The times continue to change. Livestock producers more readily recognize their role as food producers. Moreover, they see and feel the effects of rising or falling consumer demand for their product. Issues that increasingly confront livestock producers today are about assuring the quality, safety, and security of the food products they produce.
The consumer worries about livestock production issues that may affect their own health. Because of the actions taken through various Quality Assurance programs, previous concerns about physical and chemical hazards originating on the farm have been addressed successfully. Now the concerns are increasingly about biological hazards. The consumers worry about mad-cow disease, antibiotic resistance, multi-drug resistant Salmonella, enterohemorrhagic E. coli (e.g. Escherichia coli O157:H7) and other food safety pathogens which ultimately affects demand for product and the producers bottom-line.
For their part, producers do not want to produce a product that may endanger human health. To be sure the costs of assuring a safe and secure food supply are great; however, the cost of failing to do so is far greater. For example, E. coli O157:H7 has cost the beef industry an estimated $2.7 billion in the past 10 years. These costs include $1.6 billion in lost demand for beef. Even these costs pale in contrast to the public health cost attributed to this organism of as much as $1 billion every year.
"If they’d just cook it..." The logic of addressing food safety on the farm
For a long time many in livestock agriculture have believed that food safety concerns should be solved in the kitchen. They have argued that proper preparation of food would largely eliminate dangerous exposures to many food-born pathogens. Unfortunately, rather than accept the risk, consumers may choose not to consume products they don’t trust. Further, the “cook it well” approach does not address exposures from contaminated foods or water consumed without cooking. The fact is, the responsibility for food safety belongs to everyone. Many believe that the best approach for food safety is the concept of multiple hurdles. In this approach interventions to reduce the probability of food being contaminated with pathogens are taken wherever in the food system they might be effective, including during live animal production.
Research of animal production food safety at the University of Nebraska
The ecology of E. coli O157:H7 in beef feedyards
Our understanding of the ecology of E. coli O157:H7 in fed cattle populations has increased greatly in the last six years. We have learned that the organism is ubiquitous to feedlot cattle although the nature of its occurrence is quite dynamic. At any point in time the proportion of cattle within a pen shedding E. coli O157:H7 in the feces varies widely. We can explain some of this variation in prevalence by season and local environmental conditions. Overall, we observed a lower prevalence among cattle fed during winter months (6.5%) compared to summer (30%) even though the prevalence varied widely in both seasons (0-56% in winter, 1-80% in summer). A greater proportion of cattle shedding E. coli O157:H7 was observed when the floor of the pen was wet and muddy. The proportion of cattle shedding E. coli O157:H7 within a population varied widely over time (1-80%) and changes in prevalence were explained by changes in both the incidence and the duration of shedding. We cultured ropes placed in pens for cattle to rub and chew to classify pens of cattle as high (ROPE-positive) or low prevalence at less cost and without disturbing individual cattle. In longitudinal studies conducted over 2 years we observed a higher proportion of ROPE-positive pens of cattle during the summer feeding periods than during the winter. ROPE-positive pens clustered at points in time even among feedyards many miles apart. The proportions of ROPE-positive observations over time were similar from pen to pen within a feedyard. Interestingly, the ecology of E. coli O157:H7 differed from that of Salmonella spp. In total these observational studies have helped us to bridge previous gaps in our knowledge, enabled us to better hypothesize methods to control E. coli O157:H7 in live cattle, and also to design efficient clinical trials to test potential interventions.
Methods to control E. coli O157:H7 in feedyard cattle.
A clinical trial was conducted at the University of Nebraska-Lincoln during the summers of 2002 and 2003 to test the effectiveness of feeding a Lactobacillus acidophilus direct-fed microbial (DFM) to prevent feedlot cattle from shedding Escherichia coli O157:H7 in the feces. Steers (n= 448) were assigned randomly to pens (n=48 pens; 8 hd/pen in 40 pens; 16 hd/pen in 8 pens) receiving either DFM or no DFM in the daily ration. The DFM products were mixed with water and applied to the feed in a mixing box of a separate feed truck (to eliminate the chance of cross contamination) at the rate of 1×109 colony forming units (CFU’s)/steer/day. Fecal samples were collected from each animal every three weeks by rectal palpation in 5 sampling blocks. E. coli O157:H7 was isolated from the samples using selective enrichment, immuno-magnetic separation, and PCR confirmation. Data were analyzed using logistic regression accounting for repeated measures, year, pen and block. Odds ratios were converted relative risk and efficacy was 1-relative risk. Prevalence differed between 2002 and 2003 (p=0.0002). In 2002 the average probability for a DFM-treated steer to shed E. coli O157:H7 over the test periods was 13% compared to 21% among untreated cattle. In 2003 the average probability of shedding was 21% among DFM-treated steers compared to 28% for controls. Over the two years DFM treated cattle were 35% less likely to shed E. coli O157:H7 than cattle in untreated pens (p=0.002). Feeding the DFM product did not affect (P>0.10) overall ADG, DMI, or ADG: DMI. We concluded that feeding this DFM effectively reduced the proportion of feedlot cattle shedding E. coli O157:H7 in feces.
