Cattle Today

Cattle Today

cattle today (10630 bytes)

by: Stephen B. Blezinger
Ph.D., PAS

Part 1

The cattle producer has at his disposal numerous tools and management practices which can serve to improve the health, performance and productivity of his animals. These can include various medications and antibiotics such as Chlorotetracycline (CTC), ionophores such as Rumensin and Bovatec, a host of implants (Ralgro, Synovex, etc.), trace element compounds and vitamins of all sorts. One area that has gained a fair bit of press is that of the feeding of yeast cultures and direct-fed microbials (DFM's). These materials are typically fed with the intent of improving the digestive tract environment in order to reduce stress or improve the digestive process. Unfortunately for the producer, the use of these products has been variable and developing a good understanding and having confidence in the effectiveness of the product is difficult. This article and those to follow will provide a basis for understanding these products, how they work and how they are used. Much of the information here is based on a very good paper presented by Limin Kung with the University of Delaware at the 2001 12th Annual Florida Ruminant Nutrition Symposium.

The Basics

The use of feed additives containing live microorganisms and/or their metabolites (compounds they produce as waste) to improve the efficiency of production in cattle has increased, to a large degree, as a response to consumer demand for more “natural” growth-promoting or efficiency enhancing substances. Yeast Products, direct fed microbials, probiotics and other terms are used to identify a host of products that are based on populations of microbial organisms be they yeasts, bacteria or fungi which are thought to have a beneficial role in the rumen or lower digestive tract. Subsequently the use of these materials has shown or is believed to have shown benefit by improving the digestion of various nutrients, especially forages in the bovine digestive system.

Some Background

Before birth, developing ruminant animals are sterile in the womb of their mothers. Upon birth, the digestive tracts of all animals are naturally colonized by a variety of microorganisms from the environment. Under healthy and non-stressful conditions, “beneficial” microorganisms colonize the rumen and lower gut in a symbiotic relationship with the host. Beneficial rumen and lower intestinal tract microorganisms supply nutrients to the host, aid in digestion of dietary nutrients, and compete with potential pathogenic microbes. Interestingly, when young animals are removed and raised under sterile conditions, microorganisms from the environment are prevented from colonizing their digestive tracts. These animals often have increased nutritional needs (e.g., requiring more vitamin K or other B-Vitamins in the diet) and abnormal immune responses. A normal, functional rumen does not develop in ruminants raised in sterile conditions. Animals without normal microbial flora also are more susceptible to bacterial infections, presumably due to rapid establishment of pathogenic organisms. This research has shown that microbial colonization of the digestive tract is necessary for normal development and well being of livestock.

Direct-fed Microbials

The original concept of feeding microorganisms to animals involved the administration of large amounts of "beneficial" microbes to livestock when they were “stressed.” During the early stages of this research, the theory was that feeding beneficial microorganisms would prevent the establishment of undesirable microorganisms or to re-establish normal gut microflora. This practice was termed "probiotic", or “for life.” However, the term “probiotic” implied that these products had a curative or therapeutic capacity. This is problematic in the U.S., claims such as decreased mortality, fewer sick days, or increased production cannot be made of any product unless the safety and efficacy of the product has been approved by government regulatory agencies. To overcome this requirement, the U.S. feed industry, in conjunction with the Food and Drug Administration and the United States Department of Agriculture, has since accepted the more generic term of “direct-fed microbial” (DFM) to describe microbial-based feed additives. In addition, a list of accepted microorganisms for use in animal feeds was developed. In the U.S., DFM's may be sold without approval as long as the microorganism appears on the approved list and no claims of improved health or production are made.

How do DFMs Work?

There have been several hypotheses put forth to explain the usefulness of DFM. One of the most common explanations for improved animal health or production suggests that the addition of beneficial bacteria prevent the colonization of pathogens in the lower gut by competing for space and nutrients. Production of antimicrobial end products such as acids and antibiotics has also been discussed. Some of the proposed mechanism for how DFMs work include:

•Production of antibacterial compounds (acids, antibiotics).

•Competition with undesirable organisms for space and/or nutrients in the digestive tract.

•Production of nutrients (e.g. amino acids, vitamins) or other growth factors which stimulate growth and reproduction of other microorganisms in the digestive tract.

•Production and/or stimulation of enzymes.

•Breakdown and/or detoxification of undesirable compounds

•Stimulation of the immune system in the host animal.

