Feed programs that nurture rumen microbial populations help increase the dairy’s income over feed cost (IOFC). Rumen microbial populations play a pivotal role in converting feedstuffs to high-quality microbial protein and volatile fatty acids (VFA), which serve as energy sources.

Oelberg tom
Ruminant Field Tech Specialist / Diamond V
Thomas Oelberg has a Ph.D. in dairy nutrition from Ohio State University and is employed by Diamo...

The greater the rumen microbial populations, the more efficient the conversion is.

Microbial protein, VFAs and nutrients that escape (bypass) the rumen support all the cow’s body functions. Efficient dairy rations, then, are those that maximize rumen microbial populations and the microbial end products they generate while minimizing the need for dietary bypass proteins, fats and starches.

Simply put, the greater the rumen microbial populations, the more efficient the rumen is in converting feedstuffs to proteins and VFAs.

Promoting rumen performance

Managing rumen performance includes feeding an all-natural, fermentation-based feed additive (yeast culture) composed of numerous beneficial metabolites.


It is the metabolites in yeast culture, produced during anaerobic Saccharomyces cerevisiae fermentation, that support dairy cow health and performance. The practice began during the early to mid-1900s. In the past 70 years, extensive research – both in-breadth and in-depth – has increased our understanding of how and why the fermented yeast culture product impacts production and performance throughout the lactation cycle.

Rumen microbial populations respond to the beneficial metabolites in fermented yeast culture and its nutritional metabolites. Populations of both fiber and starch-digesting microbes increase significantly. As these populations multiply, they more thoroughly digest feedstuffs.

This means feedstuffs are more thoroughly broken down and more of the nutrients they contain become available for use.

Rumen fermentation produces the VFAs acetate, propionate and butyrate. Each can be used for energy and fat synthesis. Propionate is the primary VFA used for glucose production.

That is significant. In the mammary gland, glucose is converted to milk lactose. The supply of propionate, then, drives milk production. Feeding fermented yeast culture and its nutritional metabolites promotes higher propionate levels and higher milk production.

Year-round benefits

The production benefits from greater rumen microbial efficiency continue year-round. Transition cows maintain higher dry matter intake (DMI) for better body condition and fewer metabolic problems. The fresh cow’s rumen is in excellent condition.

Its efficiency allows her to reach a higher peak milk production. This feed efficiency continues with later-lactation cows which achieve a higher total milk of lactation. With dry cows, the higher level of DMI prepares them for a better transition to lactation.

Top managers typically keep the fermented yeast culture in the ration year-round because the full benefits are realized after approximately three weeks of feeding. They don’t want to risk having diminished rumen efficiency at transition.

During periods of heat stress, fermented yeast culture continues to support high productivity and performance. Generating more propionate, more glucose, during heat stress supports better cow health and performance.

The heat-stressed cow naturally prefers to use glucose for energy rather than her own body fat because glucose generates less body heat. Before making ration adjustments for summer heat, though, be sure to fully use mechanical cooling such as shade, fans, soakers, etc.

During heat stress, producers also are encouraged to feed high-quality, highly digestible forages to minimize heat production in the rumen. Rumen temperatures typically run a little higher than the cow’s body temperature, a good thing during cold weather but a contributor to discomfort during heat stress.

Heat stress occurs when the thermal heat index (THI) reaches 68. The THI takes into consideration both temperature and humidity. Heat stress, for instance, can occur at 72 degrees Fahrenheit and 45 percent relative humidity, which may seem comfortable for people.

Fermented yeast culture also has benefits for feed managers and feeders. They offer a highly consistent, hassle-free product for daily use. The product is not affected by heat, cold or rough handling. Its shelf life is long even when used in mineral packs or stored on-farm.

As today’s dairy nutritionists and top dairy managers formulate rations to maximize milk production and performance, they include a fermentation-based feed additive (yeast culture) every day in every ration to stimulate the growth of rumen microbial populations.

They know that the larger the rumen microbial populations are, the more efficient the rumen will be for greater feed efficiency and IOFC. PD

Oelberg has a Ph.D. in dairy nutrition from Ohio State University and is employed by Diamond V as a dairy technical service specialist based in Minnesota.

Thomas Oelberg