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April 2004

Drop in on any dairy producer’s conversations about feed management and you’ll likely hear the term "mycotoxin" used. It may be a common enough term, but many dairy producers freely admit they don’t know much about mycotoxins , or how they affect dairy cows.

Part of the confusion about mycotoxins exists because of their elusive nature. Symptoms in dairy cattle are often wide-ranging and make diagnosis difficult. Multiple strains of mycotoxins can exist in the feed and distribution is usually not uniform. As well, there are inherent problems with sampling and analysis.

Mycotoxins are poisons that are produced by molds, a type of fungus. The molds that lead to the production of mycotoxins can be present in almost all dairy cattle feedstuffs, including grains and roughages. Growth can occur virtually anytime – in the field before harvest or post-harvest, during processing, storage or feeding.

Most frequently, mold growth and the accompanying mycotoxins occur because of extreme weather conditions (which cause plant stress), poor storage conditions or improper feeding practices.

Mold growth and mycotoxin formation are most likely when there is proper moisture; sufficient oxygen; a suitable temperature; physical damage to the feedstuff; and the presence of fungal spores.

Strains of three genera of fungi produce the mycotoxins of most concern to dairy cattle: Aspergillus, Fusarium, and Penicillium. The strain, aflatoxin, is produced by Aspergillus molds. Deoxynivalenol (DON), zearalenone, T-2 Toxin and fumonisin are produced by Fusarium molds. Ochratoxin is produced by Penicillium molds. These mycotoxins cause the most economic loss for dairy producers.

Diseases resulting from the consumption of mycotoxins are called mycotoxicoses. In dairy cattle, mycotoxicoses may be expressed through reduced milk production, poor performance among fresh cows and increased incidence of disease. There usually is intermittent diarrhea and, frequently, reduced or erratic feed intake.

Symptoms may be wide-ranging and not specific. They might include: reduced feed intake or feed refusal; unthriftiness; an undernourished appearance; rough hair coat; subnormal production; increased abortions or embryonic mortalities; silent heats or irregular estrus cycles; expression of estrus in pregnant cows; and decreased conception rates.

Mycotoxins are not infectious or contagious.

Through his nutrition consulting services, Rationale, Inc., James Huffard, III, Crockett, Va., says he frequently runs into issues with mycotoxins. He likens the effects of mycotoxins to a roller coaster. "The accumulation of toxins in the cow from the feed makes her sick, so she decreases consumption and production declines," he explains. "Then, as she starts feeling better (due to a decrease of toxin intake), she increases her feed intake and the ingestion of toxins. The cycle repeats itself – thus, the roller coaster effect."

Dave Endres, Lodi, Wis., first discovered his herd had problems with mycotoxins when he noticed inconsistent manure stools, depressed components in the milk and increased incidents of acidosis. "We had the feed checked and discovered small amounts of vomitoxin," he said.

Vomitoxin, or DON, is one of the most commonly detected mycotoxins and may be present in as much as 50-80% of all feeds. A positive analysis for DON suggests the presence of other, more problematic mycotoxins.

One of the most problematic, aflatoxin, is of major concern because it is carcinogenic and commonly found in corn. Aflatoxins are easily absorbed from the gastrointestinal tract, extensively metabolized and eliminated from the body in a relatively short time. Because of this, they pose a threat to humans and animals alike.

Crops or byproducts that are grown under heat-stressed conditions are more likely to have high aflatoxin levels.

Major efforts have been directed to eliminate aflatoxins in the food supply. The Food and Drug Administration (FDA) limits aflatoxin to no more than 20 parts per billion (ppb) in dairy cattle rations and .5 ppb in milk.

The notorious aflatoxin is particularly frustrating to dairy producers. Typically, herd health issues increase, but are not expressed as a single disease - rather a variety. There may be more mastitis, more milk fever, more ketosis, more displaced abomasums, more early embryonic deaths. Fresh cows may not peak. Cows have overall suppressed immunity.

