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Molds grow over a temperature range of 50°F – 104°F and a pH range of 4 to 8. Mold spores are in the soil and in plant debris lying ready to infect the growing plant in the field or during storage.
Some molds produce mycotoxins under certain conditions but the presence or absence of mold does not directly indicate the presence or absence of mycotoxins. For example, Fusarium molds have been reported to grow prolifically at 77°F – 86°F without producing much mycotoxin, but at near freezing temperatures they produce large quantities of mycotoxins with minimal mold growth (Joffe, 1986). Molds can be detrimental to animal performance regardless of mycotoxin contamination.
Mold identification can be used to determine which mycotoxins are likely to be present.
Mold species:
See the Table 1 below for information on molds and their associated mycotoxins. See Crop Files 6.05.011 through 6.05.018 for more details on molds and mycotoxins (https://cropfile.hostwiki.io/).
Mold spore counts are reported as “colony forming units per gram” or “CFU/g” (see Table 2). Mold spore counts sometimes may underestimate degree of mold present, especially in feeds that have been ensiled for some weeks. Observe and record relative amounts of mold present.
Clean feeds do not contain detectable levels of mold and yeast. Risks refer primarily to effects of mold per se without regard to possible mycotoxin content.
Depressed digestibility, feed intakes and performance may occur from a high mold content without mycotoxins present. More mold does not equal more toxins. Harmful mycotoxins may be present even when there is little or no obvious mold content.
Corn silage, high-moisture corn, earlage/snaplage
Cool growing season resulting in late harvest. These conditions are unfavorable for bacteria species that are responsible for the fermentation and preservation of ensiled feeds.
Symptoms: Very little research is available on the effects of yeasts on animal performance. The most common result of high yeast counts is unstable silages that heat rapidly and subsequently grow additional mold. These unstable silages result in nutrient losses and can potentially reduce dry matter intakes.
¶ Table 1. Mold Species Producing Toxins |
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| Species | Color | Mycotoxin | Conditions Favoring Production |
| Aspergillus | Yellow-green | Aflatoxin Ochratoxin |
Heat and drought stress preharvest, heat and humidity postharvest |
| Fusarium | White to pinkish-white |
Zearalenone
|
Grows both pre- and postharvest. Excessive moisture during flowering and grain fill of wheat. Cool wet growing season with insect damage. Dry conditions mid-season followed by wet weather. Associated with ear and stalk rot in corn, head scab in small grains, red ear rot, and pink ear rot |
| Penicillium | Green to green-blue | Ochratoxin | Cool, wet, and low pH (acid tolerant) postharvest |
| Cladosporium | Dark blue-green to gray or black | None | Early frost, neutral pH, high grain moisture (30-40%), temperatures at 75-125°F. |
¶ Table 2. Mold Spore Count Interpretation |
|
| CFU/g (air dried) | Feeding Risk and Cautions |
| Under 500,000 | Relatively low count |
| 500,000 to 1 million | Relatively safe |
| 1 to 2 million | Feed with caution Discount energy (x .95) |
| 2 to 3 million | Closely observe animals and performance Discount energy (x .95) |
| 3 to 5 million | Dilute with other feeds Discount energy (x .95) Observe closely |
| Over 5 million | Discontinue feeding |
¶ Table 3. Yeast Count Interpretation |
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| CFU/g | Aerobic Stability | Comments |
| <10,000 | 120-140 hours | Typical values in well preserved feed |
| 1,000,000 | ~ 40 hours | |
| 25,000,000 -50,000,000 | Upper range for inadequately fermented feed. | |
Joffe, A.Z. 1986. “Fusarium Species: Their Biology and Toxicology”. John Wiley and Sons, Inc. New York
Kurtzman, C.P., B.W. Horn, and C.W. Hesseltine. 1987. Aspergillus nomius, a new aflatoxin-producing species related to Aspergillus flavus and Aspergillus tamarii. Anton v. Leeuwenhoek 53:147-158.
Adams, Richard S., Kenneth B. Kephart, Virginia A. Ishler, Lawrence J. Hutchinson, and Gregory W. Roth. "Mold and Mycotoxin Problems in Livestock Feeding." Dairy Cattle Nutrition (Penn State Extension). Penn State Extension, n.d. Web. 17 Sept. 2013.
Hoffman, P., R. Shaver, and P. Esker. 2009. High moisture corn, aerobic stability, feed additives, and mycotoxins: Common questions. The 2009 Wisconsin Corn Corp.
Write, C. B. Holland, R. Daly and L. Osborne. 2009. Moldy corn for beef cattle. SDSU Extension Estra: 2069.
Wilkinson, J. M. and D. R. Davies. 2012. The aerobic stability of silage: key findings and recent developments. Grass and Forage Science. Blackwell Publishing Ltd. doi: 10.1111/j.1365-2494.2012.00891.x.