Mycotoxin Survey in US corn: May 2018 update

Design

For the 2017 corn harvest, a total of 642 samples sourced from 32 states were analyzed in 3 different labs (Romer Labs Inc., USA; Veterinary Diagnostic Laboratory at Iowa State University, USA; Activation Laboratories, Canada) to characterize the presence and potential risk posed to livestock animal production by six major mycotoxin groups: aflatoxins (Afla), zearalenone (ZEN), Type B Trichothecenes (B-Trich), fumonisins (FUM), Type A trichothecenes (A-Trich), and ochratoxin A (OTA). Samples included corn (388, 60%), corn silage and fresh corn chop (189, 29%), and corn byproducts (65, 10%).

Occurrence

A total of 91% of samples tested positive for mycotoxins compared to 96% in 2016. Type B trichothecenes such as deoxynivalenol continue to pose a major threat to livestock this year, with an occurrence at 78%, average contamination level of 1,027 ± 122 ppb (all values are presented as an average ± SEM), and maximum of 54,149 ppb. Both occurrence and average level are decreased for B-Trich compared to 2016 (85% occurrence with an average of 1682 ± 96 ppb, maximum of 30,440). FUM for the current sample pool is less than 2016 with a prevalence of 45%, an average contamination level of 2343 ± 294 ppb, and a maximum of 64,500 ppb. This is compared to 70% and an average of 3878 ± 410 ppb in 2016. However, the current sample pool is skewed towards Midwestern corn, and those in Southern areas should be mindful of FUM contamination of the 2017 crop from corn grown in these regions.

Table 1. Summary of mycotoxin analysis

ParametersB-TrichFUMZENAflaA-TrichOTA
Positive samples (%)7845324<1<1
Mean of positives [ppb]1027234224712114600
SEM1 of positives [ppb]12229436334*NA
Maximum contamination [ppb]54,14964,5005,55667207600

1Standard error of mean

Figure 1. Prevalence (%) and average contamination level (ppb) of positive samples for Afla, ZEN, B Trich, and FUM from 2012 to 2017. OTA and A Trich are not represented due to low number of samples

Prevalence (%) and average contamination level (ppb) of positive samples  

The prevalence of ZEN in the 2017 harvest was 32%, with an average of 247 ± 36 ppb, and maximum of 5556 ppb. Average sample contamination level and prevalence is lower for ZEN compared to 2016 (2016: prevalence at 56% with a mean of 339 ± 62 ppb). Prevalence and average contamination levels of B-Trich, FUM are less than 2016, and appear similar to 2015 while prevalence of ZEN is greater than 2015. Contamination levels of B-Trich and FUM remain above 2015 levels. The overall trend has been increasing prevalence of B-Trich and ZEN contamination since 2013, with a decreasing trend of FUM. Afla prevalence in the sample pool appears to have decreased since 2012, but this year due to weather during the harvest and out-door storage of bumper crop corn, producers should remain vigilant of corn quality and storage conditions throughout the calendar year.

Risk level

Figure 2. Threat of mycotoxin-related risks to livestock based upon threshold levels according to FDA and EU regulatory and guidance values. States from which samples with levels of contamination representing a high risk are illustrated in red. States with positive samples below high threshold levels are illustrated in pink, without positive samples are illustrated in dark grey, and without samples submitted are illustrated in light grey. State information was not available for all samples. The maximum level does not preclude specific, severe instances of mycotoxin contamination in farm or fields locally, nor does it account for the negative impacts of multiple mycotoxin presence. OTA and A-Trich maps are not included due to small number of positive sample

Risk Level

The contamination of samples with B-Trich above 900 ppb and FUM above 2000 ppb was observed in 16 and 19 states, respectively. Zearalenone levels exceeding 100 ppb were detected in samples from 21 states. The occurrence of samples above threshold levels for Afla, T-2 and OTA were sparse, and found in samples from single sources. Samples of Afla above 20 ppb were detected in South Carolina and Alabama, A-Trich at levels above 100 ppb was found in New York, and OTA above 100 ppb was found in Ohio.

Distribution

Figure 3. Distribution of contaminated samples

Distribution

Detected occurrence above the risk level of 100 ppb was 62% for ZEN (73% in 2016) while it was 29% for B-Trich above 900 ppb (51% in 2016), and 28% for FUM above 2,000 ppb (42% in 2016). This 2017 harvest, B-Trich, ZEN, and FUM present the main threats in the US corn, consistent with previous years.

Co-occurrence

With more than ten-years of experience monitoring the occurrence of mycotoxins in livestock feeds, BIOMIN has shown that co-occurrence of mycotoxins (the presence of more than one mycotoxin) is the rule and not the exception. As illustrated in Figure 4, 43% of US corn samples harvested in 2017 were contaminated with just one mycotoxin while 48% showed co-contamination with more than one mycotoxin, a decrease from 2016 and similar to 2015. Of the co-contaminated samples, 18% were positive for all three fusarium toxins (B-Trich, FUM, and ZEN), while co-contamination with B-Trich and FUM, and B-Trich and ZEN were 14% and 13%, respectively.

Figure 4. Co-occurrence of mycotoxins from 2012-2017.

Co-occurrence of mycotoxins from 2012-2017.

Summary

Overall, B-Trich such as deoxynivalenol present the highest threat in the US corn harvest samples due to its high prevalence and number of samples above the FDA recommended level.

In terms of occurrence, FUM ranks second among the six major mycotoxins analyzed in these samples.

As a result of its co-occurrence with other toxins, ZEN continues to be a concern in US corn.

While occurrence and co-occurrence levels in 2017 have decreased compared to 2016, data suggests fusarium toxins in combination remain a threat to the livestock industry.

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