Perhaps the highest cost of aflatoxins to the Registered Jersey breeder is reduced reproductive performance. This translates to increased days open, higher health care costs, reduced genetic gain and lower overall production.

If a dairy producer suspects a mycotoxin problem exists, the foodstuff should be immediately tested. Care should be taken when collecting samples, since it is notoriously difficult to obtain a representative sample.

To collect a representative sample:

1. Pull samples from multiple locations within a lot, mix well and label. Do not mix samples from different lots.

Typically, molds grow in "hot spots" in feed storage areas, so mycotoxin levels are not evenly distributed. Additionally, levels of molds are higher on the silo face and can quickly grow when exposed to oxygen.

2. Take samples from the total ration, as well as from individual ingredients.

3. Use a grain or forage sampling probe to obtain samples.

4. Collect at least 10 pounds of feedstuff and mix thoroughly

5. Send two to five pounds to the laboratory for analysis.

To prevent mycotoxins from increasing during transit to the laboratory, dry the sample at a moderate temperature, treat it with a mold inhibitor, or freeze it and ship overnight on ice.

When dealing with mycotoxins, an ounce of prevention is truly worth a pound of cure, since there are few ways to completely overcome problems once they are present.

"I’ve found that the best way to deal with mycotoxins is on the forage end, rather than on the cow end," said Endres.

Since the mycotoxins the Endres’ dealt with are predominantly soil-borne, they strive to exclude as much soil and ground-level forage as possible in the ration. They no longer use a rake in hay production, but now use a merger instead.

Endres also inoculates all silos with an inoculation to hasten the fermentation process. A silage inoculant improves the silage and reduces the potential for spoilage and mold growth later, when the silage is removed.

The best way to prevent mycotoxins is to control the environmental factors that influence mold growth. When harvesting grain, minimize damage to the seed coat and screen the product to reduce broken kernels.

Ammonia, propionic acid and microbial enzymatic additives have been shown to be partially effective in inhibiting mold growth in silage. To formulated feed, add .5 percent hydrated sodium calcium aluminosilicate. Ammoniation of grains can destroy some mycotoxins.

Store grains and other dry feed, such as hay, at moisture levels less than 14 percent. Store all feed at relative humidity levels under 70 percent. Keep oxygen availability less than .5 percent.

Seal bunker silos securely with plastic and place cut tires side by side over the entire covering. Quickly patch holes in plastic covers, silage bags and wrapped bales. Do not allow rain to penetrate the upper layers of spoiled silage.

Remove at least six inches of silage per day from the face of a bunker to keep ahead of spoilage. Use a silo facer to remove silage and leave a smooth surface, which is less susceptible to mold growth.

Remove leftover feed from the bunk every day. Clean storage systems regularly. Pay particular attention to animals when changes in the feeding regimen are made, such as opening a new feed bunker or switching feed suppliers.

Be especially watchful for mycotoxin-related issues when purchasing feed that was harvested following a drought. Take care when purchasing whole cottonseed from a broker or gin. Reputable feed companies can provide commodities or feed products that have been tested and are free of or have low levels of toxins.

If the only feed available is contaminated with mycotoxins, and it is not possible to completely replace it in the diet, dilute the proportion by mixing with "clean" feed. Include adsorbents, such as bentonite or aluminum silicates, in the ration to bind the mycotoxins and prevent absorption. Or, feed microbials that have been developed to alter the structure of mycotoxins, render them non-toxic or destroy them altogether.

While every dairy herd may be threatened by mycotoxins, it can be protected through prevention. Arm yourself with information, perform sound feed management practices and you’ll reduce your dairy herd’s risk for mycotoxicosis.

For more information on mycotoxins, consult the following websites: moormans.com/dairy/DairyFF/dairydec96/mycotoxi.htm; aces.edu/department/grain/ANR767.htm; ansci.cornell.edu/plants/toxicagents/mycotoxin.htm; and edis.ifas.ufl.edu/BODY_DS152.