Molds and Mycotoxins - Effects of Moldy Feed and Mycotoxins on Cattle

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"Differences of opinion exist regarding the role of molds and mycotoxins in livestock problems basically because their effects on animal health and production are still in a grey area". (Seglar & Mahanna, 1995).

"Mycotoxins can have a very pervasive, yet subclinical effect on both performance and health in ruminants that can easily go unnoticed. If you wait until clinical symptoms of mycotoxin problems are obvious, you no doubt waited too long". (Eng, 1995).

Effects of Mold

  • Moldy feeds are less palatable and may reduce dry matter intake. This in turn leads to a reduction of nutrient intake, reducing weight gains or milk production. Performance losses of 5 - 10% are typical with moldy feeds even in the absence of mycotoxins. Mycotoxin contamination increases production losses, even when mold is not readily visible.
  • Moldy feed may have reduced digestibility and energy content may need to be adjusted down by 5%. Molds grow and propagate deriving energy from the feed's protein, fat and carbohydrate. Dietary fat in particular is reduced in mold infected feeds. Suggested that book values for energy be multiplied by 0.95 in the presence of substantial amounts of mold (ie 95% of energy value). Some researchers suggest reducing energy by as much as 10% (ie 90% of energy value).
  • Moldy feeds may cause health problems. Feeding moldy feeds increased problems with mycotic abortions and respiratory disease. Feeding cattle moldy feeds is also hazardous to human health - farmers lung may result from breathing in mold spores.

Moldy Feed and Mycotoxins

  • Mold spore counts may underestimate the amount of mold present and be a poor indicator of the potential risk.
  • Moldy or musty feed will not always contain harmful mycotoxins. Moldy feeds may contain mycotoxins but not at harmful levels.
  • Molds may produce harmful levels of potent mycotoxins under certain circumstances. Molds may always produce some mycotoxins.

Effects of Mycotoxins

  • Initially mycotoxins cause relatively minor problems. The reduction in performance may be negligible. Within days or weeks, the effect of continued mycotoxin consumption on performance (milk production or weight gains) becomes more pronounced.
  • Off-feed, ketosis and displaced abomasum problems may increase significantly with the consumptions of mycotoxins. Some animals develop diarrhoea or have signs of haemorrhaging.
  • Estrogenic effects, swollen vulvas and nipples; vaginal or rectal prolepses may occur. Reduced fertility / conception rates or abortions may also be evidence of mycotoxin consumption.
  • The effects of mycotoxins are amplified by production stress. High producing dairy cows and rapidly growing feedlot cattle are more susceptible to the effects of mycotoxins than low producing animals.

Problems with Mycotoxins

The severity of mycotoxins problems in cattle from field cases are not readily replicated in controlled research trials:

  • DON levels at 0.1 ppm have been linked with depressed feed intake and lower milk production on dairy farms but research on dairy cows 13 - 22 weeks into lactation with 0, 6 and 12 ppm DON did not show significant differences in milk yield.
  • Case studies from University of Wisconsin noted bovine abortions associated with 1 ppm Zearalenone but similar reproductive disorders could not be demonstrated in cattle fed 200 - 300 ppm Zearalenone contaminated feed.

Research and field data on the effects of molds and mycotoxins are highly variable and often contradictory. Possible reasons for this are:

  • Detected mycotoxins may simply act as indicators of other harmful but unknown mycotoxins and/or metabolites.
  • Currently there is no way to tell at what level these other compounds are present.
  • Many trials are conducted with essentially "pure" mycotoxins and no other measurable toxins. Performance and health were not affected in feedlot cattle fed 10 to 15 ppm DON in the diet provided little or no other mycotoxins were present.
  • The cumulative and/or synergistic effects of mycotoxins and metabolites are unknown, but suspected as a mode of action.
  • Duration of the tests; many conducted for 1 to 10 days; several for only a month.
  • Trials with single dose rate that did not reflect expected levels in practice.
  • Animals used were the least sensitive, ie mid to late lactation cows producing 20 kg milk.

Detoxification of mycotoxins

Ruminants are uniquely equipped to protect themselves from the harmful effects of mycotoxins. It is assumed that sufficient degradation of the mycotoxins has taken place before absorption into the blood and vital organs to protect the animals.

