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What is the danger of Mycotoxin in swine diets?

Mycotoxins are produced by certain types of molds. If these molds invade feed ingredients, they may produce toxic compounds that contaminate feed. Molds can infect grain standing in the field as well as during harvesting, handling, and storage.

Although over 200 mycotoxins have been identified, only a few are believed to influence swine performance. Risk from mycotoxin-contaminated feeds depends on the age and health of the pig and level of toxin in the feed. The most severe effect is death, but low levels of mycotoxin can depress pig performance and general well-being. When pigs consume diets containing a harmful mycotoxin, the toxin can affect the pigs nervous system, liver, kidney, immune system, or reproductive process.

Aflatoxin, zearalenone, and tricothecene (vomitoxin and T-2 toxin) are the most frequently reported mycotoxin in feed. There is more information available about aflatoxin and its effect on pig performance than any other toxin. Each toxin is produced by a different mold. The conditions that promote growth of molds vary, although high moisture and warm temperatures are the primary requirements for mold growth on feedstuffs.

Aflatoxin

Aflatoxin is produced by Aspergillus flavus, which can germinate at lower moisture levels of 15 to 17 percent, but infection and growth require higher moisture. Aflatoxin production appears to be higher at grain moisture levels of 22 to 26 percent and temperatures of 80 to 90Á F. Conditions for aflatoxin production are ideal when temperatures remain high both day and night, although growth slows dramatically at temperatures above 95Á F.

The effect on pig performance, of feeding aflatoxin-contaminated grain, depends on the age and health of the pigs as well as the concentration of the toxin in the feed. Young swine are most sensitive to its effects. Symptoms occur with concentrations in the parts per billion (ppb) range. Small amounts can reduce pig performance and overall health. Aflatoxin at low levels (20 to 200 ppb) suppress the immune system and make pigs more susceptible to bacterial, viral, or parasitic diseases. Prolonged exposure may cause cancer, liver damage, jaundice, and internal bleeding. Over time, profits are reduced due to loss in efficiency, slower growth, and increased medical costs. High concentrations of aflatoxin (1,000 to 5,000 ppb) result in acute effects, including death.

Aflatoxin M1, a metabolite of aflatoxin, has been found in the milk of sows fed diets containing aflatoxin. Pigs nursing sows consuming feed with 500 to 750 ppb of aflatoxin had increased mortality and slower growth. Pigs were permanently stunted and performance was reduced to market weight even though they were not exposed to aflatoxin after weaning.

Preventing Mycotoxin

Mycotoxin usually appear in feed because one of the individual feed ingredients has been contaminated. Grain contamination may occur in the field. Drought stressed corn is less resistant to fungi and should be considered to be of high risk. To avoid mold problems, minimize stress with variety selection, planting density, irrigation, weed and insect control and adequate fertilization.

The two major environmental factors associated with fungal growth are temperature and humidity. Anytime humidity exceeds 62 percent, temperature exceeds 80Á F, and grain moisture levels exceed 14 to 15 percent, there is a greater chance that fungi will grow. The exception is zearalenone, which is produced under cool temperatures (less than 70Á F) and moist conditions.

Damaged feedstuffs are readily available food sources for mold growth. Anytime the kernel is cracked and the endosperm is exposed, there is high probability of mold growth. During harvest, adjust equipment to minimize kernel damage and to remove foreign matter. Ground feed is an ideal source of food for fungal growth.

During periods of high humidity and heat, ground feedstuffs and/or swine diets should not be stored over 10-14 days. Corn screenings are excellent media for fungal growth and have been associated with Fumonisin toxicity.

The time between harvest and drying is critical. That's when temperature and moisture conditions are often ideal for mold growth and toxin production. Consequently, do not delay drying grain for more than 6 hours and dry grain to recommended moisture levels.

Storage conditions are also important. Grain storage bins should be clean and in good repair. After drying, cool the grain to air temperature before loading the storage bin since hot grain can cause condensation, which sets the stage for mold growth and toxin production. Feed and grain storage bins should be cleaned at frequent intervals to prevent bridging of feedstuffs and formation of hot spots. Consider treating the grain (after drying and before storing) with an insecticide to reduce insect damage.

Fungal inhibitors, such as propionic acid, may be effective in preventing fungal growth on stored grains. However, fungal inhibitors have no effect on mycotoxin already present in the corn at the time of application. They only prevent future growth of fungi.

Regardless of all other factors, the critical point for controlling fungal growth in storage is grain moisture levels. Grain that is dry when placed in storage and kept dry (less than 14 percent moisture) will be unlikely to support growth of fungi that produce mycotoxins.

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