Current Progressive Dairy digital edition

Wild yeasts: A perennial problem

Tony Hall and Renato Schmidt for Progressive Dairy Published on 01 October 2020
Feed wagon

How to mitigate and prevent spoiled silage for the future

Throughout the summer, many dairy consultants have seen farm teams challenged by aerobically unstable 2019 ensiled forages and high-moisture grains, which were grown under several levels of stress.



Higher ambient temperatures caused an exponential increase in wild yeast growth and activity – in both the farm-grown ensiled feeds and the total mixed ration (TMR) in which they are incorporated. The net result has been unstable, hot feed in front of cows which has been contaminated with high, rapidly multiplying populations of wild yeast (some species can double their population within two hours) and silage robbed of its most digestible components. This, in turn, has led to a less palatable ration with poorer nutrient value and challenges to digestion, leading to drops in milk and milk component yield.

2019 and beyond

Wild yeasts are opportunistic microorganisms that are always present on silage crops. The wild yeast population on plants in the field typically ranges from 1,000 to 1 million colony-forming units (CFU) per gram of forage, on an as-fed basis. They are prevalent on both high-starch and high-sugar crops such as high-moisture grains, corn silage and even higher dry matter haylages. Wild yeasts are responsible for starting the process of aerobic instability, as they break down lactic acid that is so desirable in the fermentation process, which immediately emphasizes the need for very good silage-making and feedout practices, as well as adding a specific microbial inoculant that helps inhibit wild yeasts.

Many crops experienced stressful field growing conditions: excessive moisture, delayed or very cool harvest conditions, and some regions had a combination of both. These are the types of ensiling conditions that can make it easy for wild yeast populations to survive and be ready to thrive at feedout. Experience actually informs all of us that there is no “perfect” season or year for “easy” silage making – as a matter of fact, the recent years have shown otherwise. In reality, the villainous wild yeasts are rampant and a perennial threat waiting to multiply and disrupt herd production. For crops awaiting harvest and ensiling, it’s a matter of prevention.

Silage management practices to prevent excess wild yeasts on crops

  • Weather permitting, harvest the crop at the optimal stage of maturity and dry matter content and for the method of storage (bunk, pile, tower or bag).

  • Magnify the value of your silage with an effective research-proven forage inoculant with a strain-specific homolactic bacteria and Lactobacillus buchneri combination. Silage researchers back up efficacy claims when L. buchneri is applied at 400,000 CFU per gram crop. Four to six weeks after ensiling, the L. buchneri will generate acetic acid, which contains potent anti-fungal properties.

  • Harvest in a timely manner; avoid delays or interruptions in field work and at the bunk or pile. Any delay exposes the crop to oxygen and allows some unwanted wild yeast metabolism and growth.

  • Effective packing is crucial and cannot be overlooked. Proper packing requires thin crop layers (6-inch maximum) and the tractor numbers and combined weight to match the frequency and weight of the crop delivery to the storage structure (free tools can be found here: Forage inventory).

  • Seal quickly and effectively. Any delay in sealing continues exposure to oxygen and risks stimulating the wild yeasts.

  • Be safe. While the process is best done quickly, don’t skimp on safety measures. Outfit your silage-making teams with high-visibility safety jackets as well as being vigilant of personnel around machinery and storage structures.

Overall, these recommendations should not be a surprise; they are part of good silage management. Don’t give wild yeasts the opportunity to rob your forages of their ability to support your cows’ nutritional needs.

Mitigating wild yeast in the current feed program

Even on well-managed silage faces, oxygen can penetrate up to 4 feet into the bunker or pile. It can be hard to get ahead of heating or spoiling feed. There are many potential ways to help mitigate the negative effects of high wild yeast populations in ensiled feeds. It takes effort and extra spending, so a lot depends on what the farm team can, or will, invest in. As corrective actions are evaluated, these thought-starters are pertinent:


  • Can this wild yeast-contaminated forage be used only in the winter?

  • Can the contaminated silage at least be diluted out in the ration?

  • Can the farm team remove up to 12 to 18 inches deep for use across all the rations?

  • Is it possible to keep the face smooth with a defacer or another good shaving technique?

  • Can the feeding team minimize the use of drop piles and mix into a TMR immediately?

  • Is it possible to ensure TMR refusals are cleaned away from the feedbunk before a fresh load of TMR is delivered?

  • Can the TMR be mixed and fed twice daily instead of once?

  • Can sub-acute ruminal acidosis (SARA) be avoided? A wild yeast-contaminated TMR tends to depress ration fiber (NDF) digestibility and may predispose cows to SARA. Research supports including a rumen-specific active dry yeast probiotic to the ration which improves rumen function and fiber digestibility.

  • Can a “TMR-saver” product be mixed in the ration to try and keep the feed stable longer? This is usually a product based primarily on buffered propionic acid (65% propionic acid is common), sometimes with other acids included. “TMR-savers” are not affordable over the long term when applied at the recommended rate, which starts at 6 pounds per ton of TMR as fed. Use this for five days to see if the TMR becomes cool and stable. If it seems to be working, take the inclusion rate down slowly to a level that keeps the TMR stable for the lowest input cost (usually around 4 pounds of “TMR-saver” per ton of TMR as fed).

Wild yeast contamination is expensive

Once ensiled crops become heavily contaminated with wild yeasts, it becomes both resource-constraining and expensive to deal with them. However, not addressing the problem is expensive in terms of lost nutrient value and palatability in the silages and high-moisture grains, unstable TMR, expensive acid-based preservative inclusions and variable cow production.

Even moderate heating due to wild yeasts can rob your herd of $36 per cow annually. It is much more economical to commit to an effective silage-making program that includes a trusted and research-proven forage inoculant that puts you in control of your silage fermentation, enhances feed digestibility and feedout stability and helps maximize profitability. end mark

PHOTO: When wild yeasts are present, immediately adding feed to the TMR is preferred to using drop piles. Photo courtesy of Lallemand Animal Nutrition.

Tony Hall received his master’s in animal science from Aberdeen University in Scotland and is employed by Lallemand Animal Nutrition, North America as a technical services – ruminant team member.

Renato Schmidt received his Ph.D. in animal nutrition from the University of Delaware and is employed by Lallemand Animal Nutrition, North America as a technical services – forage team member.

Tony Hall
  • Tony Hall

  • Technical Services – Ruminant
  • Lallemand Animal Nutrition, North America
  • Email Tony Hall