients.

Consult the Pork Industry Handbook publication “Calibrating Meter-Type Feed Mills” for more details about this process.

Batch processing

With batch processing mixers, you add each ingredient individually. This system often consists of a portable grinder-mixer. For better accuracy, make sure you add these ingredients by weight, not volume. You can easily equip a portable grinder-mixer with a scale. Inaccurate ingredient amounts can affect pig performance and add to production cost. Thus over time, your cost savings pays for the scale.


Make a list of ingredient names and amounts you use in each swine diet. Check off each ingredient as you add it to the mixer. This will help you keep track of what you’ve added.

It’s hard to evenly mix ingredients added in small amounts (less than 1 to 2 percent of the diet) throughout a batch of feed. You should premix these ingredients with cereal grain and add in amounts of no less than 40 pounds per ton. A clean cement mixer works well for premixing.

The order that you add ingredients to the mixer will affect the time it takes to evenly mix the ingredients in the feed.

  1. Add at least one-half of the grain first.
  2. Add all premixed ingredients.
  3. Add all protein sources.
  4. Add the remaining grain.

A good rule of thumb is to mix the feed for 15 minutes from the time you added the last ingredient. It’s always best to follow the manufacturer’s recommendations on mixing time for the size and style of your mixer.

The feed ingredients won’t separate if their particle size is uniform. Make sure you don’t overfill mixers. Mixing efficiency declines when the mixers are too full.

Make sure you use every effort to guard against drug carryover from medicated to non-medicated feeds.

  • Drugs carryover because medicated feed particles cling to the inside of the mixer.
  • There may also be traces of medicated feed in discharge augers or the bottom of the mixer after unloading.

Mix medicated feeds first, followed by nonmedicated sow feed. This will flush out traces of medicated feed from the mixer.

Always mix non-medicated feeds last. If you can’t carry out proper sequencing, flush the mixer with ground corn and clean it thoroughly by hand.

  • Store feed in a clean, dry place to maintain quality.
  • Protect the feed from insects and rodents.
  • Empty bulk storage bins often so that no stale feed remains in the bin.
  • Clean the auger boot when the bins are empty. Often, wet, moldy feed builds up around the auger intake.
  • Don’t allow feed to sit in the feeders for extended periods of time. A pig’s feed intake may decline if stale feed is present.
  • Fill feeders often enough to provide the pigs fresh feed. Add enough feed for
    • One week to grow-finish feeders
    • One or two days to nursery pig feeders
    • One day to lactating sow feeders
  • Keep feeder holes free of wet, soiled feed and remove feed buildup in corners. These conditions lead to mold growth.

Testing your feed and feed ingredients

The key to a quality control program is periodic laboratory testing of ingredients and feed. These tests require you to take representative feed samples. If your samples aren’t representative, the test results won’t accurately reflect the nutrient content of your ingredients or feed.



Sample and test each new batch of grain because grains often vary in nutrient content. These test results can help you formulate diets.

You don’t need to sample soybean meal as often because processors are bound by law to meet guaranteed analysis on feed tags. It’s still a good idea to sample soybean meal sometimes. If the protein content doesn’t meet tag guarantees, you’re eligible for a rebate. Also check the soybean meal’s calcium content. Sometimes calcium is added to soybean meal to enhance flowability. This results in calcium levels higher than normally found in soybean meal.


If you purchase a premix from a reputable company, you don’t need to routinely send samples for testing. Lab tests for vitamins and trace minerals are costly.

Reputable companies pay close attention to the quality control aspects of manufacturing premixes. Nonetheless, it is a good idea to sample each shipment of premixes and keep samples stored in a freezer. If problems with the premix develop, a sample is available for lab analysis.

Final feed

You should always, at least, sample and test your final feed quarterly. Preferably, you should lab test your finished feed every two months. Testing your final feed often will help you determine the quality of feed your pigs are eating. Lab tests are the first step in troubleshooting feed manufacturing problems.

Feed suppliers often use synthetic amino acids, particularly lysine, so they can use less soybean meal in complete diets. In this case, crude protein content of the final diet may be less than you expect. Thus a more accurate way to check the nutritional value of a diet is by looking at lysine content instead of crude protein. Testing for lysine is more costly than crude protein.

Understanding lab test results can be confusing. Lab results aren’t carved in stone. Labs do make mistakes from time to time and there are normal differences in lab tests. Table 1 shows acceptable differences in lab tests.

If a lab test of your final feed shows a certain nutrient content is outside the normal range, you should test another sample. Don’t base major changes in feeding programs on the results from one feed sample.

If repeated tests show the nutrient content is outside the acceptable range, then there’s likely an error in formulation, mixing or sampling. You may need to consult a nutritionist to help troubleshoot your feed mixing process.

Example of acceptable differences in laboratory tests (adapted from Reese and Brumm)

Nutrient Variation Calculated level Normal range
Crude protein 3% 16% 15.5 to 16.5%
Lysine 5% 0.70% 0.66 to 0.74%
Calcium 5% 0.65% 0.62 to 0.68%
Phosphorus 5% 0.50% 0.47 to 0.52%
Trace minerals (zinc or iron) 5% 100 ppm 95 – 105 ppm

A few commercial labs are available for testing feed samples. Contact your county agent, state Extension specialist or feed dealer for names and addresses of commercial labs. Often, feed ingredient suppliers will offer lab services to their customers as well.

It’s best to call a laboratory before submitting a feed samples. This allows you to inquire about the following:

  • Cost
  • Sample size needed
  • Type of tests available
  • Turn-around time

Parsons, M. J., T. J. Gall and M. G. Hogberg. 1982. Analysis of Michigan corn and feed samples.Michigan State University swine research report no. 437, p. 63.

Shurson, G. C., T. Nye and D. B. Gerber. 1988. Summary of results from the 1986-87 Ohio feed analysis survey of gestation and lactation rations. Ohio swine research and industry report, p. 20.

Bache, D. H., T. Cline and K. Jackson. 1985. Economics of good feed mixing. Purdue University, West Lafayette, Ind.

Christensen, C. M., C. J. Mirocha and R. A. Meronuck. 1988. Molds and mycotoxins in feeds. University of Minnesota extension folder FO-3538.

Wu, J. F. 1984. Effects of particle size of corn, sorghum grain, and wheat on pig performance and nutrient digestibility. Ph.D. diss., Kansas State University, Manhattan, Kans.

Purkhiser, E. D. and P. D. Bloome. 1984. Calibrating meter-type feed mills. Pork industry handbook,factsheet 94.

Reese, D. E. and M. C. Brumm. 1988. Mixing quality swine feed. University of Nebraska Lincoln extension bulletin G88-892.

Lee J. Johnston, Extension animal scientist and Jerry Hawton, professor emeritus of swine nutrition and management, College of Food, Agriculture and Natural Resource Sciences.