Compiled and shared-
Dr Rajesh kr singh, jamshedpur, jharkhand, India,9431309542
rajeshsinghvet@gmail.com.
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 can be 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. 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 of mycotoxins. Some toxins target specific organs such as the liver or kidneys.
In general, mycotoxins can cause immunosuppression, increasing an animal’s risk of disease. High levels of mycotoxins are typically needed for expression of classical mycotoxicoses, but low to moderate levels can cause subclinical problems that are less easily detected and reduce animal performance.
Mycotoxins in cattle
Mycotoxins are a very common feature of feed. Whether these toxins have been produced by fungi infecting crops in the field or by fungi contaminating feed in storage, they pose a challenge to livestock. Compared to other animals, the rumen makes a big difference to the challenges that ruminants face from mycotoxins. Some rumen microorganisms can naturally detoxify some mycotoxins, but others can turn some into more potent forms and quite a few mycotoxin types simply pass right through the rumen. Unfortunately, many mycotoxins reduce the ability of the rumen to function well.
Some DON degradation
The rumen is the powerhouse of a ruminant. The microorganisms within the rumen convert fibrous forage into a valuable source of energy, protein and other nutrients. Some of these same fiber-digesting microorganisms are also able to act on the complex chemicals of mycotoxins. Deoxynivalenol (DON), perhaps the most prevalent major mycotoxin in the world, is also susceptible to the action of some fiber-digesting rumen bacteria. This is a bonus for animals faced with the regular mycotoxin challenge in the feed, but the natural action is not always effective and not fast enough to prevent effects in the rumen itself.
The presence of DON in the feed has been correlated with significantly reduced milk productions. DON (a type B trichothecene) has also been shown to affect rumen microbial processes such as reducing the availability of nitrogen (microbial N). So the effects can be seen even if there is degradation of DON over time in the rumen. The other consideration is that the amount of DON naturally degraded in the rumen depends on the activity of quite specific fiber-digesting microorganisms. Under conditions of SARA or generally high grain/concentrate and low forage, a higher proportion of trichothecenes can escape the rumen and cause damage elsewhere. Damage is again typically more obvious (including gut wall lesions) in sheep and goats, and of course in calves prior to the establishment of the rumen. Calves can struggle with scours and respiratory diseases due to the effects of trichothecenes on the immune system. In dairy cows, the damage is more likely to be subclinical or indirect issues such as effect on intestinal wall permeability (lowering the defence against pathogens and reducing nutrient uptake), reduced productivity, higher somatic cell count issues, and risk of mastitis and metritis.
Ochratoxin A
There can be an almost complete detoxification of ochratoxin A (OTA, an occasional storage mycotoxin), though A portion of OTA is known to be able to escape detoxification through rumen bypass. Up to 10% of the OTA challenge has been reported to pass through unchanged in the goat rumen (and sheep are likely to be similar). This happens to a lesser extent in cows since they have a larger rumen with a longer transit time. With high feed intake and stress factors, however, more rumen bypass can occur reducing mycotoxin breakdown.
Aflatoxin carryover
Aflatoxins are also partially degraded in the rumen and the remainder biologically converted in the liver to Aflatoxin M1 which is still bioavailable and unfortunately can carry over into the milk produced. Because of the milk safety problem of aflatoxin M1, aflatoxins receive perhaps the most attention of all mycotoxins in dairy production. Other mycotoxins are able to have a less obvious but still economically significant impact on the performance of dairy cows.
Zearalenone and reproduction issues
The main effect of zearalenone (ZEN) and related compounds in animals is estrogenic. The ZEN molecule fits to the estrogen receptors triggering the wrong hormonal responses and upsetting the reproductive system. ZEN is biologically converted in the rumen largely to alpha-zearalenol (α-ZOL) and this is a much more potent form that fits more easily to the estrogen receptors than ZEN itself. So ruminants are susceptible to the effects of ZEN. ZEN is also known to increase the effect of DON on the gut wall. Action of the epoxidase enzyme in Mycofix on trichothecenes such as DON (which is transformed into non-toxic DOM-1). This transformation takes place rapidly helping protect the rumen and the microorganisms.
Ergot alkaloids
Ruminants also have a well-known susceptibility to the effects of ergot alkaloids. These can be formed either from ergots growing on cereals or from endophyte fungi within tall fescue grass. One of their main effects is vasoconstriction (restricting blood flow) which has an impact on hoof health, heat stress, mastitis and reproduction amongst other symptoms.
Silage mycotoxins
Ruminants can also face a challenge from a diversity of silage mold mycotoxins. These have been shown to reduce rumen function, cause scours and reduce milk production as well as specific symptoms according to the mycotoxin type.
Solving mycotoxins
Because of the effect of mycotoxins on rumen function and the gut wall, an effective mycotoxin deactivator should be able to act within the rumen. Effective binding is important for aflatoxin but should be specific enough that vitamin uptake is not reduced at the rate used. Mycofix® achieves this with the only binder to successfully go through the EU process of authorization. This binding has also been demonstrated effective against ergot alkaloids and some of the troublesome silage mold mycotoxins as well as endotoxins produced by gram negative pathogenic bacteria in the gut. Even so, binding is just part of the solution.
Dealing with common DON and ZEN presence in feed requires effective biotransformation and this starts in the rumen with the unique enzyme approaches of Mycofix. Protection for the gut wall, liver and immune system is also provided by proven biological protective ingredients to provide the complete package of mycotoxin protection.
Traditionally, cattle were assumed to be less sensitive to mycotoxins as a result of rumen fermentation. Rumen microbes are, however, ineffective at degrading some types of mycotoxins such as ergot alkaloids and, in the case of zearalenone, potency can actually be increased by changes in the rumen (through formation of alfa-zearalenol).
Furthermore, 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
One of the most commonly occurring mycotoxins in livestock feeds is deoxynivalenol, 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 deoxynivalenol 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 deoxynivalenol.
The intestinal epithelium serves two main purposes: to absorb nutrients and to act as a barrier to prevent harmful substances from entering the bloodstream. Both of these functions can be disrupted by deoxynivalenol, 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 optimally 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, and immune function can be impaired by disruption of the gut mucosa.
Additionally, deoxynivalenol 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 immunosuppression in cattle, increasing vulnerability to infections.
Managing mycotoxins
Reducing animal exposure to mycotoxins is key but not always possible when feeding livestock. Identifying contamination is needed to help 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 so combination products are required for broader spectrum control of mycotoxins.
Some commercial products can achieve this by including enzymes (or micro-organisms that produce enzymes) to detoxify mycotoxins by altering their chemical structure, leaving essentially non-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 of binding, enzymes and protective plant and algal extracts can provide broad spectrum mycotoxin control.
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.
Deoxynivalenol (aka 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
