Grading tolerances for fusarium-damaged grain and DON feeding guidelines

Fusarium Head Blight

Fusarium Head Blight (FHB) is a fungal disease of cereals.

FHB most often infects wheat, but barley, oats, rye, corn, canary seed and forage grasses are also susceptible. In wheat, it is characterized by chalky kernels which appear thin and shrunken. Infected kernels also have a white or pinkish fibrous mould in the crease area, and sometimes in the germ of the kernel. In barley, infected kernels are encrusted with pink, orange or black fusarium mould. Under magnification, the black encrustations appear raised above the surface of the kernel and are surrounded by a white mould.

Depending on the species of Fusarium infecting the seed, FHB may produce mycotoxins, the most common of which is deoxynivalenol (DON), also known as vomitoxin. DON is a mild toxin compared to other toxins which can be found in grains and forages. Reduced feed intake and the accompanying decrease in performance are the only symptoms of DON toxicity livestock producers are likely to encounter.

Various federal, provincial and grain industry organizations are working together to assist producers and ensure the smooth functioning of Canada's grain quality assurance system. Following is a summary of programs and information provided by various agencies which will be of interest to grain producers, marketers and buyers. If you require additional information, please call the contacts.

Grading tolerances

Grading tolerances for fusarium-damaged grain - Canadian Grain Commission

• Tables of allowable levels of fusarium-damaged kernels for:
  • Western Canadian wheat at primary elevators
  • Eastern Canadian wheat at primary elevators
  • Canadian barley at primary elevators
  • Canadian rye at primary elevators

Delivery procedures - Canadian Wheat Board

As in past years, the Canadian Wheat Board (CWB) will offer a delivery program for fusarium-affected wheat.

Under the program, certain classes and grades of wheat with fusarium damage above the tolerance levels will be accepted at country elevators. In this way, farmers will be paid a price which reflects the quality of their high-grade wheat, minus a discount for the weight of fusarium content which exceeds the tolerance level. However, the volume of grain allowed to be shipped by an elevator under the program may be limited.

Effective August 1, 1999, the classes and grades of wheat which will be accepted with up to five per cent fusarium damage include: No. 2 and 3 Canada Western Red Spring, No. 2 Canada Prairie Spring Red, No. 2 Canada Prairie Spring White, No. 2 Canada Western Extra Strong and Nos.. 3 and 4 Canada Western Amber Durum (CWAD).

For all other grades, the Canadian Grain Commission's primary grade tolerances for wheat affected by fusarium will apply.

DON feeding guidelines

Feeding livestock FHB affected grain. Guidelines - Manitoba Agriculture

The presence of DON in fusarium affected grain can cause livestock feeding problems. Different livestock species respond differently to DON. The effects of DON on different livestock species and the Agriculture and Agri-Food Canada guidelines for DON intake are discussed below.

Swine

Agriculture and Agri-Food Canada Guideline: 1 ppm

Feeding DON at levels above 1 ppm in the complete feed will result in some degree of feed refusal. Producers can expect to see feed refusal of about 5 per cent when levels of 1-2 ppmDON are fed and feed refusal of 25 per cent with DON levels of 4 ppm. At 10-20 ppm DON, complete feed refusal may occur. Vomiting seldom occurs but has been reported at high DON intakes (20 ppm).

Weanling pigs are more susceptible to the effects of DON and may exhibit feed refusal with dietary concentrations of less than 1 ppm. If possible, avoid using DON-contaminated grain in rations for weanlings.

Although DON does not appear to have a strong effect on reproduction, the effects of feeding DON on reproductive performance are not fully known. The use of DON in rations for gestating and lactating sows should, therefore, be avoided or minimized. Keeping DON levels below 1 ppm will minimize the chance of reproductive problems occurring.

Dairy cattle

Agriculture and Agri-Food Canada Guideline: 1 ppm

Until 1993, very few feeding trials had been conducted with lactating dairy cows. Recent research, however, has indicated that dairy cows may be able to tolerate higher levels of DON. In an Agriculture and Agri-Food Canada trial, cows were fed rations containing 6.4 ppm DON for 10 weeks with no effect on production. Research at the University of Manitoba showed that feeding 8.4 ppm DON had no effect on dry matter intake or milk yield of cows producing over 33 kg milk/day.

Growing beef cattle/sheep

Agriculture and Agri-Food Canada Guideline: 5 ppm

Growing-finishing cattle and lambs can tolerate much higher levels of DON in their diet without going off-feed. Some research has shown that feeding 15 ppm DON to feeder lambs for 4 weeks had no effect on feed intake or gain. In a University of Minnesota feeding trial (1993-94) steers were fed rations containing up to 18 ppm DON through the finishing phase with no effect on gain, feed intake or feed efficiency. A North Dakota State University (NDSU) trial (1993-94) fed up to 9 ppm DON during the growing phase and up to 12 ppm during the finishing phase with no effects on performance.

