The 2025 growing season caused many challenges, which are continuing to rear their ugly heads as we try to feed this corn silage and high-moisture corn.
A few areas experienced mycotoxin challenges due to high humidity, while many others were stressed by late-season drought and drier corn silage, which is causing wild yeast challenges.
This winter, we received several inquiries from farms whose cows did not produce as much milk as expected on paper. Many of these farms reported loose manure, decreased milk fat test, lowered intakes and decreased milk production.
Analyzing the numbers
When corn silage samples were submitted for laboratory analysis for mycotoxins, molds and yeast, the yeast counts were very high, at 50 to over 300 million cfu/g. On most of these farms, mycotoxin levels were low, but a few farms also had high mold counts. Wild yeast levels in clean, well-managed silage can be as low as 10,000 cfu/g. Under most conditions, cows can handle TMR levels up to 500,000 cfu/g without adverse effects.
If wild yeast levels were borderline in the winter, a problem that hadn’t emerged yet will show up as days and nights warm up. Wild yeast silage will heat rapidly after exposure to oxygen, leading to a decrease in daily intake. When wild yeast problems develop, activity monitoring systems often see a trend of decreased eating and rumination time; however, this can be a slowly emerging trend in the spring that doesn’t trigger a system alert but can be identified through careful analysis. Wild yeast reduces overall feed intake, disrupts rumen fermentation, lowering bacterial acid production. This will increase starch passage into the hindgut, leading to energy loss and erratic manure consistency.
Testing
Testing for wild yeast can be challenging, as yeast can multiply rapidly during transportation to the lab. Wild-yeast diagnostics often combine on-farm and laboratory testing. For on-farm diagnostics, take samples of all your wet feeds and the mixed TMR, expose them to oxygen for three to four hours, then use a thermometer and your senses to evaluate them. Wild yeast will raise silage temperature above ambient in under four hours.
Also, smell each feed as the wild yeast multiplies; they will give off an alcohol or fresh yeast smell. Sampling should follow traditional forage sampling protocols, ensuring that samples are taken from freshly defaced bunker silos, from the solid face of silage bags, and from the entire face of a silo.
A sample should initially be a minimum of 4 to 6 pounds, then be well mixed and quartered to obtain 1 to 1.5 pounds for shipment to the lab. Since yeast begins to multiply when exposed to air, samples should be vacuum-sealed, if possible, to remove all oxygen. At the very least, samples should be tightly packed in freezer storage zip lock bags to exclude as much oxygen as possible. Both samples should be refrigerated to slow yeast growth and shipped to the lab that day using the fastest available method. Adding freezer packs to the shipment can also slow yeast multiplication from the time it leaves your farm until it arrives at the lab.
Mitigation
Once wild yeast has been identified in your feed, there are a few strategies to help mitigate its impact. The first step is to improve silage management to minimize oxygen exposure. Both silage bags and bunks should be defaced to maintain a smooth face and minimize oxygen exposure, with at least 12 inches of silage removed each day. Silage should be defaced multiple times per day rather than just once, with at least two batches of feed mixed and delivered to each group each day to reduce oxygen exposure.
If feed is heating, refusals may need to be removed twice per day before new feed is delivered. Monitoring rumen health for sub-acute rumen acidosis is critical, as the wild yeast can depress fiber digestibility. Research has found some relief from wild-yeast challenges when a rumen-specific live yeast product is added to the ration, thereby improving rumen function and fiber digestibility.
The final step in management is adding a TMR-saver product containing buffered propionic acid or other acids that prevent silage heating and spoilage. These products are expensive, and inclusion rates will need to be evaluated on your farm to determine the minimum effective rate; rates often increase as temperature rises.
In future years, wild yeast management will begin in the field with plant health management and excellent harvest management. If wild yeast is present, using a silage inoculant containing Lactobacillus buchneri at 400,000 cfu/g of silage will improve aerobic stability of silage.
