Salmonella intervention strategies at the farm
Scott M. Russell, Ph.D.
Professor
Poultry Science Department
The University of Georgia
Introduction:
It is often difficult to ascertain how Salmonella issues in poultry begin and
what measures should be implemented to prevent them. Chickens may become
colonized through both vertical (from parent stock) and horizontal (environmental)
means. This purpose of this article is to detail how Salmonella colonize poultry and
to explain effective measures for preventing or controlling colonization.
Breeder chicken origin:
Many scientists have implicated breeder chickens as vehicles for vertical
transmission of Salmonella from the breeder chickens to the fertile egg. In 1991,
Cox et al. evaluated egg fragments, paper pads from chick boxes, and chick fluff from
six commercial broiler breeder hatcheries for the presence and level of salmonellae.
Overall, 42 of 380 samples (11.1%) from those hatcheries were contaminated with
salmonellae. Salmonella were detected in 22 of 145 (15.2%), 5 of 100 (4.6%), and
15 of 125 (12%) samples of egg fragments, chick fluff, and paper pads, respectively.
The percentage of salmonellae-positive samples from each of the six hatcheries
were 1.3, 5.0, 22.5, 11.4, 36.0, and 4.3% respectively (Cox et al., 1991). Of the 140
samples randomly selected for enumeration, salmonellae were found in 11 samples.
Four of these 11 samples had greater than 103 salmonellae per sample, 3 others had
greater than 102 but less than 103, and the remaining 4 had less than 102.
Salmonella serotypes isolated were S. berta, S. california, S. give, S. hadar, S.
mbandaka, S. senftenberg, and S. typhimurium, all of which have previously been
isolated from poultry. The authors found that, the incidence and extent of
salmonellae-positive samples found in the breeder hatcheries were much less than
that previously found in broiler hatcheries, meaning that overall, the industry is
reducing Salmonella in breeder chicken populations. Cox et al. (1991) concluded by
stating that the cycle of salmonellae contamination will not likely be broken until
contamination at these critical points is eliminated.
Cox et al. (2000) reported that numerous publications show that Salmonellacontaminated eggs can be produced by artificially inoculating breeding chickens
(Photo 1)
Photo 1: Cobb broiler breeder chicken
(http://www.wattagnet.com/uploadedImages/WattAgNet/Products/Manufacturer/Poultry/Poultry
_International/0711PIproductsCobb.jpg)
Timoney et al. (1989) reported that oral inoculation of laying hens resulted
in infection of the reproductive tract. Challenging the breeder hen with 106
Salmonella cells caused the ovary and oviduct to become infected. Cox et al. (2000)
observed that the egg production rate for infected chickens was unaffected, and
Salmonella was not detected in all fecal samples; therefore an breeders infected with
salmonellae may not always be easily detectable on the farm. For the contaminated
breeder hens, the yolks of 10% of the eggs laid were contaminated with S.
enteritidis. However, when hens were inoculated with Salmonella at levels of 108
cells, a noticeable drop in egg production and signs of pathogenesis occurred (Cox et
al., 2000).
In 2002, Bailey et al. stated that, although the widespread presence of
Salmonella (Photo 2) in all phases of broiler chicken production and processing is
well documented, little information is available to indicate the identity and
movement of specific serotypes of Salmonella through the different phases of an
integrated operation. In the study by Bailey et al. (2002), samples were collected
from the breeder farm, the hatchery, the previous grow-out flock, the flock during
grow-out, and carcasses after processing. Salmonella were recovered from 6, 98, 24,
60, and 7% of the samples, respectively, in the first trial and from 7, 98, 26, 22, and
36% of the samples, respectively, in the second trial. Seven different Salmonella
serotypes were identified in the first trial, and 12 different serotypes were identified
in the second trial (Bailey et al. 2002). Interestingly, for both trials, there was poor
correlation between the serotypes found in the breeder farms and those found in
the hatchery.
Photo 2. Picture of attached Salmonella with flagella.
