Fumonisins Molds and Mycotoxins in Corn, Why Should We Care?

Juan Pineiro, Texas A&M AgriLife Extension Dairy Specialist – Amarillo
Jourdan Bell, Texas A&M AgriLife Research and Extension Agronomist – Amarillo
Ed Bynum, Texas A&M AgriLife Extension Entomologist – Amarillo

As the harvest season approaches, concern is raising among crop farmers and dairymen after the unusual hot summer we experienced which would increase plant stress and predispose to ear molds growth. If this combines with delayed harvest, late season rains and cool periods then a concern for mycotoxin production would also arise.

Annual cost of mycotoxin contamination of crops in the US was estimated to be on average $1.4 billons due to crop contamination losses from price discount when selling grain, mitigation costs and livestock production losses. Mycotoxins are frequently present in silages, hay, concentrates and forages fed to livestock. Among mycotoxins of greatest concern to dairy cattle, fumonosins are the most prevalent in livestock feeds, and thus represent a frequent threat to cattle. Fumonisins are mycotoxins produced by Fusarium molds capable of causing disease and death in exposed animals and humans. This article will focus on the effects of fumonisins in humans and animals, and prevention strategies.

So, what are molds and mycotoxins? As you may know that fuzzy and dusty structure in your leftover pasta with tomato sauce that you forgot 1 week in your fridge are known as molds. Molds are fungi that frequently grow in feedstuffs fed to livestock and some of them may cause disease (i.e., mycosis) in different locations such as lungs, mammary gland, or intestine (e.g., hemorrhagic bowel or bloody gut). In addition, molds may produce toxic metabolites called mycotoxins, capable of causing disease (i.e., mycotoxicosis) and death in exposed animals and humans.

Molds are widely distributed in the environment and mold spores are present in soil and plant debris; thus, mycotoxins can be formed in the field, during harvest, storage, or feeding if the conditions are appropriate. Plant stress due to weather extremes, insect damage and inadequate storage or feeding practices predispose to mold growth and mycotoxin production. Feedstuffs contaminated with molds might contain multiple mycotoxins, which confounds the expected effects on cattle. Previous research has shown that mycotoxins provided by a naturally contaminated feed are more toxic than the same level of a pure mycotoxin added to a diet. These results might be explained by the interaction with other unidentified mycotoxins in naturally contaminated feeds. In addition, since molds can produce different type of mycotoxins and different feedstuffs are included in the diet of dairy cattle, several mycotoxin interactions may occur.

There are 5 primary mycotoxins (aflatoxin, fumonisin, ochratoxin, deoxynivalenol –DON– a.k.a. vomitoxin, and zearalenone) that can be present in corn. Of the 5 primary mycotoxins, fumonisin can infest corn under specific environmental conditions and is produced by two Fusarium fungi species (F. verticilloides and F. proliferatum). Fusarium species are found worldwide in soil and crop residues, but not all Fusarium species produce fumonisin. Fusarium can infest other plant parts including the stalk resulting in Fusarium stalk rot, but both starch and specific environmental conditions are necessary for fumonisin to develop in corn kernels. Specifically, early season heat and drought predisposes a plant for Fusarium followed by rain and high humidity during grain development results in fumonisin development as the kernel matures. Several variations of fumonisin (FB1, FB2, FB3, and FB4) can be present in corn, but FB1 is the most prevalent. Visible symptoms of Fusarium ear rots can alert the producer that fumonisin may be present. Visual symptoms include white and salmon colored powdery growth and starburst streaking on the kernel, but the presence of Fusarium ear rot does not guarantee fumonsin development.

Chronic exposure to fumonisins might result in esophageal cancer and neural tubes defects in humans, leukoenchephalomalacia (i.e., softening of the white matter in brain) in equines, pulmonary edema in pigs, and liver and kidney toxicity in all domestic species studied. Dairy cattle are more resistant than monogastrics (e.g., horses, pigs) to mycotoxins because of ruminal mycotoxin degradation. Ruminal degradation of fumonisin in cattle ranges from 60 to 90%. However, dairy cattle may be more susceptible than beef cattle due to greater feed consumption and stress events (e.g., calving). Nevertheless, this would not translate in a public health concern, since the carryover of fumonisin from feedstuffs to milk is negligible. At high concentrations, mycotoxins can cause acute health issues and production losses. However, since ruminal degradation of mycotoxins might protect cows against acute toxicity, usually lower concentration levels of mycotoxins may interact with other stressors to cause poor reproductive performance, higher disease incidence and subclinical losses in performance. These subclinical losses have a greater economical impact than acute health problems, but are more difficult to detect.