In 2003 a clinical trial was conducted at the University of Nebraska to test the effectiveness of vaccinating feedlot cattle against type III secretory proteins of enterohemorrhagic Escherichia coli on the proportion of feedlot steers shedding E. coli O157:H7 in feces under conditions of natural exposure. Medium-weight steers (N=480) were assigned randomly to 60 pens (8 hd/pen) and to one of four vaccination treatments (2 hd/trt) within pen. Treatments included: 1) no vaccination; 2) vaccinated once at re-implant (d-42); 3) vaccinated upon arrival (d-0) and again at re-implant (d-42); and 4) vaccinated on arrival (d-0), at d-21, and again at re-implant (d-42). An additional 128 steers were assigned to 12 pens within the same feedyard to serve as unvaccinated external controls. Each steer was sampled every three weeks of the feeding period for 1 pre-treatment period (d-0), 2 interim periods (d-21, d-42), and 4 test-period samplings (d-63, d-84, d-105, d-126). From May 8 to September 26 2003, 4260 fecal samples were collected for culture from 608 calves. The data were analyzed by logistic regression accounting for repeated measures, and pen. During the post-treatment period the probability of vaccinated cattle shedding O157:H7 was 11% compared to 29% of unvaccinated cattle. Over the post-treatment period cattle receiving vaccine were 59% less likely to shed O157:H7 compared to external control cattle (p=0.0008). Vaccine efficacy of receiving 1, 2, or 3 doses of vaccine was 52, 58, and 68% respectively, compared with cattle in pens not receiving vaccine. Unvaccinated cattle in treated pens were 50% less likely to shed O157 than cattle in pens not receiving vaccine. We concluded that vaccination effectively reduced the proportion of feedlot cattle shedding O157:H7 in feces, the effect was dose-responsive, and vaccination within a pen also protected unvaccinated pen-mates (herd-immunity). This was the second clinical trial of a vaccine against the type III secretory proteins conducted at UNL. The results of the trial reported here were consistent with the previous study.
Conclusions
The concepts of pathogen control are not new; however, the methods and reasons to apply these concepts are changing. Food quality, safety, and security issues have never been more important to animal production agriculture than now. It is a certainty that these issues will become even more important in the future.
Resources
- A .Potter, S Klashinsky, Y Li, E Frey, H Townsend, D Rogan, G Erickson, S Hinkley, T Klopfenstein, RA Moxley, DR Smith, BB Finlay. 2004. Decreased Shedding of Escherichia coli O157:H7 by Cattle Following Vaccination with Type III Secreted Proteins. Vaccine. (In press)
- D.R. Smith, J.T. Gray, R.A. Moxley, S.M. Younts, M.P. Blackford, S. Hinkley, L.L. Hungerford, C.T. Milton, T.J. Klopfenstein. 2004. A diagnostic strategy to determine the Shigatoxin producing Escherichia coli O157 status of pens of feedlot cattle. Epidem Infect (in press)
- Sargeant J.M., Smith D.R. 2003. The Epidemiology of Escherichia coli O157:H7. In: Microbial Food Safety in Animal Agriculture: Current Topics. Eds. Torrence M. Isaacson R. Iowa State Univ. Press.
- Khaitsa, M.L, Smith D.R., Stoner J.A., Parkhurst A.M., Hinkley S., Klopfenstein T.J.,. Moxley R.A 2003. Incidence, duration, and prevalence of Escherichia coli O157:H7 fecal shedding by feedlot cattle during the finishing period. J Food Prot 66 (11) 1972-1977.
- Kay S. 2003. The cost of E. coli O157:H7. Meat and Poultry. Feb 2003. pp26-34.
- Smith D.R. 2002. Epidemiologic tools for biosecurity and biocontainment. Vet Clin N Am Food Animal Pract. 18 (1) 157-175.
- Smith D.R., Klopfenstein T., Moxley R., Milton C.T., Hungerford L., Gray J.T., 2002. An evaluation of three methods to clean feedlot water tanks. Bovine Practitioner. 36 (1) 1-4.
- Irwin K.E., Smith D.R., Gray J.T., Klopfenstein T.J. 2002. Behavior of cattle towards devices to detect food safety pathogens. Bovine Practitioner. 36 (1) 5-9.
- Smith D.R., Blackford M.P., Younts S.M., Moxley R.A., Gray J.T., Hungerford L.L., Milton C.T., Klopfenstein T.J. 2001. Ecological relationships between the prevalence of cattle shedding Escherichia coli O157:H7 and characteristics of the cattle or conditions of the feedlot pen. J Food Prot 64 (12) 1899-1903.
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