Rumen Physiology for the Rancher

Beef specialist discusses factors that enhance, hinder rumen function, the digestive process and its effect on animal performance.

by Troy Smith for Angus Productions Inc.

 

CASPER, Wyo. (Dec. 3, 2009) — Most people attending the 2009 Range Beef Cow Symposium in Casper, Wyo., probably possessed a basic understanding of the cow’s digestive system. Most ranchers know a cow is a ruminant. They know a ruminant chews a cud and is equipped with a four-compartment stomach. And most ranchers know this peculiar digestive system is the reason ruminants can convert forages into high-quality protein — the beef that provides nutritious and enjoyable eating experiences for humans.

 

When the level of grain surpasses 5% of the diet, the shift in rumen microbe population begins and forage digestibility starts to decrease, Ivan Rush explained.In comments delivered during the symposium, University of Nebraska Extension Beef Specialist Emeritus Ivan Rush acknowledged his audience’s familiarity with cattle. But it couldn’t hurt, he added, to review some general ruminant physiology.

 

“When I first enrolled in an animal nutrition course, I felt this area was unnecessary. All I wanted to learn was does the cow need one or two pounds of a supplement. I didn’t want to worry about the theory of digestion in the rumen,” Rush admitted. “Over the years, it became obvious that the better we understand how the rumen functions in breaking down or digesting feeds, the better nutrition decisions we can make when feeding cattle.”

 

Rush offered the audience a brief review of rumen anatomy and physiology. He discussed the roles of different microbes present in the rumen for breaking down dietary fiber or starch to be utilized for energy. Rush went on to discuss factors that can enhance or hinder rumen function, the digestive process and its effect on animal performance.

 

“Ultimately,” Rush added, “these factors affect the economics of cattle production.”

 

The level of starch (from grain) in ruminant diets affects the rumen microbial population. According to Rush, small amounts of starch have little effect on digestion, but higher levels of starch will increase rumen acidity — a condition less favorable to microbes, which specialize in fiber digestion.

 

Interestingly, adding a relatively small amount of grain to the diet will actually stimulate fiber digestion. However, when the level of grain surpasses 5% of the diet, the shift in rumen microbe population begins and forage digestibility starts to decrease.

 

“This does not mean we should not feed a mixture of grains and forages,” Rush stated. “Economics of the ration should determine the level of concentrates, such as grains, to be included in the diet.”

 

Rush explained that rumen organisms require a source of nitrogen, which is provided through dietary protein. Providing supplementary protein to cattle can enhance rumen microbe activity and thus increase digestion of low-quality forages.

 

Not all protein supplements are the same. Rush noted how byproduct feeds, such as those derived from the processing of corn ethanol or sugar beets, can be good sources of supplemental protein. Additionally, they are good sources of energy in the form of highly digestible cellulose and can have a complementary effect on forage diets. Starch, which has a negative effect on forage-friendly microbes, is removed from byproduct feeds.

 

Rush said feed additives containing ionophores (Rumensin ® and Bovatec ®) can also enhance digestion among ruminants. These feed additives increase the level of propionic acid relative to other volatile fatty acids in the rumen. Propionic acid, according to Rush, is more efficiently converted to blood glucose for efficient energy utilization.

 

Rush also discussed direct-fed microbial products, sometimes referred to as “probiotics,” saying they have little if any effect on fermentation in normal, healthy functioning rumens. He added, however, that data show direct-fed microbials (beneficial bacteria) are of limited benefit for improving rumen function in stressed cattle. Similarly, Rush said, enzymes probably have limited value in diets of cattle with functioning rumens, but may be beneficial to baby calves or stressed animals.

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