(http://upload.wikimedia.org/wikipedia/commons/thumb/b/b4/SalmonellaNIAID.jpg/715pxSalmonellaNIAID.jpg)
Semen implicated
Studies have been conducted to determine how vertical transmission from
the breeder to the baby broiler chick occurs. In 1995 Reiber et al. conducted three
experiments to determine the bacteriological quality of rooster semen. The most
frequently isolated genera of bacteria from rooster semen included Escherichia,
Staphylococcus, Micrococcus, Enterococcus, and Salmonella. Most of the bacteria that
were isolated were endemic to poultry and were commonly found in the
environment of chickens (Reiber et al., 1995). Thus, during mating, female breeders
may become inoculated with Salmonella during semen transmission.
Buhr et al. (2005) reported the recovery of Campylobacter (naturally
colonized) from the ductus deferens of 5 of 101 broiler breeder roosters, and four of
those five positive roosters had previously produced Campylobacter-positive semen
samples. Those results prompted further evaluation to determine if inoculation
route influenced the prevalence or level of Campylobacter contamination of semen,
the digestive tract, or reproductive organs. Individually caged roosters, confirmed to
be feces and semen negative for Campylobacter, were challenged with a marker
strain of Campylobacter jejuni either orally, by placing Campylobacter onto the
everted phallus immediately after semen collection, or by dip coating an ultrasound
probe in Campylobacter and inserting the probe through the vent into the colon. Six
days after inoculation, individual feces and semen samples were again collected and
cultured for Campylobacter. Seven days postinoculation, roosters were killed, the
abdomen aseptically opened to expose the viscera, and one cecum, one testis, and
both ductus deferens were collected. Campylobacter was recovered 6 days after
challenge from feces in 82% of samples (log104.1 colony-forming units [CFU]/g
sample), 85% of semen samples (log102.9 CFU/ml), and on the seventh day after
challenge from 88% of cecal samples (log105.8 CFU/g sample). These results
demonstrate that male breeders exposed to Salmonella and Campylobacter may pass
these bacteria on to the female during mating. This helps to explain how vertical
transmission with these pathogens occurs.
The effect of disinfection and rodents
In a study to determine the effect of disinfection on Salmonella in breeders,
three broiler breeder houses at three different locations were sampled before and
after cleansing and disinfection (Davies and Wray, 1996). None of the farms were
able to achieve total elimination of Salmonella Enteritidis from the poultry house
environment. The authors concluded that, in each of the three breeder houses,
failure to eliminate mice from the house that was infected with S. Enteritidis was
likely to be the most important hazard for transmission to the next flock (Davies and
Wray, 1996).
These studies demonstrate that both vertical and horizontal transmission of
Salmonella from breeders and from the environment may occur. Any potential
intervention at this stage of production must focus on controlling Salmonella in
breeders and in the environment of the breeder chickens.
Interventions for breeders:
Over the years, a number of methods have been used to eliminate Salmonella
from breeder chicken populations. One method employed in Denmark, Sweden,
and the Netherlands is to test breeder flocks and, if found to be positive for
Salmonella, slaughter them.
Slaughtering positive flocks:
Rapid increases in the incidence in human salmonellosis in the second half of
the 1980s in Denmark was attributed to the spread of Salmonella in broiler
chickens. Because of this link to poultry, a targeted national control program was
initiated. Initally, the aim of the program was to reduce Salmonella in broiler flocks
to less than 5% prevalence (Wegener et al., 2003). The program was developed
based on the concept of eliminating Salmonella from the breeders, which will then
theoretically ensure that broilers and processed products would be free from
Salmonella. Wegener et al. (2003) reported that infected flocks of breeder chickens
are destroyed, and infected birds are slaughtered. The intensive testing program
developed gradually over time. Birds from Salmonella positive flocks are
slaughtered on separate slaughter lines or late in the day to avoid crosscontamination of Salmonella negative birds. One incentive the Danes give poultry
growers is that farmers get a better price for birds from Salmonella-free flocks, and
slaughterhouses can use the label “Salmonella-free” for birds that meet criteria
determined by the authorities (Wegener et al., 2003). The effect of this program
may be seen in Figure 1 presented below.
Figure 1. Effect of slaughtering Salmonella positive breeder flocks on Salmonella
positive chickens arising from processing operations.
