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Identifying Process Variables for a Low Atmospheric Pressure Stunning-Killing System

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Abstract

Current systems for preslaughter gas stunning and killing of broilers use process gases such as CO2, N2, Ar, or a mixture of these gases with air or O2. These systems, known as controlled-atmosphere stunning-killing systems, work by displacing O2, ultimately to induce hypoxia in the bird, leading to unconsciousness and death. In this study, mechanical removal of O2 by rapidly reducing air pressure was investigated as an alternative to controlled-atmosphere stunning-killing systems. Low atmospheric pressure systems could offer advantages in worker safety and operational gas cost because they operate solely with atmospheric air. This study comprised 2 experiments, one to define the initial range of effective pressures, and the second to determine a recommended process pressure. In experiment 1, 48 female broilers, aged 63 d, were subjected to 6 different pressure treatments, ranging from 70.9 to 17.8 kPa. In experiment 2, 56 male broilers, aged 60 d, were subjected to 7 different pressure treatments, ranging from 35.3 to 17.8 kPa. Birds were individually placed in an airtight vessel and exposed to a pressure treatment for 2 min after the final pressure was attained. Results from experiment 1 showed that the effective range of pressure was between 29.5 and 17.8 kPa, with only 25% of the birds exposed to 29.5 kPa surviving and none of the birds exposed to 17.8 kPa surviving. Experiment 2 used a finer resolution of pressure increments, and the estimated pressure level lethal for 99.99% of the birds was determined to be 19.4 kPa.
©2007 Poultry Science Association, Inc.
Identifying Process Variables for a Low
Atmospheric Pressure Stunning-Killing System
J. L. Purswell,
1
* J. P. Thaxton,† and S. L. Branton*
*USDA-ARS Poultry Research Unit, and †Poultry Science Department,
Mississippi State University, Mississippi State 39762
Primary Audience: Poultry Processors, Researchers
SUMMARY
Current systems for preslaughter gas stunning and killing of broilers use process gases such
as CO
2
,N
2
, Ar, or a mixture of these gases with air or O
2
. These systems, known as controlled-
atmosphere stunning-killing systems, work by displacing O
2
, ultimately to induce hypoxia in the
bird, leading to unconsciousness and death. In this study, mechanical removal of O
2
by rapidly
reducing air pressure was investigated as an alternative to controlled-atmosphere stunning-killing
systems. Low atmospheric pressure systems could offer advantages in worker safety and operational
gas cost because they operate solely with atmospheric air. This study comprised 2 experiments,
one to define the initial range of effective pressures, and the second to determine a recommended
process pressure. In experiment 1, 48 female broilers, aged 63 d, were subjected to 6 different
pressure treatments, ranging from 70.9 to 17.8 kPa. In experiment 2, 56 male broilers, aged 60 d,
were subjected to 7 different pressure treatments, ranging from 35.3 to 17.8 kPa. Birds were
individually placed in an airtight vessel and exposed to a pressure treatment for 2 min after the
final pressure was attained. Results from experiment 1 showed that the effective range of pressure
was between 29.5 and 17.8 kPa, with only 25% of the birds exposed to 29.5 kPa surviving and
none of the birds exposed to 17.8 kPa surviving. Experiment 2 used a finer resolution of pressure
increments, and the estimated pressure level lethal for 99.99% of the birds was determined to be
19.4 kPa.
Key words: broiler, gas stunning, slaughter
2007 J. Appl. Poult. Res. 16:509–513
doi:10.3382/japr.2007-00026
DESCRIPTION OF PROBLEM
Previous research focusing on the develop-
ment and optimization of gas stunning-killing
systems for broilers has used process gases such
as CO
2
,N
2
, Ar, or a mixture of these gases with
air or O
2
to incapacitate hens and broilers prior to
shackling and exsanguination [1, 2, 3]. However,
birds can rapidly recover from exposure to these
gas mixtures; therefore, a stun-to-kill process
has been recommended [2, 4, 5]. Unconscious-
1
Corresponding author: jpurswell@msa-msstate.ars.usda.gov
ness was reported in hens when the O
2
concen-
tration was reduced below 5% O
2
by volume
[6], and less than 2% O
2
by volume is recom-
mended for anoxic stun-to-kill processes [7, 8].
However, in gas mixtures containing CO
2
, un-
consciousness may be induced when higher con-
centrations of O
2
are present with an extended
exposure time [9, 10, 11].
