From Aflatoxin to Zearalenone: Key Mycotoxins You Should Know – Zearalenone

Mycotoxins are substances produced by fungi that infect grain crops like maize and small grains and cause ear and kernel rots. Exposure to mycotoxins can lead to chronic or acute toxicity in humans and animals. In addition, mycotoxins can lead to market losses, discounts, rejection of grain lots at elevators, and reduced livestock efficiency and productivity.

The most economically important mycotoxins include aflatoxins, deoxynivalenol (DON, also known as vomitoxin), fumonisins, ochratoxin A, T2, HT-2, zearalenone, ergot alkaloids, and patulin. The fungal species that produce mycotoxins have worldwide distribution; therefore, mycotoxin contamination occurs everywhere grain crops are grown. Accordingly, mycotoxins have been detected in feed, silage, food, and beverages derived from cereal grains and animal products exposed to contaminated feed.

This is part four of an ongoing series covering some of the most important mycotoxins in our agronomic systems.

What is zearalenone and where does it occur?

Zearalenone (ZEN) is a mycotoxin produced by several Fusarium sp., predominantly Fusarium graminearum and Fusarium culmorum. Common diseases caused by these species include Gibberella ear rot in corn (Figure 1), and Fusarium head blight in wheat (Figure 2) and other grain crops.  ZEN can often co-occur with the mycotoxin deoxynivalenol (DON), as these species are also major DON producers. Zearalenone gets its name for its occurrence in corn; Zea mays “zea”, and its chemical structure; resorcylic acid lactone “ral”, “en” for presence of a double bond, and “one” for ketone group (1). While ZEN was first detected in corn, it can occur in other cereal grains, including wheat, barley, sorghum, oat, hay and silage. In corn, the production of ZEN by F. graminearum is often favored by moderate temperatures and high humidity (2).

Figure 1. Gibberella ear rot of corn (Photo credit: Adriana Murillo-Williams, Penn State)

Figure 2. Symptoms and signs of Fusarium Head Blight in wheat (Photo credit: Adriana Murillo-Williams, Penn State)

Chemical structure

ZEN is a non-steroidal estrogenic mycotoxin, similar in structure to naturally occurring estrogens. ZEN can also occur in derivatized forms such as α-Zearalenol (α-ZEL), β-zearalenol (β-ZEL), α-zearalanol (α-ZAL), β- zearalanol (B-ZAL), and zearalanone (ZAN). Being an estrogenic compound, ZEN’s toxicity is often associated with its affinity to estrogenic receptors, mainly in farm animals. The derivatized forms also have estrogenic effects, however, they vary in the magnitude of estrogenic activity compared to ZEN (2,3).

While acute levels of ZEN are not often problematic, high levels or prolonged exposure to low levels can cause reproductive problems in animals. By binding to estrogen receptors, ZEN can amplify the natural processes governed by estrogen activity.

The animal species most sensitive to ZEN are swine and ruminants, while the most resistant are birds, like chicken and poultry. Swine are particularly sensitive, with as little as 1-5 ppm causing estrogenic effects (4). In females, ZEN can cause reduced fertility, reproductive disorders, and developmental problems in reproductive organs. In males, ZEN can also lead to disorders in reproductive development, including testicular atrophy and enlargement of mammary glands (1).

Disease management

The majority of ZEN contamination occurs during infection while the crop is growing in the field. However, ZEN production can proliferate if grain is stored under poor, high-moisture conditions. Management practices aimed at prevention are recommended, as managing grain that is already contaminated can be difficult. Many Fusarium sp. which produce ZEN can infect both corn and cereal grains, therefore, continuous corn can increase mycotoxin risk and should be avoided. Including non-hosts, like soybean or alfalfa, in your rotation can reduce the presence of inoculum in the field. Additionally, inoculum can overwinter in residues like corn and wheat stubble. Therefore you may consider managing residue if infection was severe in the previous season.

Fusarium spores can also travel long distances aerially, therefore, reducing in-field inoculum is not the only solution. Corn and wheat varieties which offer genetic resistance to diseases like Gibberella ear rot and Fusarium head blight (FHB) can limit mycotoxin contamination. Fungicides like those in the triazole group may be applied to reduce FHB in wheat, but offer limited protection in corn. Even with all these management practices, ZEN contamination may still occur, therefore it is important to store grain at 15% or less to reduce proliferation during storage, and monitor disease in the field, harvesting diseased sections separately.

Zearalenone regulations

Currently, the FDA has not established guidance levels for ZEN contamination in grain or food products. However, the WHO/FAO determined the lowest observed adverse effect level (LOAEL) of ZEN at 200 g/kg bw/day for pigs and gilts, 17.6 g/kg bw/day for piglets, 56 g/kg bw/day for sheep, and 20 g/kg bw/day for dogs. The LOAEL describes the lowest tested dose of a toxin that has been reported to cause adverse health effects.

For livestock farmers, it is important to understand the symptoms of ZEN toxicoses, so that grain can be tested if estrogenic disorders are observed. If corn ear rot or Fusarium head blight symptoms are observed in the field or in storage, it may be useful to test for ZEN, especially if grain is to be fed to sensitive livestock like swine.

The content of this article is for educational purposes only, and it is not intended to be a substitute for veterinary medical advice, diagnosis, or treatment. Always seek the advice of a licensed Doctor of Veterinary Medicine or other licensed or certified veterinary medical professional with any questions you may have regarding a veterinary medical condition or symptom.

References:

1. Ropejko, K. & Twarużek, M. (2021) Zearalenone and Its Metabolites—General Overview, Occurrence, and Toxicity. Toxins vol. 13.
2. Mahato, D. K. et al. (2021) Occurrence, impact on agriculture, human health, and management strategies of zearalenone in food and feed: A review. Toxins vol. 13.
3. Shier, W. T., Shier, A. C., Xie, W. & Mirocha, C. J. (2001) Structure-activity relationships for human estrogenic activity in zearalenone mycotoxins. Toxicon vol 39(9).
4. Woloshuk, C. & Wise, K. Diseases of Corn: Gibberella Ear Rot. Purdue Extension BP-77-W.