Author Archives: Troy Downing

Ruminants are more important to the world than you might have thought!

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It is estimated that the world’s population is around 7.4 billion people. The US population recently climbed past 300 million people, as we continue to add a new person every 7 seconds. The United Nations projects that the world population will increase to 7.9 billion people by 2020. The huge majority of this growth (95%) will be in developing countries, where 77 percent of the world’s population already lives. These developing countries are also increasing their per capita consumption of meat, milk, and eggs.  Thus, the demand for animal products is expected to increase more rapidly than the total population.

I have listened to people debate the issue of feeding this ever increasing population and have wondered what needs to be done to continue to provide nourishment for all these people. Many argue we have no food shortage currently; we just have populations that are too poor to grow or purchase food. Regardless, I think feeding the world’s residents is a major challenge in years to come. I am convinced ruminant animals have a significant role to play in the solution.

I know my children have questioned for years why I get so excited about cattle and grass. I have tried to explain the unique role ruminants play in our lives, but I still am not sure they are excited as I am. Globally, around 55% of the world’s land is classified as pasture, grasslands, meadows, or forest-pastures that have the potential to produce 5.8 trillion Mcal of metabolizable energy. Around 50% of the 1.9 billion acres in the US is classified as range or pastureland. This is an extremely large resource that already is or can be used for food production.

Grazing ruminant animals is an efficient way to produce food for humans. Grazing animals on land that is unsuitable for crop production more than doubles the land area in this country that can be used to produce food. Ruminant animals can use plant cell walls as a major source of dietary fiber and energy. The polysaccharides in plant cell walls cannot be degraded by mammalian enzymes, which is why humans cannot effectively use grass as food.  However, ruminants are uniquely adapted mammals that depend on microbial fermentation in one of their stomachs, the rumen. With this adaptation, ruminants are especially capable at using plant fiber for energy. Fiber, measured as neutral detergent fiber (NDF), usually accounts for 30-80% of the organic matter in forage crops. The remaining organic matter is almost completely digestible by a ruminant’s own enzymes. It is this unique digestive system that allows ruminant animals to consume poor quality forages and transform them into high quality meat and milk. And because so much of the world is covered with range and pasture lands, it only makes sense that sustainable communities and sustainable agriculture include grazing animals.

Over the years, critics of animal production have argued we should be feeding human-edible foodstuffs (grains, protein sources, etc.) to only humans and not include these in ruminant diets. Too often the opponents of animal agriculture evaluate the desirability of animal production on gross calorie or protein intake/output values, with an assumption that all animal feed could or would be eaten by people. However, in many cases the feeds used in animal production are not consumed nor consumable by humans, and in order to properly evaluate animal production, only human-edible consumable energy and protein intake should be used for efficiency comparisons.

Many studies and evaluations have been conducted looking at the efficiency of livestock in converting plant based protein and energy into animal products. Non-ruminant animals like swine and poultry, cannot utilize low quality forages like ruminants can, but they are really efficient in their ability to gain weight eating grains. Ruminants, on the other hand, are less efficient in converting grains to animal protein. However, they can maintain and produce on a diet of 100% forage or by-product feeds if necessary. In fact, dairy cattle and goats are quite exceptional in being extremely efficient in converting plant-based protein/energy sources into high-quality animal fats and proteins. I believe the evidence that ruminant livestock belong in sustainable livestock production systems is convincing.

Ruminants have served and will continue to serve a valuable role in sustainable agricultural systems. They are particularly useful in converting vast renewable resources from rangeland, pasture, and crop residues or other by-products into food readily eaten by humans. With ruminants, land that is too poor or too erodible to cultivate becomes productive. Nutrients in all kinds of by-products are utilized and do not become a waste-disposal problem. In Oregon, waste products from the grass seed, vegetable, nut, tree fruit, and berry industries as well as brewing wastes are being fed to livestock.  It is clear to me ruminants are essential components in food production systems now and in the future.

How do cows digest all that feed they eat?

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Lactating cows can eat upwards of 55 pounds of feed a day on a dry matter basis. How do they do that?  Ruminants produce large quantities of saliva every day. Estimates for adult cows are in the range of 25 to 38 gallons of saliva per day. Aside from its lubricating qualities, saliva serves at least two additional very important functions in the ruminant. It plays a major role in buffering the pH in the foregut and provides fluid for the fermentation activities in the rumen. Boluses of preliminarily chewed forage are regurgitated from the reticulorumen and re-chewed: the process we refer to as rumination or cud chewing. The grinding action of the teeth mechanically breaks down the plant fibers into smaller particles, providing additional surface area for digestive enzymes to “attack”. Animals on pasture or range typically graze for around 8 hours a day, providing a steady stream of feedstuffs to the reticulorumen. Contractions mix the feed around and between the rumen and reticulum. See Figure 1 for a diagram of a typical ruminant digestive tract.

outline of a cow with detailed labeling of the digestive tract: mouth, esophagus, reticulum, rumen, omasum, abomasum, small intestine, large intestine
Figure 1 – Illustration of the digestive system in a cow.

The rumen is essentially a fermentation vat. We have often heard cows have four parts to their stomach, the rumen in the largest section in this stomach series and tend to get most the attention because of its unique capabilities. It provides an anaerobic environment, constant temperature and pH, and thorough mixing that allow the microbes to digest forages. Bacteria, protozoa, and fungi are the three major types of microbes. Figure 2 illustrates the types and approximate numbers of microbe types in a rumen (and the number of humans on Earth, just for comparison). Mammals don’t produce enzymes that can digest plant fibers like cellulose. Cattle and other herbivores rely on the digestive enzymes produced by their gut microbes in order to get the majority of nutrients out of forages.

bar graph showing numbers of bacteria, protisis, fungi, mycoplasma, and viruses in a rumen. Also shown is the number of humans on earth for comparison. Data courtesy of Mel Yokoyana, Michigan State University.
Figure 2 – Illustration of microbe populations typically found in the rumen. The scale on the left is logarithmic.

The rate of flow of solid material through the rumen is quite slow and dependent on feedstuff size and density. However, water flows through the rumen rapidly and appears to be critical in flushing particulate matter downstream. As fermentation proceeds, feedstuffs are reduced to smaller and smaller sizes and microbes constantly proliferate. Ruminal contractions constantly flush lighter solids back around the reticulorumen while denser particles (feedstuffs that have been there longer) proceed to the omasum.

The function of the omasum is rather poorly understood. It may function to absorb residual volatile fatty acids and bicarbonate. The tendency is for fluid to pass rapidly through the omasal canal, but for particulate matter to be retained between the omasal leaves. Periodic contractions of the omasum knock flakes of material out of the leaves for passage into the abomasum.

The abomasum is a true, glandular stomach which secretes acid (significantly lowering the pH) and otherwise functions very similarly to the stomach of a monogastric. One fascinating specialization of this organ relates to its ability to process large masses of bacteria. In contrast to the stomachs of non-ruminants, the abomasum secretes lysozyme, an enzyme that efficiently breaks down bacterial cell walls. Much of the protein need of the ruminant is actually satisfied by digesting bacteria that have traveled from the rumen.