Somewhere around 10 years ago, I began drinking wine. Prior to that, I never thought too much of the stuff, considering it the unfortunate destruction of the juice from a perfectly good grape. At the time, I didn’t know that wine should never be purchased from the refrigerator of a grocery store. Then a couple of my industry cohorts introduced me to fine wines. There are a lot of things that contribute to a wine tasting good: the variety of the grape, the type of soil in which the grapes are grown, and the sugar content of the grapes at harvesttime. Probably the most crucial aspect of making good wine is the fermentation process.
Fermentation is an amazing thing. It’s essentially the conversion of organic compounds – such as sugars or more complex carbohydrates – by bacteria or yeasts into other products such as alcohol or organic acids.
In the case of winemaking, the final product is an alcoholic beverage that’s pleasing to the palate. In the case of ruminant nutrition, feedstuffs are reduced in the rumen by microorganisms that begin the initial process of digesting fibrous plant material and produce simple fatty acids that are the building blocks for metabolizable energy in the ruminant.
In the fermentation process of grapes into wine, the end products are alcohol, CO2 and grape residue. The end products in the fermentation of both fibrous and nonfibrous feedstuffs in the rumen are primarily three fatty acids: acetic acid, propionic acid and butyric acid. Acetic and propionic acids move on to the liver, where they are converted into glucose. Butyric acid is absorbed in a different manner to supply energy to the cells. It’s important to understand that energy synthesis for dairy cows must originate in the rumen as a result of fermentation. If the fermentation process is disrupted, metabolizable energy levels are quickly reduced for the cow. Cows do not derive their energy from the intestinal absorption of carbohydrates and fat the way humans do.
Rumen fermentation begins the digestion of fibrous plant material, breaking it down so it can be further digested in the other stomach chambers. Fiber is not easily digested, and that’s why single-stomach creatures such as humans have a limited ability to digest it. Animals such as cows, goats, sheep and deer have multi-stomach digestive systems that break down cellulose-containing material in stages.
Unlike the fermentation of sugars in grape juice, which is a limited process that eventually has an end point resulting in a specific type of wine with a specific level of alcohol and taste, fermentation in the rumen of a cow is a continuous process that goes on 24 hours a day for the life of the cow. At the heart of the fermentation process in dairy cows is a multitude of microorganisms that live in the rumen – primarily bacteria, along with protozoa and fungi. Millions upon millions of these “bugs” have breakfast, lunch and dinner from the feedstuffs that we feed the cow, breaking the carbohydrates into smaller and smaller bits that eventually leave the rumen. This digesta is further broken down in the omasum and then moves into the abomasum, where it continues to be digested with acids – more along the lines of how our stomachs work.
When a cow’s diet is well-balanced, with the proper amounts of protein, carbohydrates, fiber and minerals, the bugs are the happiest as they reproduce and expand their populations, enabling themselves to ferment large amounts of feedstuffs and creating lots of acetic, propionic and butyric acids. The more fermentation acids they produce, the more energy the cow has for milk production. The more bugs there are in the rumen, the more metabolizable protein is available in the small intestine when they expire and leave the rumen.
The health of rumen bugs is very dependent upon the pH balance in the rumen. The pH in the rumen must remain in a fairly tight range between 5.5 and 6.5. Fiber digesters are happiest at the upper end of the range, while sugar and starch digesters are happier at the lower end. Over the years, nutritionists have found that even though cows are primarily herbivores that are best suited to consuming plants, they can tolerate a certain amount of nonfibrous feedstuffs – corn, barley, wheat – that provide starches and sugars that can be more rapidly fermented by the rumen bugs. However, too much sugar and starch in a cow’s diet is a recipe for disaster, causing a lowering of the pH level in the rumen, which is fatal for the fiber digesters. The cow is then suffering from rumen acidosis.
If the fiber-digesting bugs are put out of commission, fermentation comes to a screeching halt and microbial populations decline, reducing both energy and protein metabolism. Milk production is the first thing to suffer. If a cow’s rumen stops functioning, obviously energy production ceases. The resulting empty abomasum can displace and twist, leaving the cow in a potentially lethal situation.
While there are opportunities to maximize rumen fermentation with grains and nonfibrous byproducts, a cow’s rumen is primarily designed to utilize fiber as its primary source of nutrition. Healthy dairy cow diets should focus first on high-quality forages that provide highly fermentable fibers that will enable rumen bugs to flourish.
Much time and effort is put into the creation of a fine wine, making sure the sugars, the yeasts and the temperature are just right. The same amount of effort and care should go into balancing the diet of a dairy cow, maximizing the fermentation in her rumen and making the rumen bugs happy.