13 Jul 2023
Mycotoxins in animal nutrition: A review
Mycotoxins are secondary metabolites produced by molds, primarily belonging to the three genera Aspergillus, Penicillium, and Fusarium. They are produced in cereals and forages before, during, and after harvest, under various environmental conditions.
Mycotoxins are produced by various fungi, particularly by many species of Aspergillus, Fusarium, Penicillium, Claviceps, and Alternaria -Bennett and Keller, 1997. Mycotoxins generally exhibit significant chemical heterogeneity, and approximately 400 of these fungal metabolites are considered toxic -Moss, 1996. It is likely that all fungi produce mycotoxins when growth conditions are favorable. Mycotoxins can be carcinogenic, neurotoxic, and teratogenic -International Agency for Research on Cancer, 1999; Abdel-Wahhab et al., 1999a, b, 2004).
Some of the most common mycotoxins are: aflatoxins, ochratoxin A (OTA), zearalenone, and fumonisins.
Accurate control of mycotoxin contamination and the transfer of mycotoxin-related compounds through the food chain is crucial-Ramos and Hernandez, 1996, as even small amounts of mycotoxins can lead to allergies, diseases, skin rashes, neurotoxicity, and other health issues.
Although mycotoxins are generally less acutely toxic than botulinum toxin -Moss, 1996, the consumption of a diet contaminated with mycotoxins can have chronic, acute, and long-lasting effects. These effects can include teratogenic and carcinogenic impacts (particularly affecting the liver and kidneys), estrogenic effects, and immunosuppression in both animals and humans. Animals often suffer more due to the consumption of lower-quality grains -Casteel and Rottinghouse, 2000.
Mycotoxins can infiltrate the food chain through different pathways, but they can be categorized into two main routes of contamination: direct and indirect contamination –Jarvis, 1990.Direct contamination occurs when molds grow within the food material itself. Almost all food items are susceptible to mold growth at some point during production, processing, storage, or transportation. Mold growth in food that is consumed directly can lead to direct exposure to mycotoxins.
Level of Feed Contamination in Ruminants
Molds have the ability to grow on plants either in the field or during storage. These fungi can produce toxins that may pose risks to humans and animals when consuming the contaminated produce. While such instances of poisoning can be lethal for animals, they are seldom fatal for humans -Pfohl-Leszkowicz, 2000.
The historical records of humanity clearly indicate the existence of mycotoxicological risk since the early stages of organized agricultural production –Pittet, 1998. References in the Old Testament to ergotism –Schoental, 1984, and the role of fusarium toxins, such as toxin T-2 and zearalenone, in the decline of Etruscan civilization –Schoental, 1991, as well as the Athenian crisis in the 5th century BC –Schoental, 1994, are noteworthy. Furthermore, it is believed that certain Egyptian tombs contain ochratoxin A, which is linked to the mysterious deaths of several archaeologists –Pittet, 1998.
Forages and cereals naturally come into contact with fungal spores before, during, and after harvest, as well as during transportation and storage. Mold growth is controlled by a series of physicochemical parameters including the amount of free water (aw), temperature, presence of oxygen, nature of the substrate, and pH conditions -Nelson, 1993.
Contamination can be facilitated by rodents, birds, and insects, which can cause physical damage to plants and create entry points for fungal spores –Pfohl-Leszkowicz, 2000.
Fungi & Mycotoxins in Forages
Grasslands have been found to harbor various fungi, including Claviceps, which is responsible for ergotism, Pythomyces, which produces sporidesmin causing facial eczema, Neotyphodium causing dry gangrene, and Rhizoctonia producing slaframine causing sialorrhea in ruminants –Le Bars and Le Bars, 1996. The most commonly encountered mold in the field belongs to the Fusarium genus. While this fungus primarily infects cereals, it can also be present in forages in the field and post harvest. Depending on the species and environmental factors, Fusarium sp. can produce trichothecenes, zearalenone (ZEN), and/or fumonisins.
When hay is harvested under optimal conditions, it develops a limited and harmonious microbial community. This occurs through the sequential presence of three ecological types of fungi: field fungi before harvest, intermediate fungi during harvest, and storage fungi after harvest.
