In a range situation, Bowman says microbes that digest cellulose have the competitive advantage, and adding energy supplements encourages the reproduction of microbes that digest starches.

“Microbes that prefer starch have a faster growth rate. They can reproduce and increase their numbers very quickly, and they can also break down starch very quickly, producing volatile fatty acids, or energy, at a much faster rate,” she says.

If starch is added to the diet rapidly, specific microbes will convert it to volatile fatty acids so quickly that the pH in the rumen will drop, she explains. Since the cellulose-digesting microbes don’t like a low pH, they won’t prosper as well in that situation, and the depression of cellulolytic digesting microbes can result in reduced fiber digestion. That will cause feedstuffs to move slower through the digestive tract, and result in reduced intake by the animal.

“You want to create a situation where you balance the diet, and the microbe populations, to garner the best utilization of everything that cow is consuming,” Bowman says.

McAllister suggests a supplement high in fiber to aid in digesting low-quality winter forages; it will also complement any nutrients not present at adequate levels in the forage.

Bowman lists protein, or nitrogen, as another key ingredient for rumen microbe health and growth in any situation. Microbes themselves are a key source of protein to the animal, and ensuring adequate protein is available to rumen microbes will benefit digestion and performance in any environment.

“We need to remember that what we’re feeding first in a ruminant are the microbes, because they have first access to producing usable energy from a feedstuff. If we make sure we’re meeting their needs so they can do their job, the entire animal will benefit,” Bowman concludes. 

Heather Hamilton is a rancher and freelance writer based in Lance Creek, WY.