Mycotoxins are detoxified or altered in the rumen, but:

  • The rate of detoxification differs for the different types of mycotoxins.
  • The extent of detoxification of any particular mycotoxin depends on the rate of passage of feed. Rumen turnover rates are about 8 times longer in beef cows than lactating dairy cows.
  • The extent of detoxification depends on the original dose level. Five and 10 ppm DON were completely transformed to the reportedly less toxic deepoxy DON or DOM-1 within 24 hours when incubated in rumen fluid. More than half of the DON remained from the 50 and 100 ppm DON treatments at 24 hours incubation.
  • The altered metabolite(s) may be more toxic than the original mycotoxin. Work in sheep had Zearalenone transformed into the reportedly more toxic Zearalenol.

Bottom line on molds and mycotoxins in ruminant rations:

  • Effects of molds and mycotoxins on ruminants are highly variable in practice. It is impossible to predict the effects that molds or mycotoxins are likely to have in an individual situation.
  • Ruminants are less sensitive and/or affected by molds and mycotoxins than swine.
  • Ruminants are able to detoxify or transform mycotoxins to other metabolites, mostly less harmful.
  • Ruminants are nevertheless susceptible to the deleterious effects of molds and mycotoxins in feed.
  • Young pre-ruminant and high producing cattle are the most susceptible to the effects of mycotoxins.
  • Decreased feed intake, production losses of 5 - 10% and reduced reproductive performance are the most typical symptoms of a mold and mycotoxin problem.
  • If molds and/or mycotoxins are present it is prudent to take steps to limit their potentially harmful effects on ruminants.

Preventing Mycotoxicoses

  • The confirmed presence of mycotoxins is a concern for chronic dairy cattle health and production problems, and in some cases human health concerns as toxin residues (such as aflotoxin in particular) may be present in milk.
  • There are many different types of mycotoxins and they are very stable.
  • Laboratory test results should be interpreted in consultation with your nutritionist because of the numerous types of mycotoxins, and their potential toxic effects, which can depend on the concentration of the toxins present.
  • Several types of products have been used to help prevent the absorption of mycotoxins in the gut to prevent symptoms of mycotoxicoses, including both inorganic and organic-based products.
  • Inorganic products include things like silicate minerals (e.g. bentonite clay or aluminosilicates) and activated charcoal but relatively large quantities need to be consumed to be effective.
  • The inorganic products have shown some benefit, particularly for aflatoxins, but the results are inconsistent (Diaz and Smith, 2005).
  • Organic products include polymers of glucomannan, which is a complex carbohydrate obtained from yeast cell wall. Glucomannan polymers have a high adsorptive capacity for mycotoxins and can normally be included at lower levels in the diet than the inorganic products (Diaz and Smith, 2005).
  • Recent research at the University of Guelph indicated that cows given a polymeric glucomannan product from yeast while consuming Fusarium contaminated grains had higher serum IgA concentrations (indicator of immune status) than the cows eating the same grains in the trial that did not receive this product (Smith et al., 2006).
  • No single product is effective against all known compounds (Huwig et al., 2001)


  1. Diaz, D. E. and T. K. Smith. 2005. Mycotoxin sequestering agents: practical tools for the neutralisation of mycotoxins pp. 323-339 in: The Mycotoxin Blue Book. Ed. D. Diaz. Nottingham University Press, Nottingham, United Kingdom.
  2. Huwig, A., S. Freimund, O. Käppeli, and H. Dutler. 2001. Mycotoxin detoxication of animal feed by different adsorbents. Tox. Lett. 122: 179-188.
  3. Smith, T.K., G. Diaz-Llano, S.N. Korosteleva, and M. Yegani. 2006. The effect of feed-borne Fusarium mycotoxins on reproductive efficiency in dairy cows, sows, and broiler breeders pp. 367-372. in: Nutritional Biotechnology in the Feed and Food Industry. Eds. T.P. Lyons, K.A. Jacques, and J. M. Hoover. Nottingham University Press, Nottingham, United Kingdom.

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Tom Wright - Dairy Cattle Nutritionist/OMAFRA

Creation Date: 14 August 1996
Last Reviewed: 29 July 2013