Poor animal performance has been associated with high concentrations of yeasts which typically occur when the feedstuff was exposed to an environment with excess air due to improper or insufficient ensiling. A study was recently performed to determine if commonly found yeast associated with this spoilage (which had been isolated from the silage) could potentially alter rumen fermentation processes inside an environment similar to the rumen.

One colony of Issatchenkia orientalis was isolated from high moisture corn and grown in an appropriate medium. After the yeast culture was purified to ensure accurate results it was added to culture tubes which each contained a total mixed ration of 43% concentrate, 43% corn silage, 11% alfalfa haylage and 3% alfalfa hay (dry matter basis) as well as a buffer and ruminal fluid to achieve several final concentrations.

The following final concentrations researchers predicted to achieve included 0 (CTR), 4.40 (low yeast, LY), 6.40 (medium yeast; MY) and 8.40 (high yeast, HY) log10 cfu of yeast/mL. Each aforementioned treatment was studied in seven test tubes and incubated for 12 and 24 hours at 39°C (102.2°F). Once the incubation period concluded researchers analyzed samples for volatile fatty acids (VFA), fatty acids (FA), pH, yeast number, and neutral detergent fiber (NDF) digestibility.

When analyzing samples it was found that over time all viable yeast counts decreased. However, yeast counts were still highest after conclusion of the 24 hour incubation period for HY yeast and also indicated a lower pH, higher concentration of total VFA in the culture’s fluid and decreased NDF digestibility when compared to other treatments. MY also showed decreased NDF digestibility but not to the same degree as HY.

When comparing all samples the biohydrogenation (addition of a Hydrogen molecule to a saturated fat to create an unsaturated fat) was not affected by adding I. orientalis and actually did decrease over the time period as saturated FA’s accumulated. Saturated FA’s with the most prevalence included palmitic acid and stearic acids. In conclusion I. orientalis (especially at high levels) can certainly alter any aspect of ruminal fermentations and decrease NDF digestibility.

Link to abstract Effects of a spoilage yeast from silage on in vitro ruminal fermentation

Author: L. Kung Jr. Department of Animal and Food Sciences, University of Delaware lksilage@udel.edu