Weather’s influence on grain quality

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What does it mean to the pig?

Aflatoxin Weather can have a significant impact on the grains used in swine diets, and hence, on the pigs consuming those grains, says Dr. Steve Ensley, veterinary toxicologist at the Iowa State Veterinary Diagnostic Laboratory. It’s more of an issue in some years than others, with last year’s drought in the Midwest providing a prime example.

According to Ensley, these effects include:

  • Production of fungi growth that produce mycotoxins
  • Decreased test weights of grains, where nutrients may be diminished
  • Decreased yields
  • Storage issues after grain is harvested
  • Substitution of one grain for another, based on the predicted weather during the growing season, and subsequent nutritional differences between the two

“Weather has a constant influence on grain during planting, growing, harvest and storage,” says Ensley. “A major factor of the weather’s influence on grain quality can be on how much of what crop will be planted on available acres.”

Producers are using a variety of grains and nutrients in swine diets as a result of high prices for corn and soybeans. “With potential decreasing availability of corn and soybeans, and reliance on alternative crops, this will have a direct influence on pig diets and the resulting feed efficiency and rate of gain,” Ensley notes. “Alternative grains to corn include sorghum, wheat, barley and bakery byproducts.”

Ensley explains that sorghum has a potential ergot alkaloid that corn does not, which can cause a potential problem. Also unlike corn, wheat and barley can contain ergotamine. Bakery products may have inconsistent concentrations of protein, fats and carbohydrates.

Other alternative sources include corn co-products, field peas, wheat midds and soybean hulls. “We see a lot of variability in these products,” he says. “As we change diets, we need to learn more about how it affects the animal.”

While a producer’s choice is dependent on feed costs and what feed grains are available, it’s important to make sure the pigs’ nutrient needs are being met, stresses Ensley.

“Molds may grow on grain during all phases of growth,” he points out. “Aspergillus grows best at high temperatures and produces aflatoxin; Fusarium fungi grow best in cool, wet weather, producing vomitoxin, fumonisins and zearalone. Molds also grow on small grains, and in addition to the other mycotoxins, we see Claviceps purpura that will produce ergotamine.

“As bacteria and fungi grow on feed, they produce heat, which can increase the growth of these organisms. The presence of these fungi does not mean mycotoxins will be produced, but the potential for their growth is there. Temperature, moisture and storage time can increase the production of molds.

Storage Concerns
Grain quality will not increase during storage, says Ensley. A best-case scenario is that the grain quality will be maintained.  “Grain moisture and temperature affect storage molds,” he says. “We’re still seeing some aflatoxin concentrations in stored grain that are higher than when the grain was harvested.”

Testing for aflatoxin can be difficult, continues Ensley. “Individual kernels can contain up to 400,000 parts per billion (ppb) aflatoxin; just one kernel at that level in five pounds or corn can cause the sample to be at a level of 52 ppb for aflatoxin. The sampling error for aflatoxin in corn coming out of the field is 25 to 40 percent. The more we sample, the more accurate we can be.

“People want to use the black light test – it’s fast, but it’s not very accurate,” he continues. “It’s better than not doing anything, but too many people are pressed into service to test, and they don’t do lab work year ‘round, so they’re not going to be as accurate.”

Ensley notes that more recently, an ELISA test has been used to identify aflatoxin. Although it’s not the ultimate answer, it is more science-based.

Table 1: Moisture Concentrations on a Percent-Wet Basis*

Storage Period Corn Soybeans
Sept.-Oct. 14 12
Nov.-March 15 13
April –May 
14 11
June-Aug. 13 11

* Reduce the moisture concentration by one percentage point when storing low-quality grain. To reduce the incidence of molds and insects, cool and dry the grain immediately after harvesting.


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