Current Progressive Dairyman digital edition

4 questions to ask about yeasts

Troy Wistuba for Progressive Dairyman Published on 08 November 2018
calf eating

You add it to bread to make the dough rise, and you use it to ferment beer and wine. But why feed yeasts to your herd?

Yeast additives help support forage digestion and promote gut health. That’s the simplest explanation, but it gets a bit more complicated as you dig in further. What criteria should yeasts meet? When do you feed yeast? And what’s the difference between yeast and yeast cell wall?



To steer you in the right direction, here are four common yeast questions answered:

1. What is yeast?

There are three main types of yeast products available for dairy calves – live yeast, yeast culture and yeast cell wall (YCW). Yeasts are microscopic fungi. Their primary use is to promote rumen fermentation and improve fiber digestion.

Yeast culture contains both the yeasts and the culture they are grown in. Yeast culture is used to improve dry matter intake, enhance rumen fermentation and improve fiber digestibility.

YCW is created by removing the contents of the yeast cell and leaving behind only the cell wall. YCWs help stimulate an immune response and protect calves from pathogens.

Along with prebiotics and probiotics (covered in the first two articles of this three-part series), yeast products are another tool to reduce dependence on antibiotics without sacrificing performance.


2. Why should I feed yeasts?

Yeasts, yeast cultures and YCWs help support calf gut health, but they contribute in unique ways. Yeasts function primarily in the rumen, while YCWs are active in the lower gut. Yeast cultures appear to have both rumen and lower gut functionality.

When live yeasts reach the rumen, they consume any oxygen present, allowing anaerobic bacteria, or rumen microbes, to thrive. Microbes ferment the grains and forages in a calf’s diet, allowing for better nutrient absorption.

Anaerobic microbes in the rumen such as protozoa, bacteria and fungi digest feed in the rumen, which provides nutrients to the calf. Without proper management of these microbes in the gut environment, calves can be at risk for severe illness, such as acidosis. Thanks to its ability to promote a more stable rumen pH level, live yeasts can positively impact the rumen microbes to promote good rumen function and reduce calves’ risk for acidosis.

While prebiotics and probiotics focus on supporting good bacteria, YCWs’ job is to block the bad bacteria. YCWs stimulate immune function by preventing disease-causing bacteria from attaching to the intestine and multiplying. They also encourage villi growth for increased nutrient absorption capacity, which is especially beneficial to calves undergoing rapid growth.

3. Which yeasts should I choose?

There are two main differences between yeast additives on the market. One is whether they contain live or inactive yeast cells. The other is if they offer a colony-forming unit (CFU) guarantee. Yeast product types include:

  • A live, dried product with a guaranteed CFU
  • An inactive and soluble culture with no CFU guarantee
  • A blend with live and inactive yeast, sometimes offering a CFU guarantee

Live yeast contains live yeast cells, while inactive yeast is yeast that’s been killed through a pasteurization or sterilization process but maintains its nutritional value. A CFU guarantee is used to confirm the number of live yeast included in the product.


The science community isn’t certain which kind of yeast works best, but there’s one thing research confirms: Live, inactive and combination yeast products can all provide digestive benefits for your herd.

Selecting a product that contains both yeast and YCWs can be beneficial if you’re looking to capitalize on the benefits of both.

calf starter

4. When is the best time to feed yeasts?

Yeasts and YCWs are beneficial to your herd year-round. There’s no wrong time to feed them, but there are times when calves and heifers need them most.

Yeasts offer the most benefit to calves and heifers:

  • At risk for heat stress
  • Starting a new diet
  • Experiencing forage or feed changes

Yeasts are most commonly fed to post-weaned heifers to support rumen health and nutrient absorption from an all-forage diet. They can be found in starter and grower feeds, or can be added to the diet as a supplement. Yeasts are also commonly supplemented in the adult cow ration, especially for transition cows and early lactation cows.

Because of their role in supporting the immune system, YCWs offer the most benefit to:

  • Animals facing pathogen challenges
  • Milk-fed calves

YCWs may be included directly in your milk replacer or can be added as a supplement. Some feeds and supplements already contain both yeasts and YCWs. Double-check your feed labels to see if yeasts and YCWs are included.

Contact your local calf and heifer specialist to discuss adding yeasts to your herd’s nutrition program.  end mark

This article completes a three-part article series about probiotics, prebiotics and yeasts. Read about probiotics in part one, or read about prebiotics in part two.

Troy Wistuba
  • Troy Wistuba

  • Director of Dairy Technical Innovation
  • Land O’Lakes
  • Email Troy Wistuba

PHOTO 1: Pre-weaned calves need extra nutritional support to help their immune systems prevent and fight off disease challenges.

PHOTO 2: Yeasts can be found in starter and grower feeds or added to the diet as a supplement. Photos courtesy of Land O'Lakes.

Before commenting on our articles, please note our Terms for Commenting.