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In the first installment of this series we began a discussion of feed additives that can contribute to animal health and performance. As discussed there are a variety of feed additives which, one day, may be called upon to take up the role vacated by antibiotics as they are forced out of the industry. Fortunately there are a wide variety of tools available, which when used properly can enhance the performance of the immune system, improve the digestive process or cause metabolic changes in the animal that improve efficiencies.

In the previous installment we started with enzymes. Enzymes are used more extensively in monogastrics (pigs and poultry) and are still in early stages of use in cattle. Data has shown the ability for fed enzymes to improve fiber and starch digestibility in ruminants. But as with a lot of nutritional research there have been a lot of variation in results.

Direct Fed Microbials

Another type of feed additive, that have been used for years in beef cattle programs are direct fed microbials (DFMs). Direct fed microbials are cultures of bacteria, yeasts or fungi that have shown to be useful in enhancing digestive performance at different points within the gastrointestinal system. For cattle, being ruminants, this may extend from the rumen system (rumen, reticulum, omasum, abomasum) through the small and large intestines. However, the predominant target areas are the rumen and the small intestine. The actual applications in cattle have varied a bit over the years. Bacterial cultures have been used for quite some time in feedlot cattle as a means of overcoming stress, reducing the incidence of digestive upset, predominantly bloat and acidosis and as a competitive inhibitor of pathogens such as E. coli O157:H7. Similar cultures have been used in young calves in an effort to reduce gut inflammation and reduce the colonization of the immature digestive tract by pathogenic organism which might cause an increase in scouring and dehydration. More recently, research has shown fed bacterial cultures to have benefits in lactating dairy cows. Yeast cultures have been used for years in most classes of cattle for a variety of purposes. Generally they have been shown to improve ruminal function, reduce stress effects and help improve dry matter intake. Finally, several strains of fungi have also been fed for their beneficial effects, much of which is related to improvements in fiber digestion.

Some Background

Before birth, the developing fetus is sterile in the uterus of the dam. At birth, the digestive tracts of all animals begin a natural colonization by a wide assortment of microorganisms. We see this process started in cattle as the cow begins to lick the calf, especially around the muzzle (mouth and nose). Under healthy, non-stressful conditions, �beneficial� microorganisms multiply in the rumen and the intestine in a symbiotic relationship with the host animal. Beneficial rumen and intestinal microbes supply nutrients to the animal, aid in digestion of dietary nutrients, and compete with potential pathogens. As a contrast, research has shown that when young animals are removed and raised under sterile conditions, the microorganisms that are normally accumulated from the environment are prevented from colonizing their digestive tracts. These animals often have increased nutritional needs and abnormal immune responses. For example, various strains of bacteria in the rumen produce most of the B-Vitamins required by cattle. Calves raised under sterile conditions typically require B-Vitamins to be fed or supplemented to meet their requirements. Sterile animals also are more susceptible to bacterial infections, presumably due to rapid establishment of pathogens. This helps illustrate the true need ruminants (as well as all animals) have for these organisms as part of their normal physiological function.

Originally, cattle were fed large amounts of "beneficial" microbes, primarily bacteria when they were believed to be stressed. These periods would include after long distance transportation, dietary changes, health or environmental challenges, etc. It was believed that this practice would help prevent the establishment of pathogenic bacteria and could help re-establish normal gut microflora. This practice originated the term �probiotic� which means �for life.� While the term probiotic is still commonly used to describe these products, the term direct-fed microbial (DFM) is now more commonly used for microbial-based feed additive. These products may be sold without regulatory intervention by the FDA or USDA as long as health or production claims are not made.

A fairly common theory that may help explain how DFMs function to improve animal performance is that the addition of beneficial bacteria exclude the establishment of pathogens. This is also known as �competitive exclusion.� Production of antimicrobial end products such as acids and antibiotics and other unidentified co-factors has also been suggested. The following is a list of other potential effects positively influencing animal performance:

� Stimulation of other beneficial microorganisms

� Production and/or stimulation of enzymes

� Metabolism and detoxification of undesirable compounds

� Stimulation of immune response in the host animal.