One limitation of gas stunning systems is in
achieving uniform concentrations of gases in the
JAPR: Research Report510
atmosphere surrounding the birds as a conse-
quence of inadequate mixing, which may lead
to pockets of air between the birds, reducing the
effectiveness of the process and prolonging the
process time [7]. Mechanically removing air to
reduce the atmospheric pressure, thereby reduc-
ing the partial pressure of oxygen (P
O
2
), may be
an alternative to controlled-atmosphere stun-
ning-killing systems, because pressure is exerted
uniformly in a vessel and does not depend on
the type of process gas used. The use of reduced
atmospheric pressure as a means of slaughter has
been approved for use in farmed game species
(quail, partridge, and pheasant) in Europe [12].
However, little information exists on the re-
sponses of broilers to reduced atmospheric pres-
sure. Thus, the objectives of this study were to
1) determine the operating range of atmospheric
pressures, and 2) to determine the optimum pres-
sure level required to reliably stun and subse-
quently kill broilers by inducing irreversible ces-
sation of respiratory ventilation movements.
MATERIALS AND METHODS
Test System
The test system was composed of an 83.3-
L cylindrical vessel [13] connected directly to
a rotary vane vacuum pump [14] with a flow
rate of 16.9 m
3
/h; the vessel was equipped with
a translucent acrylic lid for observation. A PC-
based data acquisition and control system [15]
was used to monitor tank pressure and control
pump operation, and tank pressure was mea-
sured with a strain gauge-based pressure trans-
ducer [16]. Inlet and exhaust airflow was routed
by 2 manually actuated ball valves. During the
tests, the inlet valve was closed to isolate the
tank from the external atmosphere, and airflow
was directed through the pump via the second
valve. At the conclusion of the test, the tank was
returned to atmospheric pressure through the in-
let valve. The experiments in this study were
approved by the animal care and use committee
at the USDA-ARS Mississippi State location.
Experimental Design
The upper pressure level (70.9 kPa) was se-
lected based on the allowable range for human
habitats in long-term space exploration [17], and
the lowest level (17.8 kPa) was selected based
on O
2
partial pressures shown to induce uncon-
sciousness in hens [6]. Birds in both experiments
were exposed to the respective treatments for 2
min after final pressure had been attained, and
in each of the 2 experiments, 8 replications per
treatment were used.
In experiment 1, 48 Ross ×Ross 708 [18]
female broilers, aged 63 d, were individually
subjected to the following target pressure levels:
70.9, 60.8, 50.7, 40.5, 29.5, and 17.8 kPa. Pres-
sure levels used in experiment 2 were taken from
the lower range of pressures in experiment 1
that resulted in loss of posture (LOP). With
these pressures from experiment 1, 56 Ross ×
Ross 708 male broilers, aged 60 d, were individ-
ually subjected to target pressure levels of 35.3,
32.1, 29.5, 26.6, 23.6, 20.7, and 17.8 kPa.
Loss of posture, resulting from the inability
to maintain a sitting position or neck tension,
has been noted to occur at the onset of uncon-
sciousness [19, 20]. The occurrence of LOP and
cessation of respiratory ventilation movements
were recorded in experiment 1 as primary re-
sponses of interest from which to determine the
range of operating pressures; a bird was consid-
ered dead when respiratory ventilation move-
ments had ceased. Movement of the keel bone
was used as the major indicator of respiratory
ventilation movement. Elapsed times to LOP
and cessation of respiratory ventilation move-
ments were also recorded in experiment 2 and
were determined with a stopwatch.
Statistical Analysis
Loss of posture and survival were coded as
binary data (occurrence =1; no occurrence =0).
Binary data were compared by using logistic
regression [21, 22] with PROC GENMOD [20].
Time data were compared by using ANOVA
with PROC MIXED [23]. Dose-response rela-
tionships can be described by a sigmoid-shaped
curve [24] of the form (equation [1]):
y=a
1+
x
x
0
b
, [1]
where yis the probability of survival, ais the
asymptotic maximum probability, xis the slope
of transition (1/kPa), x
0
is the midpoint of transi-
PURSWELL ET AL.: LOW ATMOSPHERIC PRESSURE STUNNING-KILLING 511
Table 1. Effect of atmospheric pressure set point on
incidence of loss of posture (LOP) and mortality
(experiment 1)
Incidence Incidence of
Pressure of LOP mortality
(kPa) (%) (%)
17.8 100 100
29.5 100 70
40.5 0 0
50.7 0 0
60.8 0 0
70.9 0 0
tion (kPa), and bis the inflection point for the
asymptotic maximum/minimum.
