Without a doubt the single-most unique aspect of dairy cow nutrition is that it must focus on a complex and multi-chambered digestive system.

The ruminant species which includes not only cows, but goats, sheep, deer, moose, llamas and alpacas, have been created for the purpose of utilizing, for much of their diet, plant material that simple-stomached critters like ourselves could never hope to eat. This all happens because of a process called fermentation that occurs in the largest of the four digestive chambers called the rumen.

When we talk about fermentation many of us may think of brewing beer or baking bread. Those two industries account for the lion’s share of fermentation intended for human consumption. Dairy farmers will also be acquainted with the fermentation process in the ensiling of corn, cereal grains and other forages.

Well, forget all the millions of gallons of beer, loaves of bread and tons of silage that are produced each year. Pound for pound, ruminants all around the world have beer, bread and silage beaten by many multiples when it comes to the fermentation of organic matter.

Fermentation as it applies to the rumen refers to the bio-conversion of complex carbohydrates into smaller molecular units that are then absorbed, either directly from the rumen, or through the intestinal wall to be utilized as energy. Fermentation in the rumen is that process that allows fibrous plant material – plants that simple-stomached creatures can’t digest – to be consumed by dairy cows and other ruminants.

The key to making any fermentation process happen is the presence of billions of bacteria, protozoa and fungi. The rumen is nature’s wonderful way of allowing animals such as dairy cows, goats and sheep to utilize forages that are high in cellulose such as pasture grasses, corn stalks and even weeds that can be converted into food and fiber.

It’s the way undomesticated animals like deer, elk and moose can survive in the wild. It’s the way exotic beasts of burden like camels, alpacas and llamas can survive in harsh environments.

For the modern dairy cow, the rumen has to be healthy in order for the cow to be productive. The rumen must function continuously and consistently, around the clock in order for dairy cows to produce the thousands of pounds of milk they do.

Any disruption in feed supply or a drastic change in diet will disrupt the work of the rumen microbes. They are the only means by which feedstuffs are converted to energy and metabolized by the cow. When they are reduced in number for any reason, cow health and milk production suffers.

During the past 40 or 50 years, dairy scientists and researchers have spent a considerable amount of time in an effort to understand the complexities of the rumen function. What we’ve always known is that, in order for a rumen to function correctly, fibrous feedstuffs such as grass and hay are the foundation of a dairy cow’s diet.

All dietary fiber delivers certain fractions of various carbohydrates to the digestive system, most of which is eventually converted into metabolic energy for the cow. The challenge for ruminant scientists and dairy farmers is to feed those carbohydrates that are soluble and therefore quickly fermented while at the same time provide adequate fiber retention that keep rumen microbes in the rumen long enough to accomplish the fermentation.

For dairy cows the more soluble carbohydrates such as starches and sugars will be utilized by rumen microbes more rapidly than pectins, fructans and other polysaccharides found in sugar beet pulp or citrus pulp. Cellulytic carbohydrates found in overly mature forages are the least soluble of carbohydrates.

The key to keeping a rumen happy, healthy and balanced is to avoid the over-use of starches and sugars and focus on soluble fibers in high-quality forages or byproducts. In an effort to balance carbohydrate fractions and avoid an acidotic rumen situation that seriously hampers fermentation, nutritionists suggest keeping non-fiber carbohydrates (NFC) balanced between 32 percent and 38 percent of dry matter intakes when feeding higher levels of grains like corn and barley or byproducts like wheat midds, hominy and distillers grains.

When rations contain high-quality hay, haylage, BMR corn or sugar beet or citrus pulp, and the effective fiber is adequate, NFC can range from 38 percent to 42 percent of total dry matter intake. (Note: The Penn State Particle Separator is a useful tool in determining effective fiber levels in a ration.)

Keeping the pH level in a rumen between 6.0 and 6.5 is the generally accepted range to support good fermentation in the rumen. High-starch diets will produce acids that will drive pH below 6.0, which creates a hostile and unproductive environment for fiber-digesting bacteria. Continued low rumen pH levels will eventually result in clinical acidosis for the cow and a rapid decline in milk components, milk production and health.

The proper balancing of feed rations for our dairy cows is first and foremost about creating and supporting a healthy microbial population in the rumen. The greater the number of microbes in a rumen, the more fermentation that can be accomplished. The more fermentation there is in a rumen, the more energy that’s available for the cow’s use. The more microbes working in the rumen also means more microbial protein that will be available for metabolic absorption.

When the bugs in the rumen are happy, the cow will be happy. When cows are happy, dairy farmers are happy, too. PD

John Hibma
Nutritionist
hibmajl@cox.net