Bacterial Cultures

In general, most feed industry and animal production microbiologists would agree that DFMs based on a bacterial culture must be alive when the culture is fed. Thus, they must survive processing, storage, addition to the feed and feed mixing and finally the gut environment to the target location. Some researchers have suggested that it is not the actual bacteria themselves that are the benefiting factor but end products such as bacteriocins which are narrow spectrum antimicrobial substances produced by the bacteria.

The most commonly fed DFMs are Lactobacillus acidophilus (and other Lactobacillus species), L. casei, Enterococcus diacetylactis, Propionibacterium freudenreichii, and Bacillus subtilis. In cattle, much of the research in feeding bacterial based DFMs has involved feeding lactobacillus-based DFM to young calves fed milk, calves being weaned, or cattle shipped to the feedyard because these conditions were often classified as times of high stress. Calves fed L. acidophilus have been reported to have reduced incidence of diarrhea and reduced counts of intestinal coliform bacteria. Earlier feeding data, while variable, reported improved growth performance. Incoming feedlot cattle showed an advantage of 10.7 and 5.4 percent in average daily gain and feed efficiency, respectively, for cattle fed a bacteria-based DFM. Later studies have not shown improvements to this degree although improved performance has been reported.

Microbiologists have continued to work to understand the effects DFMs can have in cattle feeding scenarios. For instance, Megasphaera elsdenii (ME) is the major lactate-utilizing organism in the rumen of adapted cattle fed high grain diets. However, when cattle are abruptly shifted from a high-forage to high-concentrate diet, the numbers of ME are often inadequate to prevent lactic acidosis, a common ruminal condition as a result of the rapid digestion of high grain/starch diets. Research has shown that during a challenge with highly fermentable carbohydrates (starch), addition of Megasphaera elsdenii B159 prevented an accumulation of lactic acid and shifted ruminal fermentation beneficially. Addition of ME has also experimentally prevented acidosis in feedlot steers. More recent research has continued to explore the effects of ME on reducing excessive levels of lactic acid in cattle on high grain diets with favorable results.

Bacterial cultures have likewise been fed to pre-weaned and weaned calves in an effort to reduce the effects of weaning stress and to assist with getting newly weaned calves onto feed. Bacteria are seldom fed to beef cows simply because there are predominantly on high forage diets (pasture or hay) or because they are seldom fed or supplemented in a manner that allows for the inclusion of a live bacterial culture. Given current environmental issues many areas of the country have experienced and the stress these cattle are under, hand feeding has often become more common. If conditions are right, it could be of use to provide a bacterial culture to the cow herd to help overcome stress effects.

Yeast Cultures

Feeding of yeast to most classes of cattle has been common for years. A variety of mechanisms have been suggested to explain changes in the activity of the rumen and improvements in performance when ruminants are fed yeast-based DFMs. For example, yeast may have a buffering effect in the rumen by mediating the sharp drops in rumen pH, which follows feeding of higher concentrate rations. As such, yeast may help to buffer excess lactic acid production when ruminants are fed high concentrate diets. The effects on buffering are not extensive; as added yeast cannot prevent lactic acidosis if the rumen is challenged with a ration high in fermentable carbohydrates (grains, starch).

At higher pH levels, however, when feeding yeast, research has found increased numbers of rumen cellulolytic (cellulose digesting) bacteria and improvements in fiber digestion. One of the most common types of yeast fed, Saccharomyces cerevisiae has been shown to stimulate the growth and activity of rumen bacteria. The response has different somewhat depending on the exact strain of the yeast, which are numerous. Some strains of yeast appear to produce certain enzymes which may improve fiber digestion. While a number of other potential effects have been reported, the research, as with all DFM research has been somewhat varied and dependent upon the exact application. It is thought, however, that the effects of feeding yeast to cattle are found predominantly in the rumen with very little effect in the lower gut.

