Guidance on Risk
The scientific community continues to work with animal agriculture to
investigate methods to reduce food safety risks through the use of
specific production practices. Although much has been learned about the
ecology of biological, chemical and physical hazards during animal
production, there are as yet no specific production practices addressing
biological hazards that consistently and predictably lead to improvement
in food safety. Results are promising in some cases and those avenues
are still under investigation. A key point to recognize is that risk
reduction interventions that may be expected in the future will
necessarily arise from those areas currently under research, or new
areas added to the research agenda. It is important, therefore, for
producers to be aware of the practices being explored so that they can
have input into the process and raise concerns about (1) areas that are
not currently under investigation that should be, (2) the economic
impact of implementing new practices on the farm, and (3) the impact of
food safety hazards on the marketability of their products.
Management Practices Currently Under Research
Researchers approach the problem of food safety on the farm cognizant
of the need for cost effective and practical methods that reduce
hazards. Appropriate management practices are being explored to find
cost-effective ways to prevent, reduce, or eliminate hazards during
animal production. Of special interest are ways to reduce the risk of
E. coli O157:H7 and Salmonella spp. Currently, no clear
association has been found between management factors and the presence
of E. coli or Salmonella spp. Research, however, shows
promise in certain areas. The following highlights are not specific
practices that can currently be recommended for implementation, but they
show promise and may become recommendations in the future.
|Separating calves from adults shows some
effect in reducing prevalence/shedding of E. coli O157:H7 in
2. Feed and water
|Feed and water may serve as sources by
which E. coli O157:H7 or Salmonella spp. can enter the
production unit. Water trough design is an important factor in the
potential effectiveness of using water chlorination. Cattle should be
prevented from standing in or defecating in the troughs.
Hyperchlorination (2-5 PPM) reduces total Escherichia coli
concentrations 90% over non-chlorinated troughs as long as the
troughs are not contaminated by organic material, such as manure.
Hyperchlorination does not adversely affect the palatability of the
water and had no detectable effect on performance (feed intake, feed
efficiency, or rate of gain). Appropriate chlorine levels are
difficult to maintain and need to be adjusted at least daily.
Providing chlorinated drinking water alone, however, is not enough to
control shedding. There appear to be other unidentified factors at
work that impact the prevalence of animals shedding E. coli
O157:H7, because the percentage of animals shedding tends to peak at
the same time in pens with or without chlorinated drinking water.
Electrolyzed oxidizing (EO) water was shown to kill E.
coli O157:H7 cells in vitro It is produced by exposing deionized
water containing 0.1% (w/v) sodium chloride to an electrolysing
chamber containing an anode and a cathode separated by a diaphragm.
Point source inactivation of potential waterborne pathogens by minimal
concentrations of EO water solutions may be possible. This has not
been tested under field conditions.
3. Antibiotic use
|Although no specific
recommendations can be made for individual antibiotics, preliminary
research studies show that under the limited conditions tested: some
antibiotics (tetracycline, spectinomycin) appeared to have little
effect on shedding, other antibiotics appeared to reduce fecal
shedding of E. coli O157:H7 (ceftiofur, bicozamycin, neomycin),
while some antibiotics appeared to increase shedding (tilmicosin).
Additional research is needed to determine if these observations are
valid. Animals treated with antibiotics that increase shedding of
E. coli O157:H7 should be separated from the herd. Antibiotics
approved for use in cattle are under investigation as a pre-slaughter
treatment to reduce (or eliminate) shedding of E. coli O157:H7
in cattle. Salmonella infections treated with antibiotics have been
shown to prolong pathogen shedding.
treatments other than approved antibiotics
|Pre-slaughter treatments are being
investigated that may dramatically reduce the level of gram negative
bacteria in the rumen and intestinal tract of cattle. They could be
given to cattle/livestock shortly before slaughter and to livestock in
antemortem pens. Examples include:
||In vitro studies and early experimental
trials show that feeding sodium chlorate dramatically reduces the
level of gram negative bacteria, including Salmonella spp. and
E. coli. The Food and Drug Administration is currently
considering whether sodium chlorate is generally recognized as safe
(GRAS), or whether it should be regulated as a food additive, feed
additive, or a drug. Pending FDA determination, sodium chlorate may
not be used in cattle going to slaughter for human food. The tissues
of sodium chlorate treated animals were approved to go into animal
feed during the recent field trial.
||Tasco is an extract from the seaweed
Ascophyllum nodosum, a known source of cytokinins with increased
antioxidant activity, and is currently being fed in commercial
feedlots. Field trials to demonstrate the efficacy of Tasco in reduce
fecal carriage and shedding of E. coli O157:H7 are pending.
- Diet: hay/forage vs. grain
|Using diet as a means to affect pathogen
status continues to be controversial, and there are conflicting
reports in the scientific literature. Feeding hay for a brief period
immediately before slaughter may reduce the risk of food-borne E.
coli infection; however, in one study, the feeding of 100% forage
following a 48 hour fast resulted in a significant increase in the
number of E. coli O157:H7 positive
animals. Forage diets have not eliminated carriage or shedding of
E. coli O157:H7, and forage diets have been associated with
increased duration of shedding of E. coli O157:H7. Feeding of
forage/roughage diets and feeding of specific grains continue to be
investigated as management practices that may increase or decrease
pathogens. There is no scientific support for making a recommendation
on diet at this time.
|Vaccines are being investigated that
produce antibodies that would prevent adherence and colonization of
E. coli O157:H7. This is important because the bacteria must
attach to the intestinal tract in order to cause disease. Vaccines are
being designed to prevent or minimize attachment and colonization by a
variety of mechanisms. Vaccines to intimin (intiminO157),
which is an outer membrane protein adhesin that is necessary for
intestinal colonization, would prevent infection. Intimin is also
necessary for the attaching and effacing lesions observed in E.
coli O157:H7 infections in piglets and neonatal calves.
6. Transgenic feeds
|Research is being planned to construct a
transgenic corn that expresses intiminO157 in its seeds for
testing in weaned calves
|Several competitive exclusion (CE)
products are under development. A pharmaceutical company has purchased
a CE product designed to displace E. coli O157:H7 in the
gastrointestinal tract, and they have received an investigational new
animal drug (INAD) exemption from the Food and Drug Administration to
use the product in cattle intended for use in human food. This CE
product has a seven-day withdrawal time. A field trial has not been
A competitive exclusion product has been developed for swine. It is
not yet commercially available.
||Supplementing cattle with certain
probiotic cultures (two strains of Lactobacillus acidophilus)
has been shown experimentally to decrease the incidence of E. coli
O157:H7 in the feces of finishing beef cattle.
|Bacteriophages are viruses that have a
predator-prey relationship with bacteria. Researchers have had some
success killing Salmonella spp. on poultry carcasses. It
should not be difficult to kill bacteria on beef by applying
bacteriophages internally as well as to carcass surfaces.
Bacteriophages are currently not approved for use on human food.
Progress continues to be made in the search for cost-effective
strategies that can be implemented during animal production to reduce
the risk of food safety hazards entering the farm-to-table continuum.
Research depends upon the production community to provide access to
farms in order to collect the samples needed to determine the ecology of
pathogenic organisms. It is essential to determine the mechanisms used
by pathogens to enter farms, to spread between animals and within the
environment, and the specific conditions that affect pathogen survival.
With this knowledge, interventions can be found to prevent, control, or
eliminate pathogens on the farm.
For further information contact Dr. Alice Thaler, Director Animal and
Egg Production Food Safety Staff at 202-690-2687 or
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