In harvested hay that is stored under moist conditions, there is a higher abundance and variety of intermediate and storage fungi – as observed by Pelhate in 1987. Among these, hydrophilic and heat-tolerant species like Aspergillus fumigatus, known for respiratory complications and potential gliotoxin production, and Stachybotrys atra, which produces satratoxins G and H leading to stachybotryotoxicosis, are particularly prevalent.
Numerous highly toxigenic species of Aspergillus and Penicillium have been found in moist hay and straw –Clevstroem et al., 1981, as well as in Fusarium sp. that produce ZEN -Scudamore and Livesey, 1998. As a result, a wide variety of toxins, including harmful PAT, aflatoxins, and sterigmatocystin, can be found in inadequately dried hay and straw.
Molds and mycotoxins in feed concentrates
As cereals are consumed by both humans and animals, they serve as the primary carriers of mycotoxins. Shockingly, between 25% and 40% of cereals worldwide have been found to be contaminated with mycotoxins, according to Pittet’s research in 1998.
The most dangerous of these toxins include aflatoxins produced by Aspergillus flavus and Aspergillus parasiticus. These two fungi are storage molds often found in cereals, peanuts, cotton, and oilseed products from warm and humid countries.
While mycotoxins do not have a significant impact on plants cultivated in temperate regions, they do pose a threat to imported food. To ensure consumer safety, the European Commission has established strict limits of 0.005 ppm for AFB1 (aflatoxin B1) in cereals or concentrated products.
Ochratoxin A (OTA) produced by Penicillium viridicatum may be present in all cereals. It is mainly found in maize, barley, oats, rye, and wheat, as well as in oilseed products, particularly if the products were poorly dried before storage. OTA is synthesized after harvest, which is the predominant phase of food contamination.
Trichothecenes such as DON, diacetoxyscirpenol (DAS), T-2 toxin, and HT-2 toxin produced by Fusarium sp. may be present in most cereals during harvest and storage. Fusaric acid, which is often present in cereals, increases the toxicity of trichothecenes through a synergistic mechanism –Scudamore and Livesey, 1998.
Zearalenone (ZEN) is primarily present in maize. However, it can also be found in small amounts in sorghum, sesame seeds, barley, late-harvested wheat and oats, and grains that have suffered seed coat damage.
Fumonisins (FB1, FB2, FB3) are mainly associated with corn and have a lesser impact on wheat. Oilseed products, grains, and cakes currently used in animal feed can also be contaminated by all three fungal genera, Aspergillus, Fusarium, and Penicillium. However, mycotoxins produced by these molds are partially destroyed during oil extraction and further destroyed during industrial processing.
Mycotoxins & animal health
Fungal toxins produce an array of detrimental consequences in animals,as well as putting humans at risk. The economic ramifications of reduced productivity, subtle yet persistent harm to critical organs and tissues, heightened susceptibility to diseases due to immune suppression, and disruption of reproductive capacities far outweigh the impact of immediate livestock mortality.
LMycotoxins can be categorized based on the specific organ systems they target. Each mycotoxin directly or indirectly affects at least one system within an animal’s body, acting as a mechanism of toxicity. Notably, certain crucial mycotoxins can impact the same system, such as the immune system, and a single mycotoxin can simultaneously affect multiple systems within the body.
- Mycotoxins generally exhibit great chemical heterogeneity, and approximately 400 of these fungal metabolites are considered as toxic.
- The metabolism of mycotoxins is complex and involves bioactivation and detoxification pathways in both humans and animals.
- Detoxification occurs through enzymatic biotransformation in host cells and in the digestive microbial flora.
- Some of the toxins or their metabolites may bind to animal or human tissues. However, most are excreted in urine, feces, and milk.
- In animals, toxicity is generally revealed as minor chronic issues and rarely causes death.
- The presence of mycotoxins in feed can decrease feed intake and affect animal performance.
- Furthermore, the possible presence of toxic residues in edible animal products (milk, meat, offal) can have some detrimental effects on human health.
- International authorities have established maximum acceptable levels in food and milk for certain mycotoxins.
- The potential risks of mycotoxins can be controlled by verifying plant material for fungal contamination, improving cultivation, harvesting, and storage methods, removing or diluting toxins from contaminated food or feed, and using adsorbents to reduce toxin bioavailability in the animal’s’ digestive tract.