Growing Beef Newsletter
October 2026, Volume 17, Issue 4
Wet Fall Weather and Feed Quality
Garland Dahlke, Iowa Beef Center research scientist
It is a gross understatement to say wet harvest conditions have made it a challenge to make high quality feed. Starting with the moisture aspect, wet field conditions tend to encourage mud/soil contamination into the feed and this tends to be elevated further on a drive-over packed pile of silage. Along with any mud that flies into the wagon, contaminated tires provide an effective way to inoculate the entire pile with undesirable micro-organisms from the soil. The Clostridium spp, which we would routinely try and avoid through vaccinations, are soil dwellers and can set up a home in silage as well as Listeria, E. coli and Salmonella spp. - this list goes on. A good pack that excludes oxygen and has a rapid drop in pH will certainly help prevent trouble, but in a wet harvest season scenario, the breaks in harvest can make it more difficult to achieve this. Feed testing labs can provide a “Feed Hygiene” test to allow some of these unwanted contaminants to be identified and further testing can be done to identify the “bioamines” that might result. The problem though, is that the silage is already contaminated and there really is no way to fix it once it is messed up. Often this contaminated silage becomes a problem the following spring when weather warms up and the microbial growth resumes. For example, it is not uncommon to see outbreaks of listeriosis in spring because of this resumed growth.
What to do? First - try not to make it worse. Then pack and cover. It is really difficult to know when enough packing density is reached, but after spending some time with a Dickey John soil probe with a ¾ inch tip I have found that a sustained pressure greater than 100 pounds per square inch for a depth of 18 inches generally seems to be a good minimum for silage. The drier the silage gets because of a delayed harvest, the harder it can be to pack and get a rapid fermentation so it may take some amendment to assist in the fermentation process such as added water, syrup from an ethanol plant or liquid molasses.
Moving on to other unwanted microbial tenants. Molds and yeasts are part of the territory as well. Both of these groups of organisms tend to prefer higher pH levels and need a little bit of oxygen to live, thus keeping the air out of the pile is important here as well. However, in wet climates many of these organisms have already done a fair amount of damage in the field prior to harvest. Yeasts are interesting in that some are good and some are bad. During my time as a feed rep in Wisconsin, the strategy to deal with high yeast counts in feed was to add more yeast only from a domesticated strain like brewers yeast to combat the problem and it seemed to work. Some of the wild, undesirable yeasts tend to reduce the palatability of the feed and probably cause other issues if we start looking into the matter more thoroughly.
Fusarium molds thrive in wet field conditions and are pretty common. Often you will see traces of this mold on the plant appearing in red streaks, but also could be pink, purple, salmon or white in color. The mold tends to go away if there is no air or if the pH is low, however the toxins they produce will be left behind regardless if oxygen is excluded or the pH drops as it should. Deoxynivalenol (DON or vomitoxin) and Zearalenone are common mycotoxins produced by this mold and may be used as indicators that other toxins could be present. Other toxins like T2 also appear in wet conditions often on fields where manure was applied and not worked into soil prior to planting and there are more. Over 400 mycotoxins have been documented, but not all like wet conditions. For instance, aflatoxin is more likely to be found in droughty conditions. It should be noted that just because a mold is present, it does not mean that a mycotoxin has been produced. Also, as somewhat implied, much of the mycotoxin issues occur out in the field prior to storage. However careless storage can add to the problem since some of the fusarium molds, for instance, continue to produce more toxins in storage if left unchecked. Cold weather would keep the micro-organisms from growing and making a bigger problem, but the mycotoxin is already there and will be a problem regardless of the weather or storage conditions.
To deal with these, there are a few feed additives that might be effective, however each toxin requires a different binder, treatment, enzyme or organism to render it harmless. No easy prescription here. There is one thing we can do that does seem to help a little in all cases if a mycotoxin is detected in higher levels and that would be to remove the ionophore, if used, from the diet. One target of the ionophore is rumen protozoa. These organisms tend to steal nutrients from the animal and therefore we would normally add an ionophore to keep their effect to a minimum. In the case where there is a mycotoxin present though, the presence of protozoa is beneficial since they have been shown to metabolize mycotoxins and are a natural defense against mycotoxins.
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