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

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 a reduction in 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 three of an ongoing series covering some of the most important mycotoxins in our agronomic systems.

Fumonisins 

Fumonisins are a group of mycotoxins frequently detected in corn, corn by-products, and other cereals like wheat, barley, oat, and sorghum. Fumonisins are heat stable, meaning standard food-processing methods do not destroy them; therefore, these toxins will be transferred to products manufactured with contaminated raw grain. Among cereals, corn tends to have the highest fumonisin concentrations (2), and it will be the focus of this article.

Fumonisins vary according to their chemical structure, with fumonisins B1 (FB1) being the predominant and most toxic type, followed by fumonisin B2 (FB2) and fumonisin B3 (1). Animal response to consumption of fumonisins varies according to the species, including cancer-promoting activity in rodents, leukoencephalomalacia (fatal brain damage) in horses, pulmonary edema in swine, and liver and kidney toxicity in many species. These conditions can lead to animal death and reduce animal productivity. 

The International Agency for Research on Cancer classifies FB1 as possibly carcinogenic to humans. In humans, fumonisin ingestion may lead to esophageal cancer and liver and kidney diseases. Exposure to fumonisins during pregnancy increases the risk of certain congenital disabilities. Human exposure to fumonisins is greater in countries where staple foods include maize and maize products. 

How does the contamination occur?

Although several fungal species produce fumonisins, the primary producers are Fusarium verticillioides and Fusarium proliferatum, pathogens that cause Fusarium ear and kernel rot of corn in the United States and worldwide. Signs and symptoms of Fusarium ear rot include a white to pink or salmon-colored mold occurring in randomly distributed kernels or clusters (Figure 1). Kernels may present a tan-brown discoloration (Figure 1) and white streaks in a star pattern (starburst) (Figure 2).

Figure 1. Corn ear affected by Fusarium ear rot. Clustered kernels show white fungal growth (middle) and brown discoloration toward the tip. James Stack, Kansas State University, Bugwood.org

Figure 2. Fusarium kernel rot. Photo credit: Alison Robertson, Bugwood.org

Fumonisin-producing fungi survive in corn residue. Fusarium ear rot occurs when spores produced on the crop residue reach the silks through splashing rain and wind and infect developing kernels; or when the fungus enters the plant through roots. Wounds made by insects (European corn borer, earworms, corn rootworm beetles, etc.) or wildlife contribute to dispersal and provide critical ports of entry for the fungus into the ear. Conditions that favor the disease are hot and dry weather during and after silk emergence (3) and when severe damage to the ears has occurred due to insect or hail damage. Furthermore, the risk of fumonisin contamination increases when wet and warm weather conditions prevail before harvest (4). It is important to note that corn ear infection and fumonisin contamination may occur without causing symptoms; therefore, even when ear rot severity appears low, fumonisin concentration in the grain can be high (4).

Disease Management

Contamination with fumonisins occurs while crops are in the field and may continue to increase if storage conditions are suboptimal and favor fungal growth. Choose hybrids well adapted to local conditions and with insect resistance traits. Scout field at R6 to determine disease incidence and severity. If ear rot severity is high, affected fields should be harvested first and handled separately. Drying grain below 15% moisture will prevent further fungal growth and fumonisin contamination, however, fumonisins will remain in the kernels even when fungal growth has ceased. 

Fumonisin Regulations

The Food and Drug Administration (FDA) published guidance for industry with recommended maximum levels of fumonisins.  The recommended limits for corn products intended for human consumption range from 2 to 4 ppm (parts per million or mg/kg). The recommended levels for corn in animal feeds vary according to the species, including equids, rabbits, swine, fish, ruminants, poultry, other livestock, and pets. For the most sensitive species like equids and rabbits, the maximum recommended limit is 5 ppm, while the maximum recommended level is 100 ppm for poultry being raised for slaughter and when the corn product does not account for more than 50% of the diet (on a dry weight basis). Consult with a veterinarian or an animal nutritionist if your corn grain or silage feed is contaminated with fumonisins. 

References

1. Schamale, D.G., and G.P. Munkvold. Mycotoxins in Crops: A Threat to Human and Domestic Animal Health
2. Chen, J. et al. (2021). Research progress on fumonisin B1 contamination and toxicity: A review. Molecules, 26:5238.
3. Crop Protection Network (2022). Fusarium Ear Rot of Corn
4. Crop Protection Network (2016). Corn Disease Management – Ear Rots. CPN-2001

This website, including its text, graphics, and images, is for educational purposes only; 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