by: Stephen B. Blezinger

Part 3

In Part 2 of this series on feed additives we discussed the applications of different direct-fed microbials. These products included different cultures of bacteria, yeast and fungi. These products function in a variety of capacities in the digestive tract in the animal largely to improve the overall digestive process, either in the ruminal system or in the intestinal tract.

But over the years research has found that not only these organisms themselves are beneficial to the animal. Science and the feeding industry have identified components of the cells, particularly yeast cells, that have beneficial properties when fed to animals. The most common of these are known as mannan oligosaccharides (MOS) and Beta Glucans (β -glucans or BGs). Each of these are fairly complex carbohydrate molecules which are beneficial to the animal both in the digestive tract and in the animal's system.

Both products have been researched and used extensively in the poultry and swine industry. It is often believed that these compounds, when fed to a mature cow, will be broken down by the rumen bacteria and with subsequently be of little or no value. However, more recent work has shown benefit in different applications. This has proven true especially in very young calves but also in mature animals as well.

The next sections will discuss both of these products in detail.

Mannan Oligosaccharides (MOS)

Carbohydrates (starches, fibers) are very similar in molecular structure. Changes in how molecules are attached on one another can designate whether the resulting structure is a starch (more soluble) or a fiber (less soluble). Most of the time these compounds are found either in the plant cell or in the cell wall. Aside from their nutritional value, in many cases these structures can have other functions as well in the digestive tract or in the body

Mannan Oligosaccharides are extracted from the cell walls of yeast cells (which can be considered plants). The most common of these yeasts is Saccharomyces cerevisiae. This is a variety of yeast that is commonly fed to most species of food animals. In the yeast cell wall, MOS are present in complex molecules that are linked to the protein component of the cell. To get technical for a moment, there are two main locations of MOS in the surface area of the yeast cell wall. They can be attached to the cell wall proteins as part of –O (oxygen) and –N (nitrogen) glycosyl groups and also constitute elements of large α-D-mannanose polysaccharides (α-D-Mannans), which are built of α-(1,2)- and α-(1,3)- D-mannose branches (from 1 to 5 rings long), which are attached to long α-(1,6)-D-mannose chains.

OK, all that means approximately nothing to the typical producer. What that means is the structure that is created on the surface of the cell is very attractive to water and creates variable ‘brush like' structures that can fit to various attachment locations in the animal's digestive tract. It also allows for binding to receptors on the surface of bacterial membranes affecting the bioactivity of these molecules. The MOS-protein combinations are involved in interactions with the animal's immune system and as a result enhance immune system activity. They also play a role in animal antioxidant and antimutagenic (cell mutation) defense.

The point to all this is that the MOS structures, which can be extracted from the yeast cell wall, can serve to attach to surface areas on animal's intestinal wall. In some cases this MOS attachment can aid with nutrient absorption. In other situations it can prevent pathogenic organisms from binding to the intestinal membranes where they can invade the body (competitive inhibition). Finally, MOS can function to enhance the performance of the immune system.

The initial interest in using MOS to protect gastrointestinal health originated from work done in the late 1980s. At this time researchers looked at the ability of mannose, the pure version of the complex sugar in MOS, to inhibit salmonella infections. Different studies showed that salmonella can bind to mannose. The binding to mannose reduces the risk of pathogen colonization in the intestinal tract.

The digestive tract is the largest organ in the body and is home to billions of microorganisms. Even more so in the case of the ruminant which includes the rumen as part of its digestion system which is a huge fermentation vat, full of microbes. Nutrition must not only provide the necessary nutrients, it must also support a balanced microflora. In recent years consumers and the media have placed an ever greater emphasis on wellness, energy levels and overall well-being for both animals and humans. MOS is considered a natural nutritional supplement offering a novel approach to support the microflora and thus improve overall health and well-being.

In food animals, gut health plays an additional role. A healthy gut enables more efficient use of feed, thus improving feed efficiency. One particular potentially important function for MOS, based on the previous description is a possible replacement for fed antibiotics. As we have discussed here, for years antibiotic drugs have been added to the diets of food animals at non-therapeutic levels in the absence of disease, in order to enhance the feed conversion ratio, accelerate growth and protect the animal's health, therefore increasing profitability for producers. With the current global push to reduce the use of medically important antibiotics as feed additives for farm animals, there is significant interest in “natural” nutritional concepts. Based on a large body of research MOS has established itself as a one of the more important natural additives in food animal production.

