Direct Fed Microbial: Application and Usage
Direct-fed microbials (DFM) were originally called probiotics until 1989 when the Food and Drug Administration (FDA) required manufacturers to use the term "direct-fed microbials." The FDA defines DFMs as "a source of live (viable), naturally occurring microorganisms." FDA does not allow companies selling DFM products to make therapeutic claims, which includes the following:
The exception to these "claims" is the approval of a new animal drug application. Table 1 lists FDA and Association of American Feed Control Officials (AAFCO) approved microbial species for use in DFM products.
Bacillus - Unique, gram-positive rods that form spores. These spores are very stable and can withstand environmental conditions such as heat, moisture, and a range of pH. These spores germinate into active vegetative cells when ingested by the animal and can be used in meal and pelleted diets.
Lactic Acid Bacteria - Gram-positive cocci or rods that produce lactic acid, which are antagonistic to pathogens. Since lactic acid bacteria appear to be somewhat heat-sensitive, they are not normally used in pelleted diets. Types of lactic acid bacteria include:
Yeasts - Not bacteria. These microorganisms belong to the plant group fungi. Six different types of dried yeast products are defined by the AAFCO as ingredients for animal feeding (Table 2).
The concept of DFMs began in the 1950s when researchers observed a positive growth response in animals fed antibiotics. This led scientists to theorize that intestinal microflora play an important role in the growth of animals. Further research determined a healthy intestinal tract consists of microflora in a delicate balance between two general types of microorganisms, beneficial and potentially pathogenic.
The coexistence of beneficial and potentially pathogenic bacteria is an important factor in the general health of an animal. If this balance is upset, the number of beneficial bacteria could decline while the number of potentially pathogenic bacteria could increase, compromising the animal's health and growth potential. Feeding DFMs containing live, beneficial bacteria can help to maintain this balance, which may help optimize animal health and growth performance.
Proposed DFM Modes of Action
DFM Forms and Usage
DFMs are available in a variety of product forms including powder, paste, gel, bolus, and capsules. They may be mixed in feed, top-dressed, given as a paste, or mixed into the drinking water or milk replacer. Usage directions vary from single-dose to continuous feeding.
A number of DFM products are currently available. Most DFMs contain live bacteria; however, some contain only bacterial or fungal extracts or fermentation byproducts. According to AAFCO, "fermentation product" indicates the product contains microbial cells, while "fermentation extract" indicates the product contains enzymes extracted from a microbial fermentation (cells are not contained in the product).
The effectiveness of DFMs depends on when they are used. The addition of DFMs to an animal's diet can assist in the replenishment of beneficial bacteria, resulting in a quicker return to balanced intestinal microflora. The best response can be observed during the following situations:
Handling and Storage
The stability of live DFMs is critical because the microorganisms must be delivered live to the animal to be effective. Therefore, it is important to follow the manufacturer's storage and handling recommendations. Most DFMs require storage in a cool, dry area, away from heat, direct sunlight, and high levels of humidity. After opening, the unused portion should be kept tightly closed to protect the DFMs from loss of viability.
Units of Measure for Bacteria and Yeasts
True, live-organism DFM products must provide a guaranteed number of live microorganisms present that can be substantiated using laboratory techniques. Unfortunately, the results often depend on how the product sample was originally obtained and handled and the testing lab's counting methodology. Therefore, because there is no standardized format, minor differences in technique can dramatically affect final results.
The most common enumeration methods are viable plate count and direct microscopic count. The viable count is based on the assumption that a single, viable microorganism will grow into one colony in a growth medium. A series of dilutions are made and dispensed into a petri dish. After incubation, the number of colonies are counted and multiplied by a dilution factor, giving the number of viable colony forming units (CFU) per gram of product. In the direct microscopic count, the number of bacteria on a grid are counted under a microscope. A total count of bacteria is reported, because dead and live cells cannot be distinguished.
Although some uncertainty exists,
enough evidence is available to warrant consideration for the use
of a DFM in the feeding of various classes of livestock. Animals
that have been stressed seem to respond better to DFM
supplementation compared to healthy, non-stressed animals.
Therefore, DFM supplementation may have greater application during
stressful conditions, such as during parturition and lactation,
for neonatal animals, and during disease or environmental
challenges. The use of DFMs in animal nutrition will most likely
continue to increase. As our understanding of this emerging
technology increases, ADM Alliance Nutrition will make appropriate
program changes to enhance swine productivity and efficiency.
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ADM Alliance Nutrition, Inc. , a wholly owned subsidiary of the Archer Daniels Midland Company