Mycotoxins in Feed

Mycotoxins in Feed

By Heather Smith Thomas

Mycotoxins in cattle feed are toxic fungal metabolites (such as Aflatoxin, DON/Vomitoxin, Zearalenone) that can occur in moldy, poorly stored, or drought-stressed crops, particularly corn, silage, and grains. Most commonly, mycotoxins are produced by species of Aspergillus, Fusarium, and Penicillium. The presence of mold does not mean the toxin is present, but it does mean that conditions are favorable for mycotoxin production.

These fungal metabolites are small organic compounds, intermediate products, or end products created during metabolism—the chemical processes in the body that break down food, drugs, or body tissues to produce energy and materials for growth, function, and repair.

Toxic fungal metabolites like mycotoxins can cause significant health issues in the animal that consumes them–like reduced feed intake, infertility, lowered milk production, and immune suppression. Preventing these negative impacts relies on proper harvesting, storage, and using adsorbents to make these mycotoxins less harmful.

Mycotoxins have always been a problem for cattle, but due to modern agronomic practices, feeding practices and feed storage there is greater mycotoxin prevalence today than in the past. Stockmen now have to deal with this issue more frequently.

Stephanie Ward, Dairy Science Extension Specialist and Associate Professor (North Carolina State University) says the dangerous fungi often grow on commodities commonly used as feedstuffs in the dairy industry. Molds like Fusarium can be produced both before and after harvesting, while Aspergillus and Penicillium mainly occur after harvest. The absence of mold on visual observation is not a guarantee that mycotoxins are not present, since the mycotoxins may remain even after the mold dies.

“Mycotoxins produced before the crop is harvested may remain stable during feed preservation, but some species may also grow on commodities during storage. Stress to the crop makes the feedstuff more susceptible to mold growth,” ways Ward. Stress for various feed products may be caused by drought, excess moisture, high temperatures, humidity, insect damage or some other problem.

Mycotoxicosis can affect cattle in several ways including increased incidence of Squamous Cell Carcinoma (including cancer eye), decreased appetite or complete feed refusal, impaired lactation and reproductive performance, rough hair coat, lameness and/or diarrhea. These signs may differ with the age of the cattle, stage of production, environment, interaction with other mycotoxins or diseases, stress, and the dose or length of exposure to the various mycotoxins.

Since mycotoxins often affect immune and organ function, any of these signs may indicate a much larger concern, but diagnosing mycotoxicosis is difficult. “Mycotoxins also affect different species of livestock differently. For example, vomitoxin (DON) may result in reduced intake in dairy cattle, but beef cattle and sheep seem more resistant to its effects,” says Ward.

Deoxynivalenol (DON), commonly known as vomitoxin, is a Fusarium-produced mycotoxin that contaminates wheat and corn, particularly in cool, wet conditions. It acts as a protein synthesis inhibitor, causing vomiting, abdominal pain, and diarrhea in humans, and severe feed refusal, reduced weight gain, and vomiting in livestock.

“Often, the only form of ‘treatment’ is removal of contaminated feed,” says Ward. When clinical signs occur, mycotoxin contamination should always be considered as a potential cause.

“Effects of mycotoxins may be more severe in a naturally-occurring setting compared to a controlled research setting. When mycotoxicosis is caused by naturally–occurring mycotoxins, multiple mycotoxins may be present causing interactions that increase the severity,” she says. Ruminants are a little more resistant to mycotoxicosis than some other species like pigs, but they are still susceptible. Dairy cattle seen to be more susceptible than beef cattle, particularly during early lactation when their immune system is already suppressed.

Pigs and young poultry are highly susceptible to mycotoxicosis, often showing severe growth retardation, immune suppression, and reproductive failure from contaminated feed. Other highly sensitive animals include dogs, horses, and young calves, while ruminants are generally more resistant but still vulnerable to high doses.

Ingesting small amounts of mycotoxins over time can cause mycotoxicosis, as can sudden ingestion of large concentrations. Thusit is important to consistently sample and test feed for mycotoxins, even though obtaining a representative and accurate feed sample is difficult. “Mold, and thus mycotoxin production, may occur in ‘hot spots’, and is not uniformly distributed throughout the silo or grain bin,” says Ward. This can cause inaccurate reports statingthat the feed is not contaminated.

