DON in Corn - What Does it Mean for Feeding Cattle?

This article was previously published in Ontario Beef, December 2018

Parts of the province, particularly south western Ontario, are seeing above average levels of DON in corn this year. This has left livestock producers raising questions about the risks of mycotoxins and safe levels for feeding livestock.

What is DON?

Deoxynivalenol, commonly known as DON or vomitoxin, is a type of mycotoxin, which is a compound produced by mould. While moulds themselves can reduce the quality of feedstuffs and can affect palatability, intake, and performance, mycotoxins have toxic effects on the body and at high levels in feed can impair growth, lactation, and reproductive performance in livestock. Although hundreds of mycotoxins have been identified, the physiological impact of only a handful is known. Mycotoxins are only produced by certain mould species and under specific environmental conditions. Although the presence of moulds is a good indication that mycotoxins may be present, laboratory test results may not always reveal a high level of mycotoxins. Similarly, mycotoxins may be present without visual indicators detected by the naked eye. Laboratory testing is warranted in both cases.

Why all the attention to DON this year? DON is mainly produced from Gibberella/Fusarium ear moulds. High levels of both ear mould and DON in Ontario's corn crop have been detected through OMAFRA's 2018 Grain Corn Ear Mould and Vomitoxin (DON) survey and have been observed in the field in parts of the province. DON is often considered an indicator mycotoxin because the environmental conditions conducive to the development of fusarium and DON are also ideal for the growth of other types of moulds and mycotoxins important to livestock such as zearalenone, fumonisin, and T-2 toxin. The prevalence, potency, and biological effects of mycotoxins vary across mycotoxin types and symptoms of mycotoxin problems can range from reproduction issues, to health issues such as diarrhea and hemorrhaging, and to performance issues such as reduced average daily gain, dry matter intake, and feed efficiency.

Corn Ear Mould.

Corn Ear Mould. Photo credit: Ben Rosser, Corn Industry Program Lead, OMAFRA.

How do feedstuffs become contaminated by mycotoxins?

Moulds and mycotoxins can develop pre-harvest and in storage. They are produced in the field every year; however, the extent to which moulds and mycotoxins develop is dependent on growing conditions within a season. Generally speaking, mould needs a specific combination of moisture, oxygen, temperature, and substrate to grow. Ultimately, high humidity and hot days coupled with cool nights make ideal conditions for mould growth in field crops. There are a couple of ways in which mould spores can enter grain. One way is during pollination where mould spores enter the seed through silk channels. The other is through the seed coat when it becomes damaged by insects, wildlife or by means of other types of physical damage. Moulds and mycotoxins can also develop in other vegetative parts of the corn plant, with mould spores entering the plant through the plant's root system or through physical damage to the plant. This means that mycotoxins can also be present in corn silage, shredlage, cobmeal, etc.

When mycotoxins levels are high in grains, it is also important to pay attention to mycotoxin levels in their related byproducts. This year it means being aware of mycotoxin levels in corn byproducts and co-products such as corn screenings, dried distillers grains with solubles, wet distillers grains, and corn gluten meal. Mycotoxin concentrations increase by two- to threefold in DDGs compared to the grain inputs.

Keep in mind that while the dry conditions during the growing season that resulted in low fungal disease pressure and low levels of mycotoxins in this year's small cereal crops, small grains such as wheat and barley are also vulnerable to mycotoxin contamination when the conditions are right. Fusarium head blight, or scab, is a fungal disease with spores that can produce DON in small cereals. The risk is particularly high when conditions are wet during flowering and grain fill periods.

What are the maximum levels for DON in cattle rations?

The big question for producers is "at what level of DON can I feed cattle without seeing adverse effects"? Unfortunately the answer to this question is not exactly straight-forward. It is well understood that cattle have a lower sensitivity to DON and other mycotoxins than monogastric species, hogs in particular. This is largely thanks to some level of detoxification of DON by rumen microorganisms. In studies conducted in the American Midwest, feeder cattle were fed rations ranging from 13 to 21 ppm DON without any impact to ADG, feed intake, feed efficiency, carcass characteristics, or cattle health. However, it is important to bear in mind that an animal's response to mycotoxins is dependent on a number of factors, including type of mycotoxin, presence of other mycotoxins, immune status of the animal, and time of exposure. Mycotoxins can have additive or synergistic effects, so variability in response to DON may be attributed to the presence of other mycotoxins in the feed, especially considering DON is less toxic than some of the other known mycotoxins. Younger cattle tend to be more susceptible to the effects of mycotoxins than older cattle.

