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Dealing with wild yeasts in dairy feeds

July 15, 2019

by Kai Yuan, Ph.D Senior Research and Technical Advisor

Among the reasons that contribute to low milk and milk fat production, the quality of corn silage and high moisture corn is oftentimes a common concern. In non-optimal fermentation or bunk management conditions, various opportunistic wild yeast species can grow rapidly. Well-preserved feed will normally have yeast counts less than 10,000 cfu/g. Under optimum conditions, yeasts can double in number in about 2 h. High yeast counts are indicative of feeds likely to be unstable in an aerobic environment.

Impaired rumen fermentation

Wild yeast reduces nutrient availability of affected feeds and impairs rumen microbial fermentation. Wild yeast, molds, and undesirable bacteria in the feeds can interfere with the populations and activities of normal rumen microbiota and reduce fermentation. Decreased rumen microbial activity reduces the energy and microbial protein available to support milk and milk components. Also, TMR microbial stability concerns can magnify stress conditions for high producing cows with suppressed immune systems.


The mechanism of aerobic instability

Crops with a high concentration of starch will have a tendency to have more yeasts. Thus, high moisture corn and corn silage can be very prone to spoilage when conditions are right. The process is as follows: high yeast populations are ensiled; at feedout yeasts are re-exposed to oxygen and yeast growth becomes exponential; lactic acid is consumed and heating occurs; silage nutrients losses and silage pH rises; higher pH promotes molds and bacteria growth.


The keys to making quality silage

Rapidly exclude air from the forage mass, to begin production of lactic acid and reduction in silage pH, and to prevent the penetration of air into the silage mass during storage. Excessive air, due to slow silo filling or poor packing allows the plant to respire for prolonged periods of time. Air also encourages the growth of undesirable microbes such as yeasts and molds.


Silage management

The silage surface should be smooth to minimize the surface area of the pile exposed to oxygen. Oxygen can penetrate the silage face up to 2 feet during feedout, removal rates are seldom great enough to stay ahead of exponential yeast growth. Remove 6 to 12 inches per day or more in cold weather months, and 12 to 18 inches per day or more in warm months. Minimize the time between feeds removal and feeding. Do not pile aerobically unstable silage or high moisture corn for later feeding, not even for short periods of time.


Minimizing TMR spoilage

If yeast issues persist through silage harvest, ensiling, and feeding management, preservatives based on buffered acids (propionic acids, acetic acids, etc.) can be added directly to TMR to improve aerobic stability.  Buffered mixed organic acid preservatives provide safe, effective control of molds and yeasts.  Since individual organic acids differ in their target microorganisms, use of a mixed organic acid preservative may provide greater, broad-spectrum control than singular acid preservatives. QLF’s Dairy TMR Protector Program offers Myco CURB and Ultra CURB (Kemin Industries) for delivery through QLF products. Delivering TMR preservative through a molasses-based liquid feed provides a convenient, palatable method to safely deliver and distribute preservative in the TMR.


The degree to which silages or high moisture corn are unstable in the silo and ambient temperatures will determine the doses required to stop further spoilage in the TMR. In order to achieve better distribution in TMR and convenience of use, it is recommended to provide acid treatments through QLF liquid feeds. Despite that TMR preservatives add cost to rations, recovery of milk and milk fat production and reduced feed nutrient losses can outweigh the investment.


Lab analysis of yeast counts

Feed can be sent to a laboratory for analyses of yeasts and molds. Samples for microbial analyses should be kept refrigerated (not frozen) depleted of air and sent to the lab as quickly as possible preferably stored with ice packs. This will minimize the growth of yeasts and molds that could grow during transit and thus give a false reading.



In short, aerobically unstable corn silage and high moisture corn oftentimes contain large populations of wild yeast. These species impair feed quality, rumen fermentation, and milk components. Proper silage bunk management and TMR treatments can minimize the harms caused by these undesirable species. Adding TMR preservative through QLF’s TMR Protector Program provides a palatable, safe, convenient, and effective method to deliver and distribute preservative in TMR.



Limin Kung Jr. Aerobic stability of silage. Proceedings, 2010 California Alfalfa & Forage Symposium and Corn/Cereal Silage Conference, Visalia, CA, 1-2 December, 2010.

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