There has also been some debate on exactly what and how much of a given yeast-based DFM needs to be fed by the producer. Some products on the market guarantee high numbers of live yeast cells (e.g., 1 x 109cfu per g) with low recommended feeding rates (only 10-20 grams per day). Other products suggest that live organisms are not required for beneficial effects and that the end products (metabolites produced by the yeast cells) are the �active� ingredients. Both types of yeast product have been reported to produce a variety of positive effects especially when fed to animals on a high forage diet. To a large degree feeding of yeast has become the norm for lactating dairy cows. Other fairly common applications have been to weaning and transition cattle and inclusion in free-choice minerals which can help improve product palatability. Feeding of yeast to finishing cattle has been less common although there is some data available which suggest that yeast feeding has shown to improve feed efficiency. As suggested earlier, it may play a positive role in helping stabilize rumen activity in cattle on high grain diets. However, bacterial products seem to be more commonly used in feedlot programs than yeast products.

Fungal DFMs

While yeasts may also be considered a fungal product, for the purposes of this paper fungal products have been differentiated from yeast products. One such fungal DFM is Aspergillus oryzae (AO) which has been used in a number of applications, largely to improve fiber digestion. Research with AO has been more common in dairy cattle than other classes and earlier work seemed to suggest that the greatest responses have been in dairy cows early in lactation that are fed higher energy (higher grain) rations.

However, more recently AO research has focused on its potential to assist with improving fiber digestion. Some work has shown that feeding OA to beef cows helped improve the digestion and subsequent nutrient availability when feed poorer quality forages. Also, some research has shown a potential to increase average daily gain in feedlot cattle fed AO under certain circumstances due mainly to an improvement in dry matter intake.

� Reported positive effects from feeding AO include:

� Improvement in rate and extent of fiber digestions

� Improved microbial protein yield from the rumen

� Increased lactic acid uptake (rumen pH stabilization)

� Increase volatile fatty acid production in the rumen (predominant source of energy for cattle)

� Reduction in heat stress

Practical Considerations for DFMs

Direct-fed microbial products are available in a variety of forms including powders, pastes, boluses, and capsules. In some applications, DFM may be mixed with feed or administered in the drinking water. However, use of DFM in drinking water must be managed closely since interactions with chlorine, water temperature, minerals, flow rate, and antibiotics can affect the viability of many organisms. Bacterial DFM pastes are formulated with vegetable oil and inert gelling ingredients. Some fungal products are formulated with grain by-products as carriers.

Some DFM are designed for one-time dosing while other products are designed for feeding on a daily basis. Since the recommended feeding method of some strains (especially bacteria) is that it must be fed in a �live� form it is typically packaged freeze-dried in foil pouches. These are best kept cool and opened at the time of feeding. As such this creates some logistical issues for some producers. Yeasts and fungal products are commonly available in a dry form in50 lb or 25 kg bags. As such they can be less challenging to handle. In all cases, the feeding rate is generally quite small so thorough mixing is critical.

Regulatory Status of DFM

While DFMs have shown a wide range of benefits when fed to cattle the ability for the manufacturers to promote these benefits is carefully monitored. Food and Drug Administration have set forth guidelines to regulate sales and claims of DFM products. Producers and sellers of DFM products, by law, cannot make therapeutic claims, cannot claim to establish viable bacterial colonies in the gut, and cannot claim to affect structure or function of the animal. At this time, DFM products cannot claim to decrease morbidity, reduce sick days, or increase milk production, affect growth or feed intake without a new animal drug application.

Conclusions

Use of DFMs in most classes of cattle feeding and supplementation programs show a great deal of promise. In many cases the actual product to be used is very dependent on the application so it is important that the producer carefully researches the products to determine which is the best fit for his program. Your nutritionist can also be helpful in determining which product will work the best in a given application.

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

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