Survival data were fitted to this equation,
and nonlinear regression analysis was used to
determine the dose-response relationship be-
tween atmospheric pressure and bird responses
[25]. Statistical significance was established at
P0.05.
RESULTS AND DISCUSSION
Experiment 1
Data from experiment 1 are shown in Table
1. The higher pressure treatments (70.9, 60.8,
50.7, and 40.5 kPa) elicited no responses of in-
terest from broilers in this experiment and were
subsequently excluded from further experi-
ments. Loss of posture was observed in all birds
exposed to the remaining 2 treatments (29.5 and
17.8 kPa). Of those birds, 75% exposed to 29.5
kPa and 100% exposed to 17.8 kPa did not sur-
vive the treatment. These data showed complete
separation, and no further statistical analysis was
warranted. The pressure treatments used in ex-
periment 2 were subsequently selected to include
this range.
Experiment 2
The goal of experiment 2 was to determine
the optimal operating pressure for a low-pressure
system. As observed in experiment 1, the propor-
tion of birds surviving and exhibiting LOP in-
creased with increasing atmospheric pressure.
Time to LOP ranged from 34.1 to 50.5 s, and
means are presented in Table 2. The times to
LOP for the lowest 4 pressures (26.6 kPa) are
very similar, ranging from 34.1 to 34.9 s. Time
to death increased with increasing atmospheric
Figure 1. Pressure data for the pumping and holding
phases. Evacuation rates were identical for all
treatments, and only the time to pressure differed.
Holding times were likewise identical (120 s) for all
treatments (experiment 2).
pressure and ranged from 79.1 to 142.8 s (Table
2). Time to cessation of respiratory ventilation
movement was not different between pressures
23.6 kPa; however, these 3 set points differed
from the 26.6- and 29.5-kPa set points (P0.01).
Survival data from experiment 2 were fitted
to equation [1], and the resulting coefficients
were recorded: a=93.3672 (P<0.0001), b=
21.1147 (P=0.01), and x
0
=29.8918 kPa (P
<0.0001), with an SE of 4.2. By using this
equation, we could determine the pressure re-
sulting in the desired proportion of mortality;
for 99.99% mortality, a maximum pressure of
19.4 kPa should be used.
Time to LOP in experiment 2 for birds ex-
posed to pressures 26.6 kPa fell within a narrow
range, showing little correlation with atmo-
spheric pressure. This resulted from the nature
of the pump-down cycle of the test system. With
a constant flow rate and vessel volume, evacua-
tion of the system was highly repeatable, and
the vessel reached the same pressure, with little
variation in time. Pressure measurements were
monitored and recorded throughout the pumping
and holding phases (Figure 1). Taking the aver-
age time to LOP for the lowest 4 pressures (34.5
s) and then determining the pressure at that stage
during the pumping phase, an estimate of the
pressure at which LOP occurs could be deter-
mined. For all birds (n =32) in these 4 treat-
ments, the average pressure after 34.5 s of evacu-
ation was 21.1 kPa, with an SE of 0.8.
JAPR: Research Report512
Table 2. Effect of atmospheric pressure set point on incidence of loss of posture (LOP), time to LOP, incidence
of mortality, and time to cessation of respiratory ventilation movement (experiment 2)
1,2
Incidence Time to Incidence of Time to
Pressure of LOP LOP mortality death
(kPa) (%) (s) (%) (s)
17.8 100 34.5 ±0.7
c
100.0 79.1 ±1.6
b
20.7 100 37.9 ±1.0
c
100.0 85.5 ±1.5
b
23.6 100 34.1 ±1.3
c
100.0 83.4 ±3.8
b
26.6 100 34.6 ±1.6
c
100.0 128.4 ±8.3
a
29.5 100 38.1 ±2.3
bc
62.5 142.8 ±8.7
a
32.1 75 50.5 ±5.4
a
12.5
3
35.3 75 46.7 ±4.3
ab
12.5
3
a–c
Means within a column with no common superscript differ (P<0.05).
1
Birds were exposed to low-pressure conditions for 2 min after the final pressure was attained.
2
Table values represent mean ±