46 Chapter 3
have shown that E. coli O157:H7 serotypes
present on animal hides matched those on the
feedlot and transportation trailers (Childs
et al. 2006 ; Woerner et al. 2006 ). Thus,
ensuring hygienic transportation and han-
dling of animals prior to slaughtering, fol-
lowed by hygienic slaughtering practices, are
likely more essential than simply improving
the presentation status of animals (Duffy
et al. 2000 ; Kain et al. 2001 ; Childs et al.
2006 ; Woerner et al. 2006 ). An effective
practice, for example, could be the combina-
tion of animal washing with separation of
washed or clean from unwashed animals and
application of pre - evisceration decontamina-
tion treatment with chemicals. Such practice
has been shown to improve the microbial
quality of cattle carcasses by reducing aerobic
plate count (APC) levels and the prevalence
of E. coli O157:H7 from 56% to 34%
(Bosilevac et al. 2004b ). However, physical
separation of the processing of highly con-
taminated from that of clean animals may be
impractical in some systems of animal pro-
duction, marketing, distribution, and slaugh-
tering (Gill 1998 ).
Other methods for reducing microbial
contamination on external animal surfaces,
include hide - on multiple interventions with
chemicals, such as chlorinated water, or
steam of subatmospheric pressure (at 75 –
80 ° C), on shackled animals before the dehid-
ing process (i.e., after stunning or
exsanguination; McEvoy et al. 2001, 2003 ;
Bosilevac et al. 2004b, 2005 ). Other exam-
ined chemicals include cetylpyridinium chlo-
ride (CPC; 1%), sodium hydroxide (SH;
1.6%), trisodium phosphate (TSP; 4%), or
phosphoric acid (4%; Bosilevac et al. 2004a,
b, 2005 ). Evaluation of such treatments on a
laboratory - scale in model spraying - cabinets
has demonstrated reductions of APC and
total coliform count (TCC) of up to 4 log 10
CFU/cm^2 and of E. coli O157:H7 prevalence
from 44% to 17% on cattle (McEvoy et al.
2001, 2003 ; Bosilevac et al. 2004a, b, 2005 ).
Furthermore, in a comparative evaluation ofpotable water (19 ° C) did not reduce the
number of bacteria, but reduced the incidence
of Salmonella on the neck, belly, and ham
areas of live animals, from 27% (before
washing) to 10% (Bolton et al. 2002 ), and
caused 3 log 10 CFU/cm^2 reductions of artifi -
cially inoculated E. coli O157:H7 (Byrne et
al. 2000 ).
U.S. regulatory guidelines require cattle to
be dry, or at least not dripping, when they are
slaughtered (Reed and Kaplan 1996 ; Sofos
and Smith 1998 ), which can be a constraint
when animal washing is considered before
slaughter. Nevertheless, when animals are
wet or excessively soiled, slaughter speeds
should be reduced to minimize accidental
transfer of contamination from the exterior
of the animals onto the carcass or the plant
environment (Sofos 2002 ). Furthermore,
modifi cations in the steps involved in hide
removal, or in equipment used for hide
removal, may help in minimizing transfer of
contamination onto the carcass surface
(Hadley et al. 1997 ). Considering the above
as well as the reported low magnitude of
microbial reduction achieved by this inter-
vention, animal washing, is mostly accepted
as a means to improve visual appearance, due
to removal of visible contamination of
animals presented in a “ dirty ” state, rather
than to enhance the microbial quality of meat
(Bolton et al. 2002 ). Van Donkersgoed et al.
(1997) found poor correlation between coli-
form and E. coli counts on carcasses with the
presentation status of animals before slaugh-
tering (e.g., score and surface wetness) and
the slaughtering speed, suggesting that there
is signifi cant variability in factors affecting
carcass contamination.
Poor sanitation, hygiene and manufactur-
ing practices pre - harvest, as well as during
slaughtering, fabrication, and processing
may lead to excessively contaminated meat,
even when less heavily soiled animals are
processed. Especially, pre - harvest practices
play a key role on the microbial contamina-
tion of the external animal surfaces. Studies