The first trial ever reported with MOS was with young bull calves. Newman and co-workers reported improved feed intake and better growth rates. The health status of young calves is one of the most important factors contributing to growth and performance. Diarrhea in young calves is a major issue in the dairy sector. In many cases, an E.coli infection of the intestine is often involved. As MOS can bind E. coli, it can modify and help to improve the composition of the intestinal microflora. This resulted in a reduction in fecal E. coli counts and improvements in fecal scores in calves fed MOS. These improvements were coupled with an increase in concentrate (dry feed) intake and better performance. In addition to the changes in the gut, several workers also noticed improvements in respiratory health, which can also contribute to better performance. Conversely, one trial reported no effects on liveweight gain despite increased feed intake. Higher live weight gain, similar to that gained with the use of antibiotics, has been achieved following supplementation of milk replacer with MOS.

Mature dairy cows fed MOS had better immune protection against rotavirus and were able to pass some of this protection on to their calves. The transfer of immunity from the cow to the calves is critical in order to protect the calf from many different diseases. It can be assumed, therefore that since these positive effects can also be noted in beef cows and calves.

Beta-glucans (β -glucans)

Beta-glucans are major structural components of the cell wall of yeast, fungi and some cereals such as barley and oats. β-Glucans are similar to and in many case confused with MOS. They are significantly different and function in the body differently. Whereas MOS is based on the mannose sugar molecule, β-glucans are combinations of glucose molecules characterized by specific linkages. β-glucans are a diverse group of molecules that can vary with respect to molecular mass, solubility, viscosity, and three-dimensional configuration. They occur most commonly as cellulose in plants, the bran of cereal grains, the cell wall of baker's yeast, certain fungi, mushrooms and bacteria.

β -glucans derived from yeast and medicinal mushroom are notable for their ability to have a positive effect on the immune system. Of these β-glucans, those from yeast cells are the most common. You may also see different designations of β-glucans on the market. Those strains identified as an insoluble “(1,3/1,6) β-glucan”, has greater biological activity than that of its soluble “(1,3/1,4) β-glucan” counterparts. The differences between β-glucan linkages and chemical structure are important in regards to solubility, mode of action, and overall biological activity.

One of the most common sources of (1,3) β-glucan for supplement use is derived from the cell wall of baker's yeast (Saccharomyces cerevisiae) as with MOS products. However, (1,3)(1,4) β-glucans are also extracted from the bran of some grains such as oats and barley, and to a lesser degree in rye and wheat. The (1,3) β-glucans from yeast are often insoluble as noted previously. Those extracted from grains tend to be both soluble and insoluble. Other sources include some types of seaweed,[2] and various species of mushrooms such as Reishi, Shiitake, and Maitake.[3]

β-glucans are known as "biological response modifiers" because of their ability to activate the immune system. They are also referred to as immunostimmulants. Immunologists at the University of Louisville discovered that a receptor on the surface of innate immune cells called Complement Receptors is responsible for binding to β-glucans, allowing the immune cells to recognize them as not part of the body. The use of immunostimulants, for enhancement of disease resistance to a wide spectrum of pathogens at times of stress, provides a strategy which can improve suboptimal immune function and thus increase resistance to infectious diseases. Over the years, many substances have been identified and studied for their immunostimulatory activities. However, most of them cannot be used in domestic food animals due to cost, toxicity, undesirable side effects, or safety concerns for the consumer. Research has shown beneficial effects on the stimulation of the immune system by compounds of microbial or plant origin such as, β-glucans, with the potential to minimize the incidence of disease in livestock.

As the industry moves closer to a serious restriction of various antibiotic compounds by which we currently support animal health and performance, alternatives must be identified. More research into the effectiveness of β-glucans in cattle feeding systems is necessary to determine how and to what level these compounds can be used as a replacement tool.


Both MOS and β-glucans are products of interest for the livestock feeding industry. In many cases to get true efficacy we need to identify the best case feeding scenarios where these products can have the most affect. Plus, we need to examine combination of these and other tools to determine where synergisms might lie to enhance animal performance.

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, TX. He can be reached at sblez@verizon.net or at (903) 352-3475. For more information please visit us on at www.facebook/reveille livestock concepts.

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