Editor’s note: This is the second in a two-part series on feed additives and supplements. Click here to read the first of the series (More additives, supplements than you can shake a stick at).

Even before the dairy industry began to seriously focus on feed efficiency (FE), an entire industry had been built on an ever-growing number of additive products designed to be fed to the animal.

Initially, the goal of the use of such products was to improve milk and component production, improve animal health and reproduction and, ultimately, increase on-farm profitability.

Now we look at these products and what they can do to improve FE, but the end game is to improve farm profitability (more specifically, income over feed costs).

These tools, both individually and in combination, can have a marked effect on herd and farm performance – but remember, there are no magic bullets and no replacements for sound management.


The challenges nutritionists and dairymen face when evaluating additive products are that in many cases:

  1. The results shown in available research is not replicated on the farm or cannot be observed.

  2. In some cases, products are marketed with very little research or from a “me-too” perspective (i.e., “our product is just like XYZ, just cheaper”).

  3. Product effect is highly variable because of variation in diets, rumen conditions, management, feeding programs, environment, etc.

  4. If products are “stacked,” meaning more than one is used in a given ration, there is no accurate prediction of how these products may interact or the results the combination will produce.

    As mentioned, in many cases there is not a lot of research for some of these types of product. There is far less research on combinations. Since most of these types of additives modify rumen function or the rumen microbial population in some manner, there is always a possibility of an antagonistic effect.

  5. In periods of depressed milk or component prices, the added cost that comes with the use of these types of products can make inclusion justification difficult. The pressure on any given product to “pull its weight” economically is significant.

Commonly used additives

In the world viewed as modern dairy nutrition and feeding, the list of additive types is extensive. As mentioned in Part 1, some of the most common are:

  • Yeasts
  • Yeast derivatives (cell wall components or isolates)
  • Direct-fed microbials (bacteria and fungi)
  • Essential oil/plant extracts (many types and combinations)
  • Enzyme sources (may actually fall under the direct-fed microbial category)
  •  Antibiotics (i.e., Rumensin)
  • Dewormers
  • Toxin binders
  • Rumen buffers

Obviously, there is not room to fully analyze each of these categories, but a few will be discussed here. Just recognize that each of these can affect the rumen microbial population and play a specific role and produce a specific response in the lactating animal. Let’s look at a couple of examples.

Yeast products

Yeast has been included in dairy rations for years. Since then, a huge number of yeast products and product types have been developed for use in dairy diets. With all the variation comes a lot of discussion and argument over which products are most effective in improving animal performance and FE.

There are essentially two yeast product types. The first is inactive (or killed) yeasts, which include yeast cultures, yeast concentrates and other derivatives (these may now include bacterial cultures and fungal cultures that may subsequently claim enzymatic activity). The second is active (live) yeasts.

The inactive or killed yeasts are exactly that: yeast cells not capable of division, respiration or other metabolic activities. They are largely a concentrated nutrient source for the rumen microbial population. In a number of cases, these yeast products include significant amounts of the media upon which the yeast itself is grown.

This media is generally a grain base of some type. So the product is a blend of yeast cells, growth media and any metabolic products the yeast cells may have produced in the growth process. With microscopic examination, some of these products contain relatively little actual yeast.

There are inactive yeasts that are more “pure.” These are essentially 100 percent dried yeast cells higher in the cell contents that are nutrient sources for the rumen microbes and include providing specific nutrients such as proteins, peptides, amino acids, organic acids, nucleotides, minerals and vitamins.

These types are also a source of cell walls and cell wall components which are largely insoluble in the rumen but have been shown to have an immunostimulatory effect in the intestinal tract.

Live or active yeasts are commonly delivered in a freeze-dried form and, when rehydrated, will become active in the rumen. The primary hypothesis of how live yeasts “work” is that their reproduction and metabolic activity utilizes oxygen in the rumen.

By scavenging the oxygen from the rumen, this creates a more favorable environment for rumen microbiota (particularly fiber-digesting bacteria), thus allowing them to function more efficiently.

Other modes of action have been suggested, including stimulus of lactic acid-utilizing bacteria and improvement in microbial protein production.

A potential challenge with the use of live yeast is that they must be packaged and handled in a specific manner in order to preserve viability. Live yeasts must be stored at the dairy and added directly into the mixer in order to maintain their activity to the point of feeding.

There has been discussion as to whether a live yeast product is truly alive by the time it reaches the cow. Finally, live yeasts are typically fed at a much lower level than inactive yeasts. This may or may not be an advantage.

All this said, and while research of these products has been conflicting and varied, in general, yeasts are considered beneficial in the dairy diet.

Yeast feeding is expected to help stabilize rumen function, help support pH during increased starch feeding, improve fiber digestion, help ease stress effects and, ultimately, improve milk production, support components and improve FE.

Like any additive, the producer should expect a positive return on investment with yeast feeding. Exactly what that return on investment should be is hard to define, often because we do not have a clear starting or comparison point.

Nonetheless, if adding or changing yeast, it is important to have a good idea of what production, FE and return on investment has been for several months leading up to the point of ration change.

Essential oils

Essential oils, also known as plant extracts, are a relatively new additive to the dairy industry. They are shown to have some efficacy in modifying rumen activity for more efficient performance, thus improving FE.

The complicating factor with evaluating and selecting an essential oil product is that there are many different products, and these products are combinations of two or more (generally more) individual essential oils that have been shown to have one effect on the rumen microbial population or another.

There are dozens, maybe hundreds, of compounds extracted from various plants that can be described as essential oils and that have some type of an effect on the bacterial population in the rumen when fed. These include capsaicin from hot peppers, limonene from dill, cinnamonaldehyde from cinnamon, allicin from garlic and many others.

Essential oils are being considered as a way to improve or alter rumen fermentation with naturally occurring compounds rather than commercial additives or antibiotics.

Primary objectives in altering rumen fermentation include reducing gas production (particularly methane) and increasing propionate and butyrate production, resulting in more efficient growth of the rumen bacteria. Essential oils may affect the cell membranes of gram-negative bacteria (similar to Rumensin), or others can act within the cell of gram-positive bacteria.

While much of the work with essential oils has been done in vitro, there is limited data available from trials with lactating cows being fed essential oils. Some of the farm studies have shown increases in dry matter intake as well as butterfat when an essential oil blend was fed.

Other studies have reported results including increased milk production and increased components including an increase in fat-corrected milk yield. While there is still a great deal of research needed, particularly in fine-tuning the blends or better determining which specific essential oil does what, it is generally believed that feeding an essential oil can produce a return on investment of between four and five to one.


These are only brief and limited examples of the types of effects that can be noted when feeding various additives. And as helpful as it would be, research comparing products and product types is very limited.

The best strategy is for the dairy producer and nutritionist to evaluate as many of the products and potential combinations as possible on a case-by-case basis. And remember: These products may function differently depending on forage type and quality and thus may require re-evaluation once new feed sources are introduced.  PD

Steve Blezinger