Use of Direct-Fed Microbials in Farm Animals

According to the FDA (Fuller, 1999), DFMs that have been included in food for many years without any adverse effects are GRAS and have been shown to have beneficial effects in the animal (Fuller, 1989 Juven et al, 1991 Lee et al., 1999). The concept of DFMs is now universally accepted, and a substantial amount of research is being directed toward formulation of mixtures of DFM strains that would have potential beneficial effects in the animal, including improvement of animal performance and inhibition of food-borne pathogens. 

Since the first scientific explanation of the favorable effects of soured milk products in humans by Metchnikoff (1907) at the beginning of the twentieth century, the most beneficial part of the intestinal flora is suggested to be LAB. LAB are also the most common organisms used for commercial DFM preparations (Anonymous, 1990 Tuschy, 1986). The emphasis on the LAB stems from evidence that LAB play a central role in the gut flora that enables them to influence the composition of the flora to the benefits of the host. The stomach of the neonatal pigs is shown to be colonized by Lactobacillus and Streptococci within 48 hours after birth (Dulcuzeau, 1985). Similarly, in newborn calves one of the first groups of microorganisms in the rumen is LAB (Nousiainen and Setala, 1993). Studies show that when the gut flora develops after birth, as the lactobacilli increase, other components of the flora decrease (Smith, 1965). The claims made for DFM effects of LAB in farm animals are many and varied. 

The potential benefits of DFM LAB can be placed into three broad categories (1) reduction of food-borne pathogens, (2) improved animal performance, and (3) stimulation of immune response. Reduction of food-borne pathogens in the live animal to prevent subsequent contamination of the food supply is the focus of this discussion. 

The most commonly identified beneficial effect of LAB as live feed supplements is their role in resistance to infection, particularly in the GI tract. It has been proposed that these organisms can prevent infection through competitive exclusion (CE) or other mechanisms against pathogenic bacteria in the animal intestine (Bailey, 1987 Pivnick and Nurmi, 1982). According to Bailey (1987), competitive exclusion implies the prevention of entry of 

The GI tract of poultry is complex. A newly hatched chick will become colonized rapidly with facultative aerobes, but lactobacilli will eventually become the primary organisms present in the crop and small intestine of the chick (Fuller, 1992). Modern poultry production prevents contact of the chick with the parent. Therefore, DFMs have been administered soon after hatching to increase the likelihood of the organisms in the DFM to become a part of the natural microflora of the bird. More research has been done in the area of DFM and inhibition in poultry than in any other species. 

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