She provides some tips for taking good samples for analysis. “Take core samples in multiple locations throughout the stored feed rather than taking a single grab sample. Preserve the sample by freezing or drying prior to shipment to the laboratory. This will prevent mold from growing and producing mycotoxins after the sample is collected.”

Always remember that a sample may be inaccurate. “If feed is reported to be negative for mycotoxin but clinical symptoms are still present, do not rule out mycotoxin contamination,” she says.

If you discover mycotoxin contamination in your feed, there are some things you can try. “Mycotoxin binders have been evaluated for years, but many of these are not available in the U.S. and there is limited information on the dosage needed. Clay binders include bentonites, zeolites, or hydrated sodium calcium aluminosilicate (HSCAS) clays. While most clays appear to be effective, research varies on how well they work. This may be due to the variety of mycotoxin and clay used in each study,” says Ward.

Some binders may be effective for numerous mycotoxins, but some are only effective for a specific toxin. “For example, HSCAS is known to be sensitive to aflatoxin, but not other mycotoxins. Additionally, some mycotoxins (such as zearalenone and ergot alkaloids) do not bind to these clays so the only real treatment is removal of the contaminated feed. If contamination occurs, diluting with uncontaminated feedstuffs is also an option unless the mycotoxin is above FDA action limits,” she says.

Dr. Larry Roth (Vice-President of Nutrition, Agrarian Solutions) does research on mycotoxins and works with nutritionists and veterinarians, beef and dairy producers to protect livestock from mycotoxins. “Mycotoxins are produced by molds as part of their survival mechanism—in what we call competitive exclusion. Molds couldn’t care less about their effects on us or our livestock; they just don’t want other things growing in their territory, so they create poisons. Our animals are collateral damage,” he explains.

Molds are opportunistic and readily start growing on plants that can’t fight them off. “Anything that stresses the plant, such as too much water, too little water, too hot or too cold can tip the balance and weaken the plant—making it more susceptible to things like mold. Then if the mold gets stressed by some of those same conditions, it puts out these poisons to keep other opportunistic organisms from growing in its home.”

Many modern agronomic practices favor molds. For example, crops today have greater canopy density than usually seen in nature. “There is much more canopy, and it holds more moisture. It also keeps out sunlight which is the best disinfectant, and hinders air movement, so these molds readily take off and grow,” says Roth.

It’s a good farming practice to leave crop residue on the soil surface but it may actually increase risk for mycotoxins. Farmers do minimum till and no-till to increase organic matter in the soil. “As soon as the new green leaves emerge, coming up through that old residue, they become infected with molds, and if the molds get stressed, they create their toxins,” he explains.

If farmers don’t pack silage as well as it should be, or don’t quickly cover it with oxygen-limiting plastic, the feed is subjected to weathering, poor fermentation and an increase in molds and mycotoxins. “We also utilize more feeds today that might contain mycotoxins. We feed a lot of by-products like distillers grains and corn gluten feeds that concentrate and raise the level of mycotoxins compared to what was in the base feed.” We also store feeds for later use, and sometimes inadequate storage conditions lead to mold formation due to poor harvest conditions or weather damage during storage.

“It seems like we have more of these molds and mycotoxin issues than we had in the past, and our animals today are also more susceptible. They are like fine-tuned machines compared to the livestock we had in the past.” We have selected cattle genetically for faster growth, more milk production, etc. and in doing so they have lost the genetic diversity they once had, which helped give them a stronger immune system.

“The analogy I give is the way we’ve fine-tuned vehicles for speed. We could take an old ranch pickup to the Indy 500 Speedway and drive along 10 miles an hour. Someone could throw a brick out there and that old truck would roll right over it and keep going. By contrast, if we take an Indy 500 car and whiz along at 180 miles an hour and hit that same brick, we will wreck and hit the wall. Our animals are like fine-tuned machines, and when little things come along, like mycotoxins, they can cause a wreck. It’s normal for a cow to have a calf, or wean a calf, but added stress like transport, or even vaccination and working those animals can make them more susceptible to the effects of mycotoxins,” says Roth.

“Two hundred years ago, a brood cow was eating dry grass and wasn’t fed corn silage or distillers grains. Today our animals are exposed to higher levels of mycotoxins, compared to what they would have eaten in the past,” he explains. The brood cow in her last trimester today might be fed corn silage or small grain silages or a little distillers because her nutrient requirements are greater as the fetus is growing fastest before calving, and after she calves and is producing milk.

