Dairy Quality University DIRECT-FED MICROBIALS AND FUNGAL ADDITIVES FOR DAIRY CATTLE

Improved animal health and performance always has been the goal of people associated with livestock production. Consequently, any feedstuff, feed additive, drug or other compound that is capable of enhancing animal health or performance will interest producers, veterinarians, and animal nutritionists. Several compounds have been used to improve animal performance either by manipulation of the rumen environment (e.g., sodium bicarbonate) or by directly altering the composition and metabolic activities of rumen microorganisms (e.g., ionophores).

More recently, growing concern over the use of antibiotics and other growth stimulants in animal feeds, the potential risk of antibiotic residues appearing in meat and milk, and the need for a food supply that is perceived as safe by consumers, has prompted many livestock producers to explore alternative strategies to enhance the overall health and performance of their herd or flock. Direct-fed microbials (DFM), or probiotics as they traditionally have been called, is one such naturally-occurring product that has been incorporated into livestock diets in an attempt to accomplish this objective. DFM, particularly yeast cultures, stimulate growth of rumen bacteria in contrast to ionophores and antibiotics which are toxic to selective bacteria. Although the total microbial population is increased with DFM supplementation, the cellulolytic and lactic acid utilizing bacteria are stimulated preferentially. Other yeasts and yeast cultures, such as brewers yeast, have been used as supplements in animal feeds for years, primarily due to their high protein and vitamin content.

Terminology
The term probiotic, derived from the Greek meaning "for life," was used initially to describe substances produced by one protozoan which stimulated the growth of another. More recently, probiotics have been defined as "a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance." Thus, they are the opposite of antibiotics, which were developed to inhibit microbial growth. In an effort to clarify confusion in terminology, the Food and Drug Administration (FDA) in 1989 adopted the term direct-fed microbials to refer to "a source of live (viable), naturally occurring microorganisms," which includes bacteria, fungi, and yeasts. FDA has accepted 42 organisms as generally accepted as safe (GRAS) and as being appropriate for use in animal feeds. Each of these organisms are naturally occurring bacteria from the gut of normal, healthy animals, and are not genetically engineered. They are the same genus and species as those used in human foods and are not toxic to humans or to animals.

A multitude of claims have been made for various DFM products and combinations.

  1. Improved growth rates by suppression of clinical infections.
  2. Improved utilization of feed by promoting digestion of previously indigestible feedstuffs or by increasing the efficiency of existing digestive processes.
  3. Improved milk production by dairy cows.
  4. Increased egg production.
  5. Improved animal health by stimulation of the immune system, or increasing the resistance to infectious diseases by direct antagonism.

Unfortunately, the evidence to support these claims often is variable and inconsistent. To be effective, a DFM should meet the following criteria:
  1. Be a strain capable of exerting a beneficial effect on the host animal.
  2. Be non-pathogenic and non-toxic.
  3. Be present as viable cells, preferably in large numbers, although minimum effective dose is unknown.
  4. Be capable of surviving and metabolizing in the gut environment, e.g., resistant to low pH, organic acids, bile salts, and digestive enzymes.
  5. Be stable and capable of remaining viable for long periods under storage and field conditions.

Role of Stress
Many of the proposed benefits from feeding DFMs are related either directly of indirectly to stress. Unfortunately, stress is an often used, yet poorly defined term. An animal can be stressed as a result of any of the following causes:
  1. Nutritional
    1. deficiency of a nutrient, e.g., underfeeding protein
    2. excess of a nutrient, e.g., ammonia toxicity due to excess protein
    3. antagonism between levels of two or more nutrients
  2. Environmental
    1. thermal, e.g., heat, cold, wind, rapidly changing temperatures
    2. moisture, e.g., rain or mud
    3. crowding
    4. sanitary conditions, e.g., manure accumulation
  3. Emotional
    1. handling or shipping
    2. changes in pen-mates
    3. weaning
  4. Disease
    1. infectious
    2. metabolic, e.g., milk fever or ketosis

When an animal is stressed, there is a change in the intestinal microflora. Often this is characterized by an increase in the number of coliform and other enterotoxigenic bacteria. Thus, the anticipated response to DFM would be greatest in animals following a stressful period when the animal's need for re-establishment of a normal gut microfloral is greatest.

