Mycotoxins in silage corn: Status and lessons learned
MSU Extension
5 min read
Ear rot damage in silage corn (Huron 2021). White and pink mold are caused by fusarium graminearum and giberrella zeae. Green mold is a result of penicillium.
Mycotoxins in corn grain have been studied and measured for years, but the presence of mycotoxins in silage corn largely has been ignored. Yet the impact of mycotoxins on cattle will be from the total mycotoxin load in the ration, not only from one component.
Many dairy rations rely heavily on silage corn, so quality issues in this important feed are magnified in production aspects.
Fungi such as aspergillus, fusarium, penicillium and gibberella in corn cause accumulation of mycotoxins (toxic secondary metabolites) in corn ear and stalk. Cool, wet weather conditions around silking of corn tends to be favorable for growth of fusarium graminearum and may cause high deoxynivalenol (DON or vomitoxin) accumulation. Feeding by animals and ear-damaging insects such as western bean cutworm and European corn borer provide easy entry for the fungus and intensifies infections. Increased flight of these insects and the failure of cry1F (a type of Bt protein) against WBC have aggravated ear injury and increased infection.
Mycotoxins result in metabolic disruptions in livestock that eat contaminated feed, hence putting their lives and productivity at risk. Some toxins, especially DON, zearalenone (ZON) and fumonisins cause feed rejections leading to loss in milk production, hormonal imbalance, reduced reproductive performance and in some cases animal death.
Mycotoxins can have serious economic consequences for a farm if present in sufficient concentrations. But mycotoxins do not occur in isolation. Often, mycotoxins co-exist and their impact on the health of livestock may be synergistic. That makes it difficult to determine safe levels for individual mycotoxins.
To understand the extent of mycotoxins in Michigan silage corn, the Michigan State University cropping system agronomy lab initiated a three-year survey of Michigan silage corn in 2019. A total of 122 samples from across 22 counties were collected during harvesting seasons of 2019, 2020 and 2021 and analyzed for 26 mycotoxins. The weather conditions at silking in 2019 and 2021 were wetter compared to 2020.
Results corroborated the presence of mycotoxins in the state. All samples tested positive for at least one mycotoxin. Deoxynivalenol was found to be positive in all 122 samples. At least 60% (in 2021) and 50% (in 2019) of the samples had DON concentration greater than 1 ppm (threshold limit for dairy cattle), whereas in 2020 only 12% of samples had DON levels greater than 1 ppm. 2021 had highest levels of DON across three years with two samples greater than 10 ppm and three samples greater than 5 ppm.
Other frequently occurring mycotoxins in 2021 were ZON, fumonisins and moniliformin. However, none of these toxins were found at levels greater than their respective threshold limits (2 ppm, 0.1 ppm, and 0.4 ppm, respectively for dairy cattle). In 2020 and 2019, enniatins and beauvericin were the toxins that occurred in 100% of the samples, but concentration was low.
The second most frequently occurring category of mycotoxins in 2020 were fumonisins, with eight samples at a level greater than threshold (2 ppm). Fumonisin levels were greater than 10 ppm in two samples. Zearalenone occurred in significant amounts only in 2019, with three samples greater than 1 ppm.
Co-occurrence of mycotoxins was reported in all the samples. On average, most of the samples tested positive for at least 10 mycotoxins in 2021 with a maximum of 13 in one sample. In 2020, four samples tested positive for more than 20 mycotoxins and each sample tested positive for at least seven different mycotoxins. Mycotoxin co-occurrence was most pronounced in 2019 of all three years with a maximum of 24 mycotoxins detected in a single sample.
Concentration and frequency of mycotoxins were observed to be dependent on regional weather conditions around silking in corn. In 2020, since growing season was drier and rainfall was more sporadic compared to 2019 and 2021, lower frequency and concentration of mycotoxins was observed. Highest DON and ZON concentration found across tested samples was lower in 2020 (1.4 and 0.07 ppm) compared to 2019 (5.7 and 2.5 ppm) and 2021 (18.4 ppm and 0.23 ppm, respectively). The only toxin that occurred in higher concentration in 2020 than in 2019 and 2021 was fumonisin, with highest concentration of 10.6 ppm in 2020. Fumonisin accumulation occurs due to F. verticilloides infection which is favored when the environment is warm and dry around silking whereas DON is the dominant toxin under cool and humid conditions.
Samples collected from the thumb area (Huron and Sanilac counties) consistently had the highest mycotoxin levels. This probably was due to cool, humid weather, and consistently higher WBC flights in the area which may have contributed to ear wounds. Therefore, more ear rot infections, and eventually higher mycotoxin accumulation.
The question producers ask is, “What should I do with this information?”
Although all samples tested positive for multiple mycotoxins, levels of individual toxins were not above threshold levels in all cases. Beyond that, some of the tested mycotoxins do not have established threshold levels or they might be lower due to synergistic negative impacts of mycotoxin co-occurrence. So, mycotoxin levels must be taken into consideration when making management decisions to prevent risk to livestock health.
Since there are few ways to overcome mycotoxins once they are present in corn, prevention of mycotoxin accumulation in the field using integrated pest management approach is essential. These include hybrid selection, timely planting, fungicide application, scouting and spraying for ear feeding insects, and timely harvest. Recent research at MSU has shown that hybrid selection (use of ear-feeding insect protection trait) reduced insect feeding (70-85%), ear rot infection (70-75%) and eventually mycotoxin accumulations in silage corn at locations with high insect pressure.
Hybrids with resistance against stalk rot (in addition to ear rot) can alleviate accumulation of mycotoxins. RA significant amount of mycotoxins in silage corn may be contributed by stalk rot. Fermentation processes in bunker silos will not break down mycotoxins from an already infected silage corn, making field management even more crucial.