Pregnant cows/ewes

Based on trials conducted since 1993, it appears that, at levels tested, DON has no effect on reproductive performance. NDSU fed heifers rations containing 10 ppm DON, on a dry matter basis, during mid and late gestation. No differences in feed intake, gain, calving rate or calf birth weights were observed. This is similar to results obtained with sheep at the Universities of Manitoba and Minnesota where ewes were fed up to 12 ppm DON during late gestation with no effect on the number of lambs born, percentage born alive or lamb birth weights. The University of Minnesota also fed ewes a diet with 7 ppm DON from 10 days before breeding until 30 days after breeding with no subsequent effect on reproductive performance.

Horses

Agriculture and Agri-Food Canada Guideline: 1 ppm

No information is available on feeding DON-contaminated grain to horses. The use of the feeds should be minimized whenever possible.

Poultry

Agriculture and Agri-Food Canada Guideline: 5 ppm

Poultry are the livestock species most tolerant of DON. Some studies show that feeding 20-50 ppm DON has no effect on production.

Interpreting the guidelines

The above guidelines for DON intake are given on a 100 per cent dry matter basis and refer to the complete ration. This would include the forage component of cattle rations. For example, grain with a DON level of 15 ppm could meet the guideline for growing cattle if it makes up one-third of the animal's total dry matter intake. The remaining two-thirds of the ration could be forage.

Several factors, including stress and the presence of other mycotoxins, can influence an animal's response to DON. Stressed animals are more susceptible to the effects of mycotoxins and may react negatively to lower levels of DON. Some common sources of stress are:

• High levels of production.
• Poor health of animals.
• Less than optimum feeding programs.
• Overcrowding and other housing conditions.

Mycotoxins can act in a synergistic manner and the presence of other mycotoxins may cause an animal to show toxicity symptoms at lower than expected dietary levels of DON. DON is considered to be a "marker" toxin indicating the potential presence of toxins which have not yet been identified. Although the "marker" may not be toxic to a particular species, the unidentified toxin(s) could cause a negative response.

It is difficult to extrapolate precise feeding recommendations from research data for several reasons. Purified DON may be used in research. This is not as toxic as the naturally occurring DON, likely because of the absence of other DON metabolites. Research trials are also run in controlled environments with a minimum amount of stress and optimum feeding programs.

Tissue residues

When higher levels of DON-contaminated grain are fed to the more tolerant livestock species, the concern shifts from the effect on animal performance to the potential accumulation of DON in edible products, i.e., meat, milk and eggs. Numerous research trials have shown that tissue residues of DON are not a concern. DON is rapidly metabolized by animals and there is no extensive uptake or retention of DON by any animal tissues.

Detoxifying DON

A number of chemical and physical treatments have been looked at as potential methods of detoxifying DON. Unfortunately, there is no easy way to reduce the toxicity of DON-contaminated grain other than removing the contaminated kernels.

A hydrated sodium aluminum silicate (HSAS) product has been marketed in Manitoba as a possible detoxifying agent. HSAS is sold under a variety of brand names and is used in the feed industry as a anti-caking agent. HSAS does not appear to be effective in binding significant amounts of DON.

DON and straw

A joint study between Manitoba Agriculture and the CGC showed that DON is usually found almost entirely in fusarium-damaged kernels. In most samples negligible levels are found in non-damaged kernels and in the stem. The amount of DON in cereal straw will depend primarily upon the presence of contaminated grain and chaff. Straw with a high concentration of this material should not be fed to horses or used as bedding for hogs.

The quick test (ELISA) for analyzing DON in straw appears to be unsatisfactory. Producers should test straw at a laboratory that uses as chromatography-mass spectrophotometer methods.

DON and greenfeed/silage

DON levels peak two to three weeks prior to seed maturity and then start to decrease. Because greenfeed and silage are harvested prior to the seed being completely mature, the level of DON in the harvested material could be significantly higher than that found in threshed grain. These levels will, however, be blended down through the contribution of leaves and stem. The leaves and stem do not produce any significant amount of DON.

Ensiling, if done correctly, will prevent further mould development. It is essential that the silo be airtight. Ensiling will not destroy any DON present in the seed prior to ensiling.

DON and high moisture grains

High moisture grains may also be a concern because they too are harvested prior to maturity. The level of DON is not, however, blended down by the stems and the leaves.

Using DON test results

DON analysis of fusarium-infected grains is an important part of planning a safe feeding program for livestock. It is even more important that producers continue to monitor livestock and take action if feed refusal occurs.

Feed analysis, whether for nutrient content or mycotoxin content, is meant to be used only as a guideline when preparing livestock rations. A close watch still needs to be kept on the animals. A drop in feed intake may indicate that DON levels are higher than they should be.

DON test results is common because the mycotoxin being detected is not uniformly distributed. It is common for DON levels in grain to fluctuate within the same field (i.e., field margin to centre) as well as between fields. In addition, DON is not distributed uniformly throughout every seed. This could lead to different DON test results even within what appears to be approximately the same sample.

Contacts

Canadian Grain Commission

Contact Service Centre nearest you

Contact Regional Center nearest you

Or call 1-800-853-6705

Canadian Wheat Board

Call 1-800-275-4292

Manitoba Agriculture

Karen Dupchak
Provincial Livestock Nutritionist
(204) 945-7668