“We are putting more mycotoxins into that cow, which lowers her immune defenses. Her immune system defends her against invading agents. If the immune system is hammered by mycotoxins, this is a nutrient drain. The cow only has a certain amount of nutrient resources to allocate. Now some of those nutrients she’d be putting into that fast-growing fetus and colostrum quantity and quality are diverted into defending herself. Her first priority is to survive,” says Roth.

If on top of that nutrient drain she goes through a bad winter, the cold wet conditions add more stress. If all these impacts comes together, the calves also suffer. “Cattle do not receive antibodies before birth (like a human baby does) and are dependent on colostrum for early protection. If mama has been exposed to mycotoxins, colostrum quantity and quality isn’t what it ought to be.” Milk production will also be impaired since some of her nutrients are being allocated to fight the mycotoxins.

“We must remember that mycotoxins are absorbed by the cow and can be stored in her fat when she is supposed to be gaining weight. Once she calves and is producing milk, she starts to metabolize some of that body fat.” That’s a normal situation to provide the necessary extra energy to produce milk.

“As she metabolizes body fat, however, the mycotoxins stored there are now free to float through the body. The liver is the body’s biochemical factory as well as a filter; everything must go through the liver, so it is working hard to detoxify these mycotoxins. It is normally busy making glucose and other nutrients the cow needs, but is now damaged and impaired in that capacity, because it is going through all the necessary detoxifying of mycotoxins,” Roth explains.

The same principles apply to dairy replacement heifers. “If they have to deal with mycotoxins in feeds, they won’t grow as well as we’d hoped. When we try to do a timed AI on heifers, we won’t have the success we hoped for. Those heifers probably are not as big as they ought to be, and won’t be as fertile, even though we go through all the timed AI steps,” he says.

“Then the first 20 days or so after breeding, the ones that did get pregnant (cows or heifers) need a lot of glucose to donate carbons to the rapidly-developing embryo. The glucose in this instance is not so much for energy; the embryo needs glucose as a source of carbon because it is growing so fast. Again, if the mycotoxins have changed the way the replacement heifer or the cow has allocated her nutrients, the first thing that suffers is her ability to get pregnant for the next calf. The body’s highest priority is staying alive, not reproduction.” That female must be healthy, with adequate nutrition.

“The cow’s priority after calving is producing milk,” he says. “Mycotoxins reduce the nutrients available for productive purposes—whether it’s the calf inside the pregnant cow, or colostrum for the calf at birth, or producing milk–and mycotoxins also reduce the reproductive success of a heifer,” says Roth.

Nutrients are expensive, so these mycotoxins are stealing profits. “I think of them as silent profit robbers. There are ways to head off these pick-pocket thieves and stop the mycotoxins. What we’ve done in the past is use clay, like bentonite. These binders will bind to aflatoxin but are ineffective against most other mycotoxins. Traditional mycotoxin binders can also reduce nutrient availability to the animal,” says Roth.

“The clay products tie up the amino acids that the animal needs for growth, milk production and the immune system. They also tie up vitamins A and E, which are crucial for immune function and reproduction,” he explains.

Other products utilize yeast cell walls. “They are like the clays; they are not that good at tying up the mycotoxins but are fairly good at reducing nutrient availability. So here at Agrarian, we’ve taken a different approach. We work with a beneficial bacterium that has been shown to trigger the animal’s natural defense mechanism against mycotoxins so the body can fight better. The animals have been exposed to mycotoxins forever and have developed their own way to kick mycotoxins out of the intestinal cells where they would otherwise be absorbed,” says Roth.

“These specialized bacteria trigger proteins that clean up the intestinal cells. They are like garbage trucks to haul the contaminants away. We simply need to trigger the natural defense and take it to the next level, to keep up with what’s been happening—greater prevalence of mycotoxins and cattle that are expected to function at a higher level, and traditional binders that are not very effective,” he says. “So now we are bringing in special probiotics that trigger the natural defense mechanism. The specialized bacteria in DTX (from Agrarian Solutions) are a research-proven and time-tested (over 25 years) method of protecting cattle against mycotoxins,” says Roth.

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