80
70
60
50
40
30
20
10
0
89 90 91 92 93 94 95 96 97 98 99 00 01
However, it is important to note that due to the sheer size of the poultry
industry in the U.S., this approach would be impossible. For example, we produced
roughly twice as much poultry in Athens, GA last year than they produced in all of
Sweden. When we compare the rate of human salmonellosis between Sweden and
the U.S. we find 42.8 per 100,000 people in Sweden versus the U.S. where it is 14.9
per 100,000 people. The question is, “In a country where extraordinarily expensive
measures are used to eliminate Salmonella from the flocks prior to processing, what
are they getting for their money?”
Medications and competitive exclusion:
Scientists have been working for decades in an attempt to control Salmonella
colonization of chickens using bacterial cultures that will colonize the baby chick
and thus, prevent Salmonella from colonizing the chick. Another approach has been
to use antibiotics to prevent colonization of the chickens with Salmonella. In 1997,
Reynolds et al. medicated breeding flocks of domestic fowl (Gallus gallus) using an
antimicrobial treatment followed by competitive exclusion in 13 trials between
February and September 1993. This approach was being used as an alternative to
the Swedish model such that positive flocks would not have to be slaughtered, but
would be treated instead. In each trial, the flock had been confirmed as naturally
infected with Salmonella enterica serovar Enteritidis and the effect of treatment was
determined on Salmonella isolation from internal tissues. Of the 11 trials where
enrofloxacin was used to medicate the flocks, a long-term reduction of Salmonella
was observed in two and a short-term reduction was measured in birds from
another five trials. Salmonella Enteritidis was isolated from birds after treatment in
four other trials with enrofloxacin and in two trials of medication with amoxycillin.
The authors of this study concluded that enrofloxacin significantly reduced the
prevalence of S. Enteritidis in tissues from birds, and reduced the level and
prevalence of Salmonella in the bird’s environment. No Salmonella was identified in
statutory meconium samples taken from the hatched chicks derived from the flocks
after treatment. The program of antibiotic treatment and competitive exclusion
offers an alternative to slaughter, but the approach must be part of a coordinated
program, which will effect a decrease in the prevalence of S. Enteritidis over time by
contemporary use of disease security measures (Reynolds et al., 1997). This
approach in the U.S. may not be acceptable as many companies are trying to
decrease the use of prophylactic antibiotics in order to preclude development of
antibiotic resistant bacteria.
Vaccination:
A number of poultry companies have investigated the use of vaccines for
eliminating Salmonella in breeder flocks. Inoue et al. (2008) stated that young
poultry are very susceptible to Salmonella Enteritidis (SE) infections because of the
absence of complete intestinal flora colonization and an immature immune system
in baby chicks. The authors conducted a study to evaluate the role of passive
immunity on the resistance of young birds against early infections caused by SE. The
progeny of broiler breeders were vaccinated compared to the progeny of
unvaccinated birds. The efficacy of the vaccine was determined by challenging birds
at Days 1 and 14 with SE. After challenge at 1 day of age, the progeny of vaccinated
birds presented a significantly lower number (log10) of SE in liver (2.21), spleen
(2.31), and cecal contents (2.85) compared with control groups (2.76, 3.02, and
6.03, respectively). This means that vaccination in these breeders reduced SE
colonization by greater than 99%. Inoue et al. (2008) observed that examination of
the internal organs, 3 days after infection, revealed that 28% of the birds (7/25)
from vaccinated breeders were positive, whereas 100% (25/25) of the chicks
derived from unvaccinated birds were positive. Moreover, birds that were
challenged at 14 days of age showed a lower number of positive samples compared
with those challenged at 1 day of age, and the progeny of vaccinated birds presented
statistically lower numbers (2.11 vs. 2.94). In this study, age influenced the
susceptibility of birds to SE infections: in control groups, the number of positive
birds at 14 days of age (9/25) was lower when compared with the group infected at
1 day of age (25/25). The number of positive fecal samples of the progeny of
vaccinated birds was significantly lower (36) than those of the control group (108)
after challenge at 1 day of age. The authors showed that vaccinating breeders helped
to increase the resistance of the progeny against early SE infections. However, the
bacteria were not completely eliminated, suggesting that additional procedures are
needed to effectively control SE infections (Inoue et al., 2008).
