Feeding corn contaminated with mould or mycotoxin to swine

Overview

Mycotoxins are toxic compounds produced by moulds or fungi that can contaminate crops. Ontario’s warm, humid growing season creates ideal conditions for fungal growth, making mycotoxin contamination a recurring concern for farmers.

Mycotoxins in corn can pose significant risks to animal health, feed efficiency and the overall productivity of swine operations. In Ontario, the most common mycotoxins in corn are:

• deoxynivalenol (DON), also called vomitoxin
• zearalenone
• fumonisin
• aflatoxin

It is recommended to test for mycotoxins in corn, corn silage or corn-based feeds, especially after drought or flooding damage.

Effects of feeding mycotoxin-contaminated corn

Swine are highly sensitive to mycotoxins. These toxins can reduce feed intake, slow growth, harm reproduction and increase vulnerability to disease. The impacts vary by type of mycotoxin.

Deoxynivalenol (DON), ppm

• decreased feed intake and average daily gain
• vomiting or feed refusal when concentration is high
• diarrhea
• immune suppression (increased vulnerability to disease)

Zearalenone, ppm

• estrogenic effect leading to poor conception rate, infertility and other reproduction challenges
• vulva swelling
• decreased sperm production and libido
• vaginal and rectal prolapse

Fumonisin, ppm

• immune suppression
• pulmonary edema
• liver damage

Aflatoxin, ppb

• decreased feed intake and average daily gain
• abortion
• liver damage
• immune suppression

Source: Kansas Swine Nutrition Guide.

Concentrations of mycotoxins should be adjusted downward if feed intake is reduced, or other signs of toxicity are seen.

Considerations and corrective steps

The amount of corn fed depends on:

• class of pig — pigs may consume corn at levels up to 100% of the grain portion of a ration
• cost and availability
• mycotoxin levels — these ultimately determine the acceptable amount of corn in a ration

Initial corrective steps for mycotoxin-contaminated corn include:

• cleaning mouldy grains and removing fines and lightweight grains suspected of mycotoxin contamination
• mixing contaminated corn with mould-free corn or other types of clean grains

After feeding mycotoxin-contaminated corn, monitor animals closely:

• reducing the amount of the suspected corn in the feed by 50% if moderate effects are seen
• stopping use of the corn for at least a week if effects are severe
• sampling the corn and retesting to determine a safe feeding level if animals improve

Test corn or corn-based feeds for mycotoxins, especially after drought or flooding damage.

Get more information on sampling feed to test for mycotoxins.

Once you receive test results, check whether they are provided on an as-is basis or a dry matter basis. Results are often given as-fed, so you may need to convert them to a dry matter basis to calculate the mycotoxin concentration.

Example conversion from as-fed to dry matter basis:

Corn with 15% moisture analyzed at 5 ppm DON as-fed:

• 100 - 15 = 85% dry matter
• 5 ÷ 0.85 = 5.9 ppm DON on a dry matter basis

Results may also use different units. For example:

• ppm = mg/kg = μg/g = 1,000 ppb
  • add alternative cereal grains to help reduce the toxin concentration
  • increase the nutrient density of the ration to compensate for reduced intake
  • boost the levels of vitamins, minerals, and amino acids by 5 to 20%, depending on the severity of feed refusal
  • add an appropriate mould inhibitor (such as sodium or calcium propionate or organic acids) to the stored grain to prevent further mould

Find mycotoxin survey results up to 2025 at Field Crop News: Ontario Grain Corn Ear Mould and Deoxynivalenol (DON) Mycotoxin Survey.

You can calculate the maximum percentage of contaminated corn that can be safely included in the total ration dry matter using this formula:

% maximum inclusion rate = (safe level in TRDM ÷ concentration in corn DM) x 100 

Example:

For lactating sows, the maximum safe level of DON is 1 ppm. If the corn analysis shows 5 ppm of DON on a dry matter basis, the maximum inclusion level in the total ration dry matter (TRDM) can be calculated as:

(1 ÷ 5) x 100 = 20%

This means that the corn can make up a maximum of 20% of the total ration dry matter based on the DON level.

Apply the same calculation for other mycotoxins. Poor palatability of mouldy corn may lower feed intake and determine inclusion rates. When in doubt, choose the safer option and monitor animals.

Next steps

If you suspect a mild contamination:

• add alternative cereal grains to help reduce the toxin concentration
  • increase the nutrient density of the ration to compensate for reduced intake
  • boost the levels of vitamins, minerals, and amino acids by 5 to 20%, depending on the severity of feed refusal
  • add an appropriate mould inhibitor (such as sodium or calcium propionate or organic acids) to the stored grain to prevent further mould