The regulations in relation to DON in animal feed are primarily based on known toxic effects. In Canada the legislated maximum tolerated levels of mycotoxins is based on the "Worldwide regulations for mycotoxins, FAO Food and Nutrition Paper 64, 1997". The Canadian Food Inspection Agency, (CFIA), has set the maximum DON inclusion levels at 5 ppm of the total diet for beef cattle over 4 months of age and at 1 ppm of the total diet for calves less than 4 months of age. The Food and Drug Administration, (FDA), in the US has set DON advisory levels for beef cattle over 4 months of age at 10 ppm on grains and grain by-products and 30 ppm in distillers grains, brewers grains, and gluten feeds and gluten meals derived from grains provided that the total diet for ruminating beef and feedlot cattle older than 4 months not exceed 10 ppm DON. For calves less 4 months the FDA DON advisory level is 1 ppm of the total diet. These advisory levels follow a 2010, Center for Veterinary Medicine (CVM) review of the scientific literature which demonstrated that higher levels of DON in feed for cattle would not appear to present an animal or public health hazard.

A unique lens must be applied when considering the effects of mycotoxins on reproductive cattle because certain mycotoxins can affect reproductive performance. Zearalenone, for example, is linked to reproductive problems in cattle including infertility when it appears in the ration at high levels. While levels of grain corn and byproducts tend to be lower in beef cow rations compared to feedlot rations, consideration must be taken for level of contamination of any grains/byproducts in the ration and mycotoxins that may exist in in corn silage and/or mouldy hay.

What are some important considerations for monitoring and managing DON in cattle rations?

Although it is important to monitor for mycotoxins every year, it is especially important to be vigilant about monitoring and managing mycotoxins in corn and corn byproducts this year, given the high levels of DON detected in this year's corn crop. The first important step in monitoring mycotoxin contamination is taking a representative sample. Because "hot spots" of mycotoxins in a crop, load, or bin can exist, taking spot samples won't give you a good idea of the overall level of mycotoxin contamination in a feed source. A representative sample, taken from a number of subsamples, will provide a better idea of mycotoxin contamination of the greater feed source. Send samples away to an accredited lab for accurate results. Samples can be tested for individual mycotoxins or can be tested as a panel for a number of mycotoxins. A listing of accredited laboratories can be found on OMAFRA's website..

Under ideal circumstances, only clean grain and grain by-products would be fed to beef cattle but this rarely happens under practical conditions. Options for managing high levels of mycotoxins in feed include blending, reducing inclusion rates, and/or using a mycotoxin binder to help mitigate the negative effects of mycotoxins in feed. The effectiveness of mycotoxin binders to bind to a mycotoxin depends largely on the chemical structure of both the mycotoxin and the binder. The shape of the mycotoxin binder must match the shape of the mycotoxin in order that both can "lock" together. Once locked together both binder and mycotoxin are harmlessly excreted in the faeces. Examples of binders include activated charcoal, hydrated sodium calcium aluminosilicate, (HCAS), absorbent aluminum phyllosilicate clay, (bentonite), and large organic polymers such as yeast cell wall. The difficulty in choosing a binder is that binders are very specific to the type of mycotoxin they will bind to. The safety of sodium bentonite and yeast cell wall products as animal feed additives was evaluated by the European Food Safety Authority, (EFSA), and in 2012 delivered its opinion that both products are safe for all animal species, consumers and the environment when used at a maximum level of 20,000 ppm of the total diet.

With higher than average DON in corn and corn byproducts this year, it's important to be on the lookout for mycotoxins in feedstuffs and use appropriate management strategies to avoid any adverse effects of mycotoxins on livestock. Work with your nutritionist or feed representative to help you interpret laboratory results and develop feeding solutions for feedstuffs with high mycotoxin levels.


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