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A new tool to measure yeast efficacy in dairy cows

November 23, 2021
Digestive efficiency in dairy cows

Yeast supplementation is a common practice to improve the efficiency of feed utilization and performance in dairy cows. It is well-known that supplements containing live yeast can improve rumen fermentation and the digestive process by stabilizing rumen pH and stimulating the growth of beneficial microbial populations. These positive changes can be attributed to growth factors, including peptides, and the effect on the rumen anaerobiosis to create optimal conditions for the rumen microflora.

Good rumen function will ensure optimal feed intake and digestive efficiency in dairy cows, while poor rumen function can negatively impact feed intake, health and overall cow performance. Formulating the ration correctly and understanding how the individual ingredients in the ration work together can help keep the dairy cow’s rumen and digestive system functioning properly.

How can you ensure that good formulations will lead to the expected results?

Published research and decades of use in the field suggest that most dairy diets respond positively to Yea-Sacc®, a yeast culture based on Saccharomyces cerevisiae that stimulates the growth of fiber-digesting and lactic acid-utilizing bacteria in the rumen. These microbial changes directly result in:

  • A stable rumen pH, which is conducive to better fiber digestion and a reduced risk of rumen acidosis
  • Improved feed intake
  • Enhanced milk yield and components

However, not all formulation strategies react the same way. As a result, there may be instances in which supplementation with Yea-Sacc does not yield the expected results.

To quantify the efficacy of Yea-Sacc for improving rumen fermentation and nutrient utilization for specific dairy TMRs, allowing for greater precision when feeding Yea-Sacc, Alltech created the Alltech IFM™: Yea-Sacc® Value Test (YSVT®).

The response of dairy TMRs to Yea-Sacc supplementation may vary depending on the feedstuffs. Formulation models are limited in predicting the effects of non-nutritive feed additives on rumen fermentation, which limits the precision of ration formulation and the prediction of the efficacy of a given additive. A quick lab-based test that evaluates the potential of Yea-Sacc in a particular situation can help improve the nutritive value of a given TMR.

Building on Alltech IFM, an in vitro rumen fermentation model used to characterize feed digestion kinetics, YSVT is a unique approach to rumen fermentation analysis. Standard in vitro rumen simulation techniques are usually conducted over a shorter period spanning 48 to 72 hours of fermentation. As a result, these techniques do not allow for an accurate evaluation of the efficacy of yeast supplements, as the effects of yeast on rumen populations are not readily evident until supplements like Yea-Sacc have been included in the diet for at least 4 to 7 days.

As the animal adapts to the presence of Yea-Sacc in its diet, the rumen microbial population changes to comprise higher concentrations of fiber-digesting and lactate-utilizing bacteria. YSVT utilizes rumen fluid both from animals that have been adapted to Yea-Sacc and their counterparts that are fed the same basal ration without Yea-Sacc. This allows for the adequate adaptation of the rumen microbial populations to Yea-Sacc without the need for long-term incubation in the lab.

The YSVT test measures key fermentation indicators, including:

  • Digestibility
  • Lactic acid concentration
  • Useful energy (i.e., energy produced from the fermentation of carbohydrates)
  • Rumen energy efficiency (i.e., useful energy per pound of feed digested)

To date, more than 200 dairy TMRs have been analyzed using YSVT. More than 93% of the samples showed a positive response to Yea-Sacc supplementation in terms of useful energy and rumen energy efficiency, with an average response of +13%.

"Rumen Energy Efficiency"

In approximately 50% of all samples, the increase in the useful energy released was not correlated with improvements in digestibility. This indicates that Yea-Sacc increases the efficiency by which feed nutrients are converted into useful energy for the animal, most likely through a more efficient and healthier microbiome. The lactic acid response was more variable, with more than 60% of the samples showing decreased concentration, indicating a reduced risk for a lower rumen pH and acidosis.

In conclusion, the YSVT helps nutritionists and producers understand the value of yeast in improving rumen fermentation. As a result, feed additive supplementation strategies can be tailored to maximize the energy produced from rumen fermentation and improve digestive efficiency in dairy cows.  future developments of this tool will focus on better understanding the interaction of ingredients, the nutrient composition of the TMR and the response to Yea-Sacc — and on developing predictive models to quantify the expected animal performance based on the outcome of a given fermentation profile.


I would like to learn more about the Yea-Sacc Value Test.