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The meat industry has worked for years to combat the survival of E. coli O157:H7, Salmonella spp., Campylobacter spp., and other harmful bacteria on meat products by implementing strategies after harvest to reduce or eliminate such pathogens. Although these strategies have been successful in reducing the incidence of these pathogens, the likely reason for the presence of such pathogens on meat products is that these microorganisms are often transiently found in the gastrointestinal tract of livestock species (Meyer-Broseta et al., 2001; Jay et al., 2005). Thus, carcass contamination will likely continue to occur unless strategies are developed to reduce the presence of pathogenic bacteria in the animal itself.
The use of natural feed supplements, such as probiotics [otherwise know as direct-fed microbials (DFM)] and prebiotics, have been proposed as an alternative to antimicrobial use in livestock. These compounds have been shown by many researchers to selectively increase populations of beneficial microorganisms within the rumen which could potentially lead to improvements in animal performance similar to those seen by ionophores and other feed supplements. Additionally, through the stimulation of beneficial bacteria, these compounds may be able to reduce populations of pathogenic microorganisms by out competing pathogens for nutrients and places of attachment within the gastrointestinal tract.
The objective of this study was to evaluate the efficacy of two natural feed supplements to reduce the survival and subsequent shedding of E. coli O157:H7 and Salmonella spp. in fed cattle during finishing and immediately prior to harvest.
One hundred sixty-eight (168) crossbred beef steers, initially weighing 250 to 340 kg, were used in this study. The study was designed to examine the effects of two natural feed supplements
[Saccaromyces cervisiae boulardii CNCM 1079-Levucell SB (LEV), and Aspergillus oryzae- Amaferm® (AMF)] with two dietary energy sources [dry, whole-shelled corn (DWSC), or high-moisture corn (HMC)] on growth performance, carcass characteristics and the ability of these products to reduce fecal shedding of E. coli 0157:H7 and Salmonella spp. of fed cattle. In addition, two control groups were fed either HMC or DWSC with no feed supplements added.
Levucell SB is a feed supplement that contains the CNCM I-1079 strain of Saccharomyces cervisiae, ssp. boulardii (yeast) and may have the ability to prevent adhesion of these pathogens to tissue surfaces and facilitate the removal of these microorganisms from the gastrointestinal tract. Amaferm® is a feed supplement that may have the ability to act as a prebiotic in ruminant livestock. Amaferm® is a fermentation extract produced from a select strain of Aspergillus oryzae, which works to stimulate the number and activity of the endogenous microflora. Amaferm® may potentially impact the presence of pathogenic microorganism by increasing the number of competing beneficial bacteria along the gastrointestinal tract.
At the initiation of the study, recto-anal swabs (for baseline prevalence of E. coli O157:H7) and fecal grabs (for both E. coli O157:H7 and Salmonella spp. baseline prevalence) were obtained and analyzed for pathogen prevalence. Cattle were on feed approximately 150 days and fecal samples were obtained every two weeks during the finishing period. Fecal samples were analyzed for the prevalence of E. coli O157:H7 and Salmonella spp.
Cattle receiving high-moisture corn (HMC) showed an improvement in feed efficiency compared to those cattle being fed dry, whole-shelled corn (DWSC). The addition of LEV to the high concentrate corn-based diets fed in this study did not have an impact on growth performance of feedlot steers. However, addition of AMF to a high-concentrate diet composed of DWSC resulted in an improvement in feed efficiency. Neither of the feed additives, LEV or AMF, had an affect on carcass characteristics, nor did they reduce the incidence or apparent shedding of E. coli O157:H7.
No animals tested positive for Salmonella throughout the feeding period. A spike in the shedding of E. coli O157:H7 was seen approximately 6 weeks after the start of the trial. Differences in the shedding of E. coli O157:H7 by feedlot cattle were observed between the two corn sources fed in this study. Cattle being fed HMC appeared to have more resilience against infection of E. coli O157:H7. The percent of animals within a pen shedding E. coli O157:H7 for pens receiving HMC declined to levels near those seen prior to the peak; whereas, the average percent of cattle within a pen for those pens on the DWSC diet was greater for several weeks after the peak in shedding occurred. Additionally, steers fed HMC shed E. coli O157:H7 less frequently than steers fed DWSC, indicating that these animals were less susceptible to infection.
Neither of the feed additives, AMF or LEV, was found to be effective in reducing the shedding of E. coli O157:H7 in cattle being finished on high concentrate corn-based diets. However, the results of this study did provide evidence that cattle being finished on a high concentrate diet that utilizes high-moisture corn (HMC) may be more resilient and have a lower level of susceptibility to infection from E. coli O157:H7 than those cattle being finished on a high concentrate diet formulated with DWSC.