DFM for young ruminants
Most of the research on the effects of DFM in young ruminants has involved the addition of various lactic acid producing bacteria, primarily Lactobacillus and Streptococcus, as intestinal inoculants to suppress neonatal diarrhea, and to improve the growth rate of young or stressed calves. The primary action of DFM appears to be related to enhanced development of rumen function by minimizing growth of pathogenic bacteria, increasing desirable microbial populations in the gut, and facilitating fiber digestion. Live bacteria are required for these processes to occur, meaning the organisms must be capable of surviving processing, remain viable during storage, tolerate the low pH found in the stomach, and then colonize in the gut. While the mechanism by which growth of undesirable pathogens is retarded remains uncertain, several potential modes of action have been proposed to explain the observations.
  1. Production of organic acids, hydrogen peroxide, and/or antibiotics could destroy undesirable microorganisms.
  2. Lowering the oxidation/reduction potential could limit oxygen availability to pathogens.
  3. Production of beneficial enzymes could improve nutrient availability.
  4. Detoxification of harmful metabolites could improve animal health.
  5. Displacement of enterotoxigenic organisms, such as E. Coli from the gut wall through competitive inhibition for attachment, adhesion, or colonization sites in the digestive tract.
  6. Improved microvilli health/nutrient uptake.
  7. Act as an immunomodulator by stimulating a local immune response in the gut.
  8. Production of B vitamins.
  9. Reproduction in ammonia and amine produced.
  10. Production of lactic acid.

DFM for adult ruminants
There is a tremendous amount of skepticism surrounding the use of DFM in adult ruminant diets. This doubt is the result of early 'probiotics' that simply did not work, only a few research trials published (which reported inconsistent responses to DFMs), and overzealous marketing by some commercial interests. A lot has changed in the last ten years. More recent research and development efforts have identified specific microbial strains that stimulate ruminal bacteria more than others, and these have been selected and targeted for use with particular diets to enhance production of either meat or milk.

Most research with lactating dairy cows has involved dietary supplementation with either Aspergillus oryzae (amold that is classified as a fungus) or Saccharomyces cervisiae (a yeast that is classified as a fungus). Aspergillus oryzae is a fermentation extract produced from a selected strain of enzyme producing Aspergillus oryzae and is marketed by a variety of companies. It has its main effect in the rumen,increasing the population of cellulolytic bacteria, shifting VFA fermentation patterns by a reduction in the proportion of propionate relative to acetate and an increase in butyrate, and stabilizing rumen pH.

Saccharomyces cervisiae is marketed as a yeast culture, which contains both viable yeast cells and a dried preparation of the media in which those cells were grown. It is dried so as to preserve the fermenting capacity of the yeast. Feeding Saccharomyces cervisiae tends to result in a reduction in rumen ammonia levels, implying increased growth of rumen bacteria.

Results of numerous studies with DFM being added to the diets of lactating dairy cows are variable and inconsistent. There were significant increases in dry matter intake, milk production, milk fat percentage, and milk protein percentage in some, but not all trials. The cause of the variable response is still undetermined and may be related to the variety of DFM strains contained in the preparations fed. More research is needed to clarify the mode of action for these products and to identify specific strains that function best with different types of diets (level of non-structural carbohydrates, amount of degradable versus undegradable protein, type and quality of forage, etc.) and animal requirements.

There appears to be a relationship between the effectiveness of the DFM in eliciting a response, and the diet and nutritional demands of the animal. The response to yeast culture appears to be greater when supplemented to lactating cows in early lactation as opposed to cows in mid- or late-lactation. The response in milk yield increases as the ration of forage to concentrate in the diet decreases.

Summary
The specific role for many DFMs has not been defined. Animals that have been stressed have a greater response to DFM supplementation than do normal, healthy animals. Thus, until more information is available regarding specific applications, the primary role for supplemental DFM would be following periods of high stress, such as:
  1. neonatal calves
  2. post weaning
  3. following shipping
  4. during periods of heat stress
  5. during the early postpartum period
  6. following metabolic disorders

Additional research is needed to evaluate the relationship between diet type animal response, and economic response.

Reprinted with permission from DIRECT FED MICROBIALS AND FUNGAL ADDITIVES FOR DAIRY CATTLE, by Lee Kilmer, Department of Animal Science, Iowa State University.