Advice for Using Weather-Stressed Corn in Swine Diets – Part One

( National Pork Board and the Pork Checkoff )

In much of the U.S. corn is the largest component in swine diets, but adverse weather conditions affect corn quality. This is because of late planting, a cool growing season, drought and/or early frost. This stressed corn is docked at the elevator, leaving the corn producer the option to market the corn through the elevator at a reduced price or through livestock in an attempt to add value to it, according to an article from the South Dakota State University Extension (SDSU Extension). This corn can be used in feed, as long as it’s nutritional value, potential for mycotoxin contamination and how changes in bulk density affect feed mixing and transportation are understood. 

Differences in nutrient composition 

Weather-stressed corn is typically lighter than the normal 56 lbs/bushel of #1 yellow corn because the kernel hasn’t fully matured, note the article authors, Bob Thaler and Ryan Samuel, SDSU Extension swine specialists. Light-weight corn (LWC) is higher in protein, fiber and ash than 56 lb corn, but is lower in starch and fat, which results in a lower energy content.

Because protein is one of the more costly components of a swine diet, one might be tempted to assume that the higher protein content in LWC also means it has a higher lysine content, which would decrease the need for soybean meal or synthetic amino acids to meet pigs’ lysine requirement. But research has shown that the % lysine in LWC increases at a slower rate than the increase in % protein.1 Therefore, producers should continue to use the same % lysine content for corn in the diet formulation, regardless of whether they are using 56 lb corn or LWC, to prevent amino acid deficiency that can lead to poorer performance. 

If it’s decided to feed LWC, there can be a decrease in the metabolizable energy content in the final diets since both the starch and fat concentrations in LWC are reduced, but this decrease depends on how light the corn is. The lighter the corn, the article states, the greater the chance lower energy concentrations and that will lead to poorer feed efficiency. Producers can add fat or oil to increase dietary energy level, but it is infrequently economical to do so. Options are to blend LWC with 56 lb corn (if available) or to only include LWC and get a reduction in feed efficiency. 

It is interesting to note, that multiple research stations in South Dakota have shown that corn test weight can be reduced down to 10% (50% corn) without affecting feed efficiency and that corn test weight can be reduced down to 25% (42 lb corn) before daily gain is affected. 

Feeding guidelines 

If there are no mycotoxins in the damaged corn, it can be used in late grower, finishing and gestation diets, however, depending on how light the corn is, daily feeding level may need to be increased in gestation to compensate for the lower energy value of LWC. Because energy intake needs to be maximized in nursery, early grower and lactation diets, it is not recommended to use LWC in these diets if possible. 

Often the price dock at the elevator is larger than the reduced feeding value of the corn so producers can potentially make money feeding LWC if the purchase price is low enough. The formula below from the National Swine Nutrition Guide can help determine whether or not the poor feed efficiency from feeding LWC is offset by the lower diet cost.2

(New diet cost – old diet cost / old diet cost) X 100 = maximum % reduction in feed efficiency allowable to use weather stressed grains. 

If this value is greater than the % reduction in feed efficiency, then the producer can make money feeding the LWC. But, if the % change in diet cost is less than the % change in feed efficiency, then the feed should not be used. 

For example, if using LWC will reduce total diet cost from $220/ton to $196/ton, that’s an 11% reduction in feed cost, so if the pig is only 6% less efficient, it is economically advantageous for the producer to use LWC, the article illustrates. 

(196-220 / 220) X 100 = -11% maximum allowable reduction in feed efficiency. 

On the other hand, if the reduction in feed efficiency was greater than the 11% maximum according to the calculation, then the producer would lose money feeding the LWC in pig diets. 

This equation and feeding recommendation are only valid if the LWC is free of mycotoxins. If the LWC is

In part two of this overview, mycotoxins and bulk density of LWC will be reviewed.

1. Johnston, L. 1995. Use of low-test-weight corn in swine diets and the lysine/protein relationship in corn. Swine Health and Production vol 3(4):161. 

2. Thaler, R.C. and D.E. Reese. 2010. Utilization of weather-stressed feedstuffs in swine diets. Chapter 24 - National Swine Nutrition Guide, D. Meisinger, Editor. 2010. US Pork Center of Excellence.


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