Molds and Mycotoxins - Feeding Mold and Mycotoxin Contaminated Wheat to Ruminants

Acceptable levels of normal uninfected wheat for ruminants

• lactating dairy cows, 15 - 20% of total ration dry matter (TRDM)

• lactating dairy cows, 25 - 40% of grain ration

• feedlot cattle, up to 40% of TRDM

• sheep, up to 40% of TRDM

The practical level of wheat in a ration depends on several factors

• the cost of wheat relative to other grains.

• the other grains being fed; in particular how rapidly their starch breaks down in the rumen.

• the type and level of forage fed; in particular forage particle length.

• the feeding sequence, amounts fed per feeding or meal and bunk/manger management.

• the inclusion of buffers, sodium bicarbonate and/or magnesium oxide.

• the inclusion of an ionophore, Rumensin, Bovatec or Posistac.

• the inclusion of calcium carbonate.

• the mycotoxin levels in wheat will influence the acceptable amount in a ration.

Agriculture and Agri-Food Canada guidelines for DON (Vomitoxin) in animal feeds

• pigs, calves, lambs, lactating cows and lactating ewes, 1 ppm in the diet.

• adult cattle, adult sheep and poultry, 5 ppm in the diet.

Initial corrective steps for Fusarium infected wheat

• clean moldy grains, remove fines and light weight grains suspected of mycotoxin contamination.

• Reduce the energy levels of moldy wheat or light weight grains by 5 - 10% and reformulate rations. Observe the limits on wheat.

• dilute mold or mycotoxin contaminated wheat with mold-free grains.

• if moderate effects on animals are noted, reduce the inclusion of the suspected wheat by 50% of the amount in the ration.

• if effects on animals are severe, discontinue use of the wheat for at least a week. If improvements are noted, sample the wheat and have it retested to determine the safe level to feed.

Sampling method for dry feeds (Penn State University)

• Take 8 - 12 samples at each of 3 - 5 feedings or feed removal from storage or take 12 - 20 stream samples from an entire delivery, or 12 - 20 deep probe samples from a bin. Include samples from the sides of bins or edges of storage where mold is likely to occur.

• Mix the subsamples well, take a 500g composite sample for submission to the laboratory. Some labs recommend taking a composite sample of 1 kg for mycotoxin analysis.

• Keep an additional 500g sample for confirmation or other analyses.

• Store all samples in clean double layer paper (grocery store) or cotton bags. Store in a cool dry place. Submit to the lab as soon as possible.

• Always check the basis on which results are given - often they are on a as-fed basis. Correct these to a dry matter basis so that inclusion rates can be calculated. eg. Wheat with 15% moisture analyzed at 5 ppm DON as-fed. 100 - 15 = 85% dry matter 5 / 0.85 = 5.9 ppm DON on a dry matter basis.

• Results may be expressed in a number of different ways. Note that ppm = mg/kg = ug/g. Also 1,000 ppb = 1 ppm.

Calculate the maximum inclusion levels of moldy wheat

• In the total ration dry matter safe level in TRDM level in wheat DM x 100 = % maximum inclusion rate eg. for lactating cows - maximum level DON is 1 ppm; if wheat analysis is 5 ppm DM then: 1 / 5 x 100 = 20% maximum inclusion level in TRDM based on DON level. This does not exceed the nutritional limits listed above. Wheat DON levels above 5 ppm will reduce the maximum inclusion level below 20% wheat in TRDM.

• In grain rations for lactating cows, use the maximum grain level fed not the average. The average ration may be 50% grain, but early lactation cows may be up to 60% grain. eg. for lactating cows - maximum level DON is 1 ppm; if wheat analysis is 5 ppm DM then:
  a) 1 / 5 x 100 = 20% maximum inclusion level in TRDM.
  b) 20% / 0.6 = 33% maximum wheat in the grain ration. This is within the acceptable range given above.

• In feedlot cattle that tolerate a maximum of 5 ppm DON in the TRDM, wheat DON levels above 12.5 ppm will reduce the maximum inclusion level below 40% wheat in TRDM.

• Use the limits for the other toxins analyzed and follow the same calculations as above to determine if they may be more limiting to acceptable inclusion rates for wheat.

• Despite these calculations, poor palatability of moldy wheat may lower feed intake. Palatability of the wheat may ultimately determine acceptable inclusion rates. If in doubt, err on the conservative side and watch for problems! Wheat must always be introduced into the ration gradually.

Practical steps that may help

• Include aluminosilicate or bentonite in ruminant rations at 0.5% (or follow manufacturer's recommended rates) to reduce the effects of mycotoxins. These compounds may bind mycotoxins in the digestive tract and reduce their absorption. They are most effective against aflatoxin and less effective on other mycotoxins.

• In an attempt to alleviate the effects of mycotoxins, increase the levels of Vitamins A, and E and trace minerals Selenium, Zinc, Copper and Manganese. There are only anecdotal suggestions that levels be increased by up to 25%. Note any overriding considerations; eg. copper levels in sheep rations.

• Add an appropriate mold inhibitor (sodium or calcium propionate or organic acids) to stored grain to prevent further development of molds.

• add 0.2 to 0.25% to non-ensiled feeds with 14 - 17% moisture

• add 0.5 to 0.6% to non-ensiled feeds with 18 - 24% moisture (or follow the manufacturer's recommendations).

Watch these potential pitfalls

• Mycotoxins tend to be concentrated in the red dog, husk, light grains, and broken kernels. Mycotoxins may be as much as five times higher in the screenings compared to the grain. This may be a year to be extra careful feeding "grain screenings".

• Mycotoxin contaminated wheat that may be used in the fermentation industry poses a potential problem. The fermentation process does not break down the mycotoxins. Mycotoxin concentration increases in the distillers by-products. Check your source of distillers grains for the type of grain used.

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