The basics of mycotoxins
Mycotoxins are toxic secondary metabolic products of molds, which negatively impact animal health and productivity. A wide array of grains and forages can be contaminated with mycotoxins and more than 400 mycotoxins have been identified. Not all molds produce mycotoxins and not all mycotoxin-producing molds constantly produce toxins. As a result, mold growth does not guarantee the presence of mycotoxins, but indicates the potential for contamination is there. Mycotoxin producing molds are commonly divided into two categories based on when the mycotoxin is formed: pre-harvest (field fungi) or post-harvest (storage fungi). The Fusarium species of mold are considered field fungi while Aspergillus and Penicillium species are categorized as storage fungi. Exceptions can occur when conditions are right, allowing storage fungi to contaminate crops in the field, and field fungi may continue to produce mycotoxins once crops are in storage. Multiple factors influence mold growth and mycotoxin formation including temperature, moisture content, oxygen levels, and physical damage to the crop. Stress factors, including drought or excessive rainfall, can increase plant susceptibility to mold colonization and mycotoxin formation. Six major mycotoxin categories include: aflatoxins, trichothecenes, fumonisins, zearalenone, ochratoxins, and ergot alkaloids. Additional mycotoxins exist, however, these six categories include the most frequently detected and the most studied. Mycotoxins affect animals in a variety of ways (Figure 1). Many factors influence the impact mycotoxins can have including mycotoxin type, animal species, age of the animal, and the level and duration of exposure to mycotoxins. Environmental conditions, animal health status, and other stresses also play a role in the negative effects mycotoxins have. Some toxins target specific organs such as the liver or kidneys. In general, mycotoxins can cause immune dysfunction, increasing an animal’s susceptibility to disease. High levels of mycotoxins are typically needed for expression of classical mycotoxicoses, but low to moderate levels of mycotoxin contamination can cause subclinical effects which reduce animal health and performance.
Figure 1. Effects of Mycotoxins
Mycotoxins in cattle
Traditionally, cattle were assumed to be less sensitive to mycotoxins as a result of rumen fermentation. However, greater production demands and changes in cattle feeding practices in both dairy and beef herds have increased opportunities for mycotoxins to negatively impact production and animal health.
Focus on deoxynivalenol (DON)
One of the most commonly occurring mycotoxins in livestock feeds is deoxynivalenol (DON), better known as ‘vomitoxin’. The name ‘vomitoxin’ originates from the toxin causing vomiting in swine. Deoxynivalenol is a member of the trichothecene family of mycotoxins, specifically Type B trichothecenes. Several species of Fusarium molds are capable of producing trichothecenes. Additionally, some Fusarium mold species can produce the mycotoxins zearalenone and fumonisins. It is not uncommon to detect more than one toxin in a feed sample since molds can produce more than one type of mycotoxin. Deoxynivalenol inhibits protein and nucleic acid (DNA and RNA) synthesis. The negative effects of DON are mainly seen in the gastrointestinal tract and immune system, but the toxin can cause lesions and necrosis of the skin and mucosa as well. The cells lining the intestines are continuously being renewed and are especially sensitive to the effects of DON. The intestinal epithelium serves two main purposes: 1) to absorb nutrients and 2) to act as a barrier to prevent harmful substances from entering the bloodstream. Both of these functions can be disrupted by DON, leading to reduced nutrient uptake and increased passage of toxins and pathogens into circulation. This can limit animal growth or production capacity as the required nutrients are not absorbed and utilized. Additionally, other organs may be exposed to pathogens or toxins which enter the bloodstream, increasing the possibility for disease. Disruption of the intestinal mucosa can also lead to diarrhea. A large portion of the immune system is located in the gastrointestinal tract. Immune function can be impaired by disruption of the gut mucosa. Additionally, DON can impair production of the white blood cells, which help fight infection. Deoxynivalenol can also weaken the immune system by negatively impacting cytokine and antibody production. The animal’s natural immune response to vaccinations may also be reduced, leaving them susceptible to disease despite vaccination. All of these factors can lead to immune dysfunction in cattle, increasing vulnerability to infections.
Take Home Points
- Even low doses of mycotoxins can negatively impact animal health and productivity
- Mycotoxin contamination can occur in the field as well as during storage
- DON also known as ‘vomitoxin’ can negatively impact more than just gut health
- Testing of feeds can help identify mycotoxin contamination
- Products are available which can help mitigate the negative effects of mycotoxins in livestock
Reducing animal exposure to mycotoxins is key, but not always possible when feeding livestock. Identifying contamination can help to reduce exposure. Unfortunately, mycotoxins are not evenly distributed in feeds, so obtaining representative samples for testing can be difficult. A highly contaminated sample does not mean the entire crop is bad and a ‘clean’ sample does not guarantee that all of the feed is mycotoxin-free. Additionally, many mycotoxins exist, but relatively few are routinely tested for. Although limitations exist, mycotoxin analysis of feeds can provide useful information to producers. Commercial products are available which can bind (adsorb) mycotoxins including clays and yeast products. The chemical structure of the mycotoxin plays a big role in whether the toxin can be controlled well by binders. Additionally, binder products vary in their composition and chemical structure, leading to variability in their effectiveness at adsorbing mycotoxins. Aflatoxins and ergot alkaloids are often controlled well by binders. Other mycotoxins, such as zearalenone and trichothecenes, are not as readily adsorbed by binders. Commercial products which have enzymatic activity can detoxify these mycotoxins by physically altering their chemical structure, leaving inactive or much less toxic substances. Several plant and algae extracts have been identified which can help reduce damage to the liver and provide support to the immune system. Combination products can provide broad spectrum mycotoxin control.
This article was originally published in Progressive Cattleman.