Larry Roth, Ph.D.

A healthy and beautiful horse is the pride of every horse owner. Feeding selected cultures of lactic acid-producing bacteria and yeast boosts horse health and performance, according to many owners. Understanding the benefits of direct-fed microbial cultures can help you decide when to use these products during your horse’s life cycle.

In 1908, the Russian biologist Eli Metchnikoff credited the long lives of certain Bulgarian and Russian citizens to the consumption of large amounts of fermented milk products (4). The key organism in these foods was later identified as Lactobacillus acidophilus, a lactic acid-producing bacteria (10).

The lactic acid-producing bacteria are so named for their ability to produce lactate. However, lactate production is only one of many benefits derived from this collection of bacteria. The lactic acid-producing bacteria most frequently featured in direct-fed microbial products include Lactobacillus acidophilus, Enterococcus (or Streptococcus) faecium and Lactobacillus lactis.

For many centuries, people have observed that their animals were healthier when fed feedstuffs resulting from yeast fermentation. Yeast are fungi, or one-cell organisms that reproduce by budding, or producing daughter cells. The yeast species most utilized by the direct-fed microbial industry are Saccharomyces cerevisiae and Aspergillus oryzae.

Based on the work of Metchnikoff and others, the idea was developed to directly feed live, lactic acid-producing bacteria and yeast to animals for improving their health and performance. The observed benefits may result from: 1) competition for attachment sites in the digestive tract, 2) competition for essential nutrients, 3) production of antimicrobial substances, 4) increasing the growth of beneficial bacteria and 5) stimulating the immune system (8).

Competition For Attachment Sites In The Digestive Tract

Some disease-causing bacteria reduce an animal’s ability to absorb nutrients by disrupting the small intestine (8). Lactic acid-producing bacteria attach to the lining of the small intestine and produce a substance to prevent disease-causing organisms from binding to the intestinal wall (7). The attachment of the beneficial bacteria may increase the absorptive surface area of the small intestine and enhance enzyme activity for greater nutrient absorption by the animal (8, 11).

Competition for Essential Nutrients

Lactic acid-producing and disease-causing bacteria require certain nutrients for growth. The beneficial bacteria could utilize vitamins, amino acids or other nutrients that might otherwise support the growth of harmful bacteria (5).

Production Of Antimicrobial Substances

The ability of direct-fed microbial cultures to inhibit disease-causing organisms is of considerable interest. Lactic acid lowers the intestinal pH to create an environment unsuitable for harmful organisms (8). Lactic acid-producing bacteria secrete hydrogen peroxide, resulting in conditions unfavorable for oxygen-requiring microorganisms (2).

Bacteria produce bacteriocins that restrict the growth of other microorganisms, often genetically related species (8). The lactic acid-producing bacteria have demonstrated the ability to inhibit E. coli, Salmonella typhirium, Staphylococcus aureus and Clostridium perfringens (5). The reduction of scour-causing organisms is especially important in new-born and young animals.

Increasing The Growth Of Beneficial Bacteria

Enhancing the growth of beneficial bacteria boosts the performance of healthy animals. The B-vitamins, enzymes and other factors secreted by lactic acid-producing bacteria and yeast stimulate starch- and fiber-digesting bacteria (3, 5). The ability of yeast to enhance fiber digestion could allow dietary changes (12). The ability of yeast to increase feed intake has been recognized for centuries.

Stimulating The Immune System

Recent advances in animal health indicate the importance of proper immune function. Research indicates that lactic acid-producing bacteria heighten immune function at the digestive tract and whole-system levels (6). Experiments with bacteria-free extracts from lactic acid-producing cultures demonstrate improved macrophage activity against E. coli (9) and Salmonella typhirium (1). The role of direct-fed microbial cultures in stimulating the immune system warrants further research.

The Use Of Direct-fed Microbial Products With Foals

Although foals are born with bacteria-free digestive tracts, the tract is quickly populated by disease-causing and health-promoting bacteria. The question becomes, "Which type of bacteria will dominate?" Providing direct-fed microbial cultures shortly after birth can favor the beneficial bacteria. Studies suggest that lactic acid-producing bacteria inhibit scour-causing microorganisms, and can aid in the absorption of nutrients.

Microbial gels and pastes are available for oral delivery to foals, or dry cultures can be mixed with milk replacers.

The Use Of Direct-fed Microbial Products With Growing And Mature Horses

Diet changes and other challenges at weaning can alter a foal’s nutrient intake and health status. Controlling harmful bacteria in the digestive tract during variable feed intake is very important. The microbial gel and paste products can be placed directly in the foal’s mouth, and the owner can confidently know that an animal with low or no feed consumption received the intended microbial dose. Dry products can be mixed with the feed for daily maintenance.

Yeast cultures aid in stabilizing the microbial balance in the digestive tract, which may reduce the problems resulting from grain over-consumption and colic. In addition, yeast stimulates fiber-digesting bacteria to increase the energy a horse derives from forages.

Consequently, the ration composition could shift in favor of forages over grains, increasing the safety of the horse’s diet. Always consult your veterinarian or nutritionist before making dietary changes.

Breeding, foaling, showing and heavy training can alter feed intake and increase a horse’s susceptibility to disease-causing organisms. Restoring nutrient intake, stabilizing the balance of digestive tract bacteria and proper immune function become critical during these challenging periods. Many horse owners suggest that direct-fed microbial cultures can play a major role during these critical periods. In addition, improving the nutritional status of the horse enhances the hair coat and durability of the hooves. The oral and feed products used for younger horses work equally well with mature horses, although the amount of lactic acid-producing bacteria and yeast should be increased.

Direct-fed Microbial Products And Storage

Direct-fed microbial products are available that feature only lactic acid-bacteria or yeast, and others include bacteria and yeast combinations. Microbial gels and pastes are placed between the lower teeth and cheek of the horse. Certain dry powders are dispersible in milk replacers and liquid feeds. Other dry products are readily mixed in the feed. However, always be sure to purchase reputable products handled properly by the manufacturer and seller. The direct-fed microbial products should be stored incool, dry locations to maintain their microbial viability.

Feedstuffs resulting from microbial fermentation have benefited animals and their owners for many centuries. Continuing research projects document the need to include direct-fed microbial products in horse management programs. Many horse owners have experienced the benefits of directly feeding live bacteria and yeast to their animals._______

Larry Roth, Ph.D. is a research scientist with Conklin Co. Inc for the last ten years

551 Valley Park Dr.; Shakopee, MN 55379. Questions concerning direct-fed microbials and requests for the research references supporting the article should be directed to Dr. Roth.

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