The abundant corn crop of 2004 carries with it a very real threat of mycotoxins.
Since feed accounts for 65-70% of the total cost of raising hogs, and corn makes up approximately 80% of swine diets in the U.S., any changes in corn quality can potentially have a very large impact on pig performance and producer profitability.
A closer look at the 2004 U.S. corn crop leaves us with a “good news — bad news” scenario. The good news: It was the largest on record (11.7 billion bu., or 16% higher than last year's previous record of 10.1 billion bu.), according to the November 2004 USDA Corn Crop Report.
Current corn prices reflect those record yields. The current corn price in South Dakota is $1.61/bu., roughly half the price we saw last spring, which means a tremendous savings to pork producers.
The bad news, however, is the U.S. experienced one of the coolest growing seasons ever. That left us with some concerns about corn quality — most notably the presence of mycotoxins and variations in nutrient content.
Finding, Feeding Corn With Mycotoxins
Mycotoxins are toxins produced by molds on or in grains. They can have a significant impact on pig growth and reproductive performance.
The main mycotoxins pork producers are concerned with are aflatoxin, fumonisin, vomitoxin and zearalenone.
Aflatoxins, which suppress immune function and performance, are produced in humid, warm conditions, and are mainly a concern to producers in the southern states. However, there have been reports of aflatoxins in Illinois and Indiana.
Zearalenone (reproductive problems), vomitoxin (feed refusal), and fumonisin (pulmonary edema) typically occur in the cool, damp conditions experienced in most of the Corn Belt this year.
Another exacerbating factor caused by last year's record crop was a shortage of storage space. Consequently, much of the corn was harvested at a higher moisture content and then stored in piles on the ground. Rain and snow have added more moisture to the piled corn — setting it up for future mycotoxin production.
Any producer concerned about a potential mycotoxin problem should send a representative corn sample to a diagnostic lab for mycotoxin screening. Test kits are also commercially available for producers to test for mycotoxins.
A quick, on-farm test would be to isolate a few pre-pubertal gilts and feed them the suspected grain. If zearalenone is present, the vulvas will become red and swollen. If vomitoxin is present, the gilts will eat a few mouthfuls, possibly vomit, and then completely back off feed. Black lights are not recommended for detecting mycotoxins, since they only illuminate the molds, not the mycotoxins.
What should a producer do with a bin full of mycotoxin-contaminated grains?
The best option is to feed it to beef cattle, since they have a much higher tolerance to mycotoxins. The second best alternative is to blend it with “clean” corn and feed it to grow-finish hogs only.
Table 1 shows the maximum recommended concentrations of common mycotoxins for the complete diet. Due to the severe effects mycotoxins have on sows and nursery pigs, it is strongly recommended to keep them out of feed for those phases.
There are commercially available additives that claim to work against mycotoxins. Some work well against aflatoxin, as do pellet binders like sodium bentonite. However, these additives are generally considered ineffective against all other mycotoxins.
The best advice is to prevent the molds from occurring in the first place, and if they do occur and produce mycotoxins, to limit their use in swine diets.
Mycotoxin Predictor Available
For 2005, there is a tool available to help grain producers predict the mycotoxin concentration in their corn crop. Patrick Dowd, an entomologist at the Agricultural Research Service National Center for Agricultural Utilization Research in Peoria, IL, developed Mycotoxin Predictor 1.1, a software program copyrighted by collaborators at Illinois Central College.
The Windows-friendly program uses equations to mathematically predict mycotoxin levels using temperature, soil type, numbers of insects and other factors that influence the molds' growth and spread. With this information, a crop farmer can predict the likelihood and levels of mycotoxin contamination more than a month before harvest.
Mold growth is often tied to insect damage. So if the program predicts that mycotoxin problems are likely to arise from heavy insect feeding, the farmer may opt to spray the crop before caterpillars can hide inside corn husks and cause the damage that allows mold growth.
Nutrient Content Concerns
Another concern with the 2004 corn crop is variation in nutrient content levels, which can significantly change the nutrient composition of the diet.
Weather conditions, corn variety, yields and other factors have caused nutrient content to vary greatly. Research from the Southeast South Dakota Research Farm in 2003 showed that the protein level in 208 corn samples ranged from 5.5% to 11.8% crude protein. And in a trial published in 1999 by the National Research Council committee on swine nutrition, corn samples from 15 different states ranged from 9.06% (North Dakota) to 7.31% (Ohio).
Lysine concentrations from these same samples varied less than crude protein did, ranging from 0.25% to 0.30%.
Researchers also found that crude protein and lysine in corn were positively related. They observed that the lysine content of corn increased 0.018% for each 1% increase in protein content.
This information can be used to determine how much corn's dietary lysine content will be influenced by variations in crude protein content.
For example, if we use three samples of corn with protein levels of 5.5%, 8.3% and 11.8%, that would correspond to lysine levels of 0.21%, 0.26% and 0.32%, respectively (Table 2). Assuming we want to feed a 120-lb., high-lean genotype gilt, we need a diet containing 1.01% total lysine. The control diet using “normal” corn (8.3% protein) would contain 1.01% lysine. However, if we use the low- and high-protein corn at the same inclusion rate, the complete diets would contain 0.97% lysine and 1.05% lysine, respectively, a .04% point change from normal corn.
What do these differences mean to the pig?
If a gilt eats 4.5 lb. of feed daily, it is getting 20.4 g. of lysine/day from the normal corn, 21.5 g. from the high-protein corn and 19.8 g. from the low-protein corn. If pigs on the low-protein corn eat just an extra 0.1 lb. of feed/day, they will meet their daily lysine requirement of 20.4 g./day.
To adjust corn and soybean meal (SBM) levels to get to the 1.01% lysine diet, you would need to decrease the low-protein corn from 1,415 lb./ton to 1,388 lb./ton, and increase the soybean meal from 543 to 570 lb./ton of complete feed. Using corn at $1.61/bu. and soybean meal (46.5%) at $160/ton, that's an increase in diet cost of $1.39/ton of feed.
Impact on Pig Performance
Will these differences affect pig performance?
It depends on how much the animals are eating each day and how close the animals' actual nutrient requirements are to being met. With high-feed-intake pigs and/or higher dietary nutrients levels than required, protein variability in corn won't affect pig performance very much. If you are right on the animals' requirements, or feed intake is reduced, you may want to adjust your diets accordingly.
Remember that in this example we used a very wide protein range for corn. In general, if your corn is consistently closer to the average corn levels, don't adjust your diets. If your corn is consistently high or low, then you can make slight adjustments.
The past year has been a roller coaster ride for pork producers — from low hog prices with high feed costs, to high pig prices and low feed costs. The 2004 corn crop has significantly reduced feed prices. Nutrient variability, unless at the extremes, really won't impact pig performance. However, mycotoxins are a real threat and pork producers need to manage to prevent any problems they could cause.
|Pig||Vomitoxin, ppm||Zearalenone, ppm||Aflatoxin, ppb|
|*Pork Industry Handbook fact sheet #129 — Mycotoxins and Swine Performance. These values are for the complete diet, not just concentrations in the grain.|
|Crude Protein||Lysine||Corn||Soybean Meal||%Crude Protein||%Lysine||Costa||g. lysine per dayc||Feed to get 20.4 g. lysine||Difference from Control Diet|
|Constant amount of corn & soybean mealb|
|Constant amount of lysine|
|aCorn @ $1.61/bu. bSoybean meal (46.5% @ $160/ton). c4.5 lb. of feed consumed/day|