Some producers are so worried about mycotoxins that they immediately assume the worst when a little mould is found on their grain.
This reaction is not necessary because all moulds don’t produce toxins. As well, mycotoxicosis can occur even when feed isn’t visibly mouldy.
Fungi will grow only under specific conditions. Feed’s moisture content must be more than 14 percent, the temperature must be warm enough to support fungal growth, oxygen must be available, and relative humidity must be more than 70 percent.
There are many mycotoxins, each produced by certain fungi that prefer to grow on specific feeds. Aflatoxins are released by several fungal species that grow readily on grain and peanuts. As little as 0.2 parts per million of these toxins in feed will cause liver damage in calves.
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Aflatoxin levels over one ppm can cause severe organ damage and death in adult cattle. Because blood clotting can be disrupted, individuals are often seen with bloody diarrhea before they die.
Feed containing low levels of aflatoxins can decrease growth rates, lower feed efficiency, and increase the incidence of other diseases. Feed or liver samples can be tested for aflatoxin content.
Tricothecenes are produced by fungi that grow well on grain and some forages in cool, undulating temperatures.
Tricothecenes can cause shock and death within days of exposure if large quantities are eaten. At low doses, they cause vague signs like reduced feed intake and weight gains, diarrhea, and poor reproductive performance. These symptoms are so nonspecific that mycotoxins are not likely to be at the top of a diagnosis list.
Grassland staggers occur when cattle eat forages containing tremorgenic mycotoxins. Perennial ryegrass, even if dried, is linked to this toxicity.
Symptoms usually start within seven days of consuming contaminated feed. Cattle appear normal at rest, but when stimulated to move, they exhibit a characteristic stiff, spastic gait. Muscle spasms and seizures follow.
The seizures will diminish in frequency over a two week period following a diet change or a move to a different pasture.
Ergotism is a well recognized disease caused by the fungus claviceps that grows in grain seed heads. Though nervous signs such as ataxia and convulsions can occur, ergot poisoning is better known for its ability to cause dry gangrene of the feet and ears. This toxin causes blood vessels to spasm, which effectively cuts the blood supply to the extremities.
There are many other recognized mycotoxins and probably many yet to be isolated. For example, feeding mouldy hay has been implicated as a cause of gastrointestinal disturbances, liver disease and photosensitization.
Preventing mycotoxicoses is difficult. Researchers recently tried to determine which management practices affect mycotoxin production. They found that no specific practice will prevent the problem. Mould growth on feed can be reduced through management, but it can’t be eliminated completely.
The study also found that routinely testing feed for toxins has questionable value because the mycotoxins occur in highly concentrated pockets that can be easily missed with random sampling.