Bacterial DFM for Ruminants

The general concept of “inoculating” ruminants with beneficial microorganisms is not a new practice. Specifically, many producers and veterinarians have been inoculating sick ruminants (especially those that have been off feed) with rumen fluid from healthy animals in hopes of stimulating normal rumen function and improving dry matter intakes.

In contrast, there are many bacterial-based DFM that are sold for use in ruminant diets with more specific applications. These products often contain bacteria known as lactobacilli with Lactobacillus acidophilus being one of the most common microorganisms used. Other commonly used bacteria include various species of Bifidobacterium, Enterococcus, and Bacillus. Most bacterial-based DFM are probably beneficial because they have effects in the lower gut and not in the rumen. For example, Lactobacillus acidophilus produced lactic acid, which may lower the pH in small intestines to levels that inhibit the growth of pathogenic microbes. Early research with DFM in ruminants first involved applications for young calves fed milk, calves being weaned, or cattle being shipped. These animals were thought to be highly stressed or had a microbial gut ecosystem that was not fully mature. Young cattle have immature digestive tracts that are obviously more prone to upset by pathogenic bacteria. Cattle that are shipped are often on limited feed and water for prolonged periods of time during transit. During these periods microbial populations may decrease in numbers thus resulting in digestive tracts that are in less than optimal condition. Large doses of beneficial organisms were thought to re-colonize a stressed intestinal environment and return gut function to normal more quickly in scouring calves. Unfortunately the data supporting such claims have been inconclusive. For example, calves fed L. acidophilus have been reported to have reduced incidence of diarrhea and reduced counts of intestinal coliform bacteria (a detrimental organism). However, a lack of beneficial effects of feeding bacterial DFM to calves has been reported in other studies.

Only a few studies have documented positive effects of feeding bacterial DFM to lactating dairy cows. High producing cows in early lactation would be the best candidates for such products because these cows cannot consume enough energy as compared to their requirements and typically consume diets high in fermentable carbohydrates that sometimes leads to acidosis. Studies in 1988 and 1998 reported increased milk production from cows fed L. acidophilus. Supplementation of lactobacilli may be useful in the close-up dry period (30 days just prior to calving) of lactation when intake is depressed and animals are stressed.

Fungal DFM

Fungal DFM have been popular additions to ruminant diets for many years. In general, three types of additives are available. First, some products contain and guarantee “live” yeast and are based on various strains of Saccharomyces cerevisiae. Second, other additives contain Saccharomyces cerevisiae and culture extracts but makes no claim for live organisms. Third, there are fungal additives based on Aspergillus oryzae (AO) fermentation end products and also make no claim for supplying live microbes.

By comparison to most commercial bacterial-based DFM, fungal based-DFM appear to be beneficial due to changes in ruminal fermentation and there is no direct evidence that fungal extracts affects digestion or metabolism in the lower gut. Stimulation of various ruminal bacteria has been reported in many studies. The numbers of total ruminal anaerobic and cellulolytic bacteria have been increased when feeding fungal extracts. There are several possible reasons for improvements in ruminal fermentation via fungal DFM. For example, fungal DFM may improve ruminal fermentations by preventing the accumulation of excess lactic acid when ruminants are fed high concentrate diets. Extracts of Aspergillus oryzae have been shown to improve the uptake of lactic acid by the rumen lactate-utilizing bacteria. Similarly, another study in 1995 reported that Saccharomyces cerevisiae also was able to prevent the accumulation of lactic acid production by competing with Streptococcus bovis for glucose and by stimulating the uptake of lactic acid by Megasphaera elsdenii, possibly by supplying amino acids and vitamins. However, the effects on pH are small as feeding added yeast was unable to prevent acute episodes of lactic acidosis when the diets were high rich in fermentable carbohydrates (high starch or grain levels). Regardless of this finding, higher ruminal pH may be one reason for the finding of increased numbers of rumen cellulolytic bacteria and improvements in fiber digestion with fungal cultures.


Although some uncertainty exists, enough evidence exists to warrant consideration of the use of microbial products in the feeding of various classes of cattle. In the next issue we'll take a look at yeast feeding and what potential benefits may exist there for improved health and performance. Additionally we'll look at other considerations for feeding and utilization.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached at P. O. Box 653 Sulphur Springs, TX 75483, by phone at (903) 885-7992 or by e-mail at


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