Most efforts to control Salmonella in breeder flocks in the U.S. have been
concentrated on vaccination programs. In some cases, they are very effective;
however, in others they do not have any effect. In working with one company that
was vaccinating 100% of their breeders, plants receiving the broilers from these
flocks reported a 100% Salmonella positive rate. These data indicate that the
vaccination program in these operations was having no impact and highlights the
importance of identifying the serotypes of Salmonella that are most frequently
isolated and targeting those serotypes in the vaccine (Russell, unpublished data).
Hatchery origins:
Many opportunities exist for Salmonella to be transferred from contaminated
eggs to uninfected baby chicks during the hatching process. Cox et al. (2000)
published an excellent review on this subject. Salmonella may be found in the nest
boxes where breeders lay eggs, in the cold storage egg room at the breeder farm, on
the truck that transports baby chicks to the growout houses, or in the hatchery
environment. All of these situations may cause horizontal contamination of the eggs
with Salmonella. Once transferred, the Salmonella is carried on the surface of the
shell or just beneath the shell if it is able to penetrate the shell. One mechanism for
natural contamination of the eggs is when moist, freshly laid eggs are cooled from
the body temperature of the hen to the air temperature, the internal contents of the
egg shrink, pulling bacteria into the shell through pores (Cox et al., 2000). The
breeder hen’s nest becomes contaminated Salmonella when she brings soil and feces
into it. Smeltzer et al. (1979) demonstrated that eggs laid in wet, dirty nests or on
the floor are more likely to be contaminated with bacteria. It has been known for
over 100 years that salmonellae are able to penetrate egg shells. Moreover,
numerous studies have shown the ability of Salmonella to penetrate and multiply
within the contents of both chicken and turkey hatching eggs (Cox et al., 2000).
There exists significant variability in terms of how well Salmonella can penetrate
eggs (Stokes et al., 1956; Humphrey et al., 1989, 1991). Shell attributes (Sauter and
Petersen, 1974), pH (Sauter et al., 1977), number of pores on an egg shell (Walden
et al., 1956), temperature (Graves and Maclaury, 1962), humidity (Gregory, 1948),
and vapor pressure (Graves, and Maclaury, 1962) are all factors that may effect
penetration (Cox et al., 2000). In spite of the protective effect of the inner and outer
egg shell membranes (Baker, 1974), several researchers have demonstrated that
Salmonella and other bacteria may penetrate these membranes rapidly. Studies
have have shown that bacteria were able to penetrate 25 to 60% of inner
membranes and 10 to 15% of albumen in eggs that were inoculated (Muira et al.,
1964; Humphrey et al., 1989, 1991). Other scientists observed that penetration of
the cuticle and shell of eggs by salmonellae occurred almost immediately in some
eggs. In fact, in one egg, penetration below both membranes was detected as early
as 6 min following shell exposure (Williams et al., 1968). The authors found that,
once bacteria get past the membranes of hatching eggs, there is no way to prevent
their further invasion of the egg contents or developing embryo.
Hatchery Intervention:
The most common approaches to eliminate Salmonella from hatcheries and
to control cross-contamination from contaminated eggs to uncontaminated eggs
during hatching involve disinfection of the surfaces in the incubator and hatching
cabinets and disinfecting the hatching eggs. The problem with disinfecting hatching
eggs is that it is very difficult to get the sanitizer to coat the egg effectively and it is
not advisable to wet the egg during this process. Thus, Russell (2003) conducted a
study to determine if electrostatic spraying was effective for disinfecting hatching
eggs contaminated with Salmonella.
Fertile hatching eggs were coated with Salmonella and separated into 2
groups. The groups were hatched in two separate hatching cabinets. In one
hatching cabinet, water was electrostatically applied to the eggs during hatching to
serve as a control. In the other cabinet, electrolyzed oxidative (EO) water was
electrostatically applied to the hatching eggs to kill Salmonella. Photos 3 and 4
clearly illustrates how much more effective coating a round object using
electrostatic spraying is when compared to using standard misters. In this photo, 2
black balls were coated with a white powder solution. The one in the foreground
was coated using a traditional sprayer. The one in the background was coated using
an electrostatic sprayer. Note the difference in coverage.