How much fumonisin in feedstuffs is safe for dairy cows? Previous research found that dairy cows fed diets containing Fumonisin at 100 parts per million (ppm) from 1 week before to 10 weeks after parturition reduced by 6 kg/d milk production, primarily due to reduced feed intake but probably also due to mild liver toxicity. The US Food and Drug Administration (FDA) regulatory guidance for lactating dairy cattle is 15 ppm of diet DM. In other words, fumonisin should be less than 15 mg/kg of diet DM, or 30 mg/kg of corn DM if fed ?50%, in diets formulated for lactating dairy cows.

What preplant decisions can be made to minimize the risk of fumonisin development? While producers cannot control environmental stress, some pre-season decisions can help producers minimize their risk for Fusarium infection and ultimately fumonisin development. Hybrid selection is one of the most important preplant decision a producer can make. While yield potential is often the deciding factor for hybrid selection, other important characteristics are:

1) Irrigation Capacity and Plant Population: Producers should evaluate their well capacity prior to planting corn. Because irrigation mitigates drought and heat stress, corn grown on low well capacities is often at a greater risk for Fusarium infection. Additionally, producers should also manage plant populations to minimize stress. High populations planted on low water can compound plant stress.

2) Maturity Class: Newer, earlier maturing corn hybrids provide producers the opportunity to potentially save several inches of irrigation; however, it is observed that earlier maturing hybrids often have poor kernel integrity. As the corn pericarp prematurely dries in the field during late grain fill, the kernel splits further predisposing the ear to fungal pathogens.

3) Fusarium Ear Rot Resistance Ratings: Many hybrids are screened for Fusarium resistance, but it is important for producers to inquire with seedsmen about ratings unique to each hybrid.

4) Insect Traits: Above ground Bt traits target worms in corn ears. Damage from corn earworms, fall armyworms, and western bean cutworms is strongly correlated with Fusarium ear rots and fumonisin. So, producers should consider Bt insect traits for managing ear worms and reduce feeding damage to minimize Fusarium development. However, we are beginning to see more unexpected survival and damage with the Bt corn hybrids currently used for our corn ear pests. Producers may want to look at planting corn hybrids with the Bt Vip3A trait. This trait is showing good protection against the three lepidopteran ear pests.

5) Husk Coverage: On the Texas High Plains, few elevators use driers; consequently, it is necessary for corn to air dry in the field until a grain moisture of approximately 14% is reached. Many hybrids grown on the Texas High Plains are open husk hybrids because, the open husk permits the kernels to dry more quickly. However, the ear with an open husk is at a greater risk for bird and insect damage.

6) Ear Orientation: Most of the hybrids currently grown on the Texas High Plains have a short shank, which results in an upright corn ear. An upright ear with an open husk will dry down more quickly under dry conditions, but an upright ear with an open husk will hold water during moist conditions, which magnifies Fusarium ear rot infection and the risk for fumonisin development. While precipitation is responsible for water accumulation in the husk in most fields, poorly placed irrigation nozzles may also result in corn ears being repeatedly hit with water later in the season. Consequently, downward facing ears allow for water to drain away from the ear during the later stages of grain development.

What preharvest decisions can be made to minimize the risk of fumonisin development?

As corn harvest approaches on the Texas High Plains, producers should be evaluating corn fields for visual symptoms of Fusarium ear rots. Specifically, producers should identify potential “hot” areas in their fields. If Fusarium is only present in areas with the greatest stress such as the southwest corner, the producer should consider strategic combining. Rather than mixing contaminated corn into several loads, it may be beneficial for the producer to segregate the clean and moldy areas to minimize risk of contaminating multiple loads from the field. Additionally, the producer may consider adjusting the fan speed to blow out light weight, moldy corn, cob pieces, and fines that are often highly contaminated with fumonisin. In some regions, it is recommended to leave tip kernels attached to the cob because the tip kernels are often at the greatest risk for Fusarium and fumonisin. To leave tip kernels attached to the cob, it is suggested to run the combine at full capacity with the concave settings open and the cylinder speed at a low setting. If the producers suspect high levels of fumonsin present based on visual observations of Fusarium, the producer needs to contact his or her insurance agent prior to harvesting the com.