Livestock Farmer

cow line

Grazing School.... Science lecture on digestion gets to basics

LINNEUS, Mo. -- Cow spit is a wondrous juice that makes grass digestion possible. That was just one part of the lesson on "Livestock Nutrition on Pasture" for those attending a Grazing School at the University of Missouri Forage Systems Research Center.
The terminology was more scientific at first, but K. C. Olson,
nutritionist with the extension Commercial Agriculture beef team, soon broke it down into terms that any farm kid could understand. For example, saliva is spit and eructation is belching. It's all part of what Olson calls "a wonderful process" that breaks down cellulose, the fiber in forage, into usable energy.

He explained that a ruminant animal -- a cow, sheep or goat -- has four stomachs to ferment and digest plant materials that other animals can't eat. What makes ruminant animals unique is their ability to digest the cellulose and hemicellulous that make up 85 percent of all carbohydrates on earth. Animals with gastric stomachs, including humans, pigs and chickens, can digest only 15 percent of the energy produced by plants.
The ability to eat forage helps make beef animals the number-one
agricultural enterprise in Missouri. The state produces a lot of grass that could not be used otherwise, the grazing school faculty explains Jim Gerrish, MU research agronomist and head of the school, said that participants in the school are at the stage where they want to learn more about the science of grazing. The aim is to improve the efficiency of the process. Explaining cow spit, Olson said a small set of glands located around the cow's jaws generates up to 30 gallons of juice, or saliva and mucous, that helps moisten and lubricate the forage so it can be swallowed and digested. "The salivary glands allows a beef animal to take in a huge amount of dry matter every day," Olson said.

The rumen holds a barrel full of feed and fluids, from 55 to 70 gallons in a mature cow. The fluids, including that cow spit, help break down the fiber in a process that takes up to 96 hours. To increase grazing efficiency, the cow takes in a large amount of forage quickly. She swallows her food whole. Later, usually while lying down, she belches up a cud of grass to re-chew leisurely. The cud chewing grinds fiber into particles small enough to digest. A cow roughly divides her time into 8 hours of eating, eight hours of cud chewing, and eight hours of resting.  She doesn't do those jobs all at once but breaks them up into short spans, Olson said. That keeps an even flow of feed going into her fermentation tank or the rumen that is one of four extra stomachs.
If Olson gets excited about cow spit and cud chewing, he really is in awe of the process inside of the rumen where "millions and millions" of microbes go to work on the fine forage particles. This gets into biochemistry. The microbes, including bacteria, protozoa, fungus, and viruses, break down plant materials into usable components such as volatile fatty acids, amino acids, peptides, ammonia and other elements.

And, that soon gets into methane gas -- and belching, burping, and other gas emissions.
Maybe you just have to be there.
Source: K. C. Olson (573) 882-7289

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