Photo 3. Traditional versus electrostatic application of powder to black balls,
simulating an egg.
Photo 4. Traditional versus electrostatic application of powder to black balls,
simulating an egg (different view).
Photo 5 shows the electrostatic application of sanitizer in a hatching cabinet.
Photo 5. Electrostatic application of sanitizer to a hatching cabinet.
This photo indicates that very little material is sprayed into the cabinet
during the electrostatic spraying. Because of this, the eggs do not become wet and
relative humidity does not increase significantly.
Hatchability results for fertile eggs sprayed using electrostatic spraying in
commercial situations (Table 1) and experimental conditions (Table 2) are
presented below. Results for Salmonella typhimurium prevalence in the lower
intestines of broiler chickens from hatching eggs treated electrostatically with tap
water or EO water during hatch are presented in Table 3. These results are
extremely encouraging in that 65 to 95 % (Replicate 1 and 2, respectively) of the
chickens were colonized when only tap water was used to treat the fertile hatching
eggs, indicating that our method for inducing colonization was appropriate;
however, for electrostatically treated eggs using EO water, Salmonella was only able
to colonize one chicken out of forty tested over two repetitions under actual
growout conditions. This research has tremendous industrial application because
many of the companies that are experiencing failures due to high Salmonella
prevalence at the poultry plant are receiving flocks of birds that are 80 – 100%
positive for Salmonella as they enter the plant. It would seem logical to suppose that
if the number of chickens in field that are colonized with Salmonella could be
reduced to the levels observed in this study, the industry would be able to meet the
Salmonella performance standard required by the USDA-FSIS. This research
describes a method that should have tremendous value to the poultry industry for
reducing Salmonella in flocks arriving to the processing plant, which, according to
our research, will translate directly into lower numbers of processed carcasses that
are positive for Salmonella. Moreover, the electrostatic spraying system is not
expensive to incorporate into a commercial hatchery.
Table 1. Results for hatchability of commercial broiler-breeder chicks from hatching
eggs treated electrostatically with tap water or EO water during hatch under
commercial conditions.
Normal Hatch*
Tap Water
EO Water Treated
Treated
Hatchability
85 %
82 %
79 %
n
15,000
15,000
*Fertile eggs used in this study for the EO water treatment were older and expected
hatchability was lower than the normally expected hatch.
Table 2. Results for hatchability of chicks from hatching eggs treated
electrostatically with tap water or EO water during hatch under research conditions
at the University of Georgia Poultry Research Center.
Normal Hatch
Tap Water
EO Water Treated
Treated
Hatchability
92 %
93 %
93 %
n
160
160
Table 3. Results for Salmonella typhimurium prevalence (%) in the lower intestines,
ceca, or cloacae of broiler chickens from hatching eggs treated electrostatically with
tap water or EO water during hatch.
Treatment
Repetition 1
Repetition 2
Tap Water
65 %
95 %
Control
EO Water
0%
5%
Treated
n
20
20
Growout origins:
Even if “Salmonella-free” birds are delivered to the growout house, it is still
possible for them to become colonized during growout. The USDA-Agricultural
Research Service (ARS) to conducted a large epidemiological study to determine the
relative importance of all known sources of Salmonella from the hatchery through
growout and processing in high- and low- production flocks from four integrated
operations located in four states across four seasons (Bailey et al., 2001-Table 4).
Table 4. Salmonella detection percentage from all sample types, times, and
integrators across all seasons and high and low production houses (32 houses and
8,739 samples).
Sample
Total
50.8
6.6
1.4
1.9
10.5
2.3
Integrator
A
32.5
0.8
0.0
0.5
1.6
1.6
Integrator
B
47.4
10.3
1.3
1.3
15.4
3.9
Integrator
C
26.6
9.2
0.0
2.7
15.0
0.0
Integrator
D
96.0
5.2
3.7
3.1
9.4
3.2
Paper pads
Feces
Water line
Water cup
Litter
Feed
hopper
Feeder
Drag swab
Wall swab
Fan swab
Mouse
samples
Wild-bird
feces
Animal
feces
Insects
Dirt, near
entrance
Standing
water
Boot swab
Fly strip
Cecal
droppings
Total
2.3
14.2
3.4
3.4
6.1
0.0
2.1
3.1
1.6
12.5
3.9
21.1
2.6
1.3
0.0
0.0
16.7
7.8
7.8
3.7
4.8
15.6
0.0
3.1
0.0
6.6
6.1
14.3
4.3
4.8
3.0
3.8
0.0
0.0
2.6
2.8
6.1
6.1
6.3
0.8
13.5
4.2
3.3
1.9
0.0
5.1
4.8
4.2
8.3
4.5
12.0
18.7
4.4
14.3
25.0
1.0
16.7
5.3
9.2
11.8
29.6
5.0
6.5
17.1
1.1
9.8
5.2
10.8
9.7
13.4
Reprinted from Bailey et al. (2001)
These data show that Salmonella may be transferred to birds during growout
from rodents, wild birds, and insect vectors, such as beetles and flies. This table
makes it clear that controlling Salmonella during growout requires a comprehensive
approach. Due to the high level detected in the litter and incoming chick paper pads,
it is also clear that vertical transmission is occurring from breeders to hatchery to
the baby chicks. Therefore, any intervention must be able to comprehensively
prevent Salmonella colonization from environmental sources and prevent vertical
transmission.
Growout interventions:
Competitive exclusion:
Researchers have conducted studies using cecal cultures from healthy,
Salmonella free birds in an attempt to develop colonization of the bird’s intestines
with good bacteria that will preclude later colonization of the bird by Salmonella.
Hofacre (2000) reported that establishment of adult intestinal flora in day-old
turkeys using competitive exclusion has been shown highly effective in reducing
Salmonella colonization. The efficacy of two commercial products, a chicken-origin
lyophilized culture (Aviguard, Bayer Animal Health. Merriam, KS) and a probiotic
culture (Avian Pac Soluble Plus, Loveland Industries, Greeley, CO) containing only
Lactobacillus acidophilus, was compared with that of fresh and 24-hr-old turkey
cecal material using the challenge Mead model. The Aviguard was protective, but
fresh turkey cecal material (undefined cecal culture from healthy turkeys) was
significantly more protective in three of the four trials.
Another approach to competitively excluding Salmonella has been to use
starches such as isomaltooligosaccharide (IMO) to enrich cecal bifidobacterial
populations and thus, reduce colonization levels of Salmonella in the ceca of broiler
chickens. Thitaram et al. (2005) prepared broiler starter diets with final IMO
concentrations of 1% (wt/wt), 2% (wt/wt), and 4% (wt/wt) and a control diet
without IMO supplementation. Chickens were divided into 4 groups and challenged
with 108 cell of Salmonella. The IMO-supplemented diets resulted in significantly
higher cecal bifidobacteria compared with the control diet. Chickens fed diets with
1% IMO had a significant 2-log reduction in the level of inoculated S. Typhimurium
present in the ceca compared with the control group. No differences in feed
consumption, feed conversion, or feed efficiency compared with the control group
were observed; however, the result showed a significant reduction in weight for
birds fed 1% IMO diet compared with those fed the control diet.
Higgins in 2007 evaluated the ability of a commercially available lactic acid
bacteria-based probiotic culture (LAB) to reduce Salmonella Enteritidis or
Salmonella Typhimurium in day-of-hatch broiler chicks. In these experiments, LAB
significantly reduced the incidence of Salmonella Enteritidis (60 to 70% reduction)
or Salmonella Typhimurium (89 to 95% reduction) recovered from the cecal tonsils
of day-old broiler chicks 24 h following treatment as compared with controls. In
these studies, LAB treatment significantly reduced recovery of Salmonella in day-ofhatch broilers.
Vaccination:
Many companies have been investigating the use of vaccination of broiler
chickens at the hatchery or during growout to reduce Salmonella colonization of the
live birds. Babu et al. (2004) showed that cell-mediated immunity (CMI) was
enhanced by live Salmonella vaccine (LV). A study to evaluate the impact of live and
killed Salmonella vaccines on Salmonella enteritidis (SE) clearance. Chickens were
first immunized at 2 weeks of age followed by a booster dose at 4 weeks, challenged
with live SE vaccine 2 weeks later (6-week-old) and tested. The results suggested
that the live Salmonella vaccine protected against SE infection, probably by
enhancing cell mediated immunity (Babu et al., 2004).
Acid in waterers during feed withdrawal:
Salmonella in the crops of chickens that have consumed litter may be spread
from carcass to carcass during the crop removal process (Hargis et al., 1995, and
Barnhart et al., 1999). During cropping, the cropper piston is inserted into the vent
area of the carcass and continues through the entire carcass, spinning as it goes.
The piston has sharp grooves on the end of it that pick up the crop and wraps the
crop around the end of the cropper piston. As the piston moves through the neck
opening, the cropper piston comes in contact with a brush that removes the crop
from the piston. Then, the piston, while spinning, goes back through the entire
carcass. If the crop breaks during this removal process, the contents leak onto the
cropper piston and are transferred to the interior and exterior of the carcass,
possibly spreading Salmonella.
Studies have been conducted by Dr. Allen Byrd of the USDA - Agricultural
Research Service (ARS) in which the crops of live birds were filled with fluorescein
dye. After thirty minutes, the birds were processed. By examining the carcasses at
different stages of processing under a black light, crop contents that were
transferred to the inside or outside of the carcass could be clearly visualized. These
studies have shown that commercial croppers result in a large amount of
contamination of the inside and outside of the carcasses. Thus, efforts should be
made to control Salmonella in the crop prior to the crop removal process.
Some companies have been successful at controlling Salmonella in the crop
by acidifying the bird’s drinking water during the feed withdrawal process. Acetic,
citric or lactic acids and Poultry Water Treatment (PWT) have all been used to
acidify the crop to the extent that Salmonella are unable to survive. Byrd et al.
(2001) found that lactic acid was most effective and that 0.44% lactic acid in the
waterers of broilers during the feed withdrawal period reduced Salmonella
contaminated crops by 80%. This effect carried over to the pre-chill carcasses on
which the prevalence of Salmonella was reduced by 52.4 % (Byrd et al., 2001).
When acidifying drinking water using lactic acid, it is best to gradually expose the
birds to higher and higher levels of acid in the water the week before birds are to be
caught. The key is to make the lactic acid concentration as high as possible while
ensuring that the birds continue drinking the water.
Conclusions:
Preventing colonization of chickens during breeding, hatching, and growout
is challenging. This article details a number of methods that may be used to
decrease or eliminate Salmonella from broiler chickens. However, each company
must balance the cost of implementation of these techniques as there may be more
effective methods that can be used at a lower cost to the company during
processing, to allow the company to maintain Salmonella at low levels.
References:
Babu, U., R. A. Dalloul, M. Okamura, H. S. Lillehoj, H. Xie, R. B. Raybourne, D. Gaines, and R. A. Heckert,
2004. Salmonella enteritidis clearance and immune responses in chickens following Salmonella
vaccination and challenge. Vet. Immunol. Immunopath. 101(3-4):251-257.
Barnhart, E. T., D. J. Caldwell, M. C. Crouch, J. A. Byrd, D. E. Corrier, D.E., and B. M. Hargis, 1999. Effect
of lactose administration in drinking water prior to and during feed withdrawal on Salmonella
Bailey, J. S., N. A. Cox, S. E. Craven, and D. E. Cosby, 2002. Serotype tracking of Salmonella through
integrated broiler chicken operations. J. Food Prot. 65(5):742-745.
Baker, R. C., 1974. Microbiology of eggs. J. Milk Food Technol. 37:265–268.
Bailey, J. S., N. J. Stern, P. Fedorka-Cray, S. E. Craven, N. A. Cox, D. E. Cosby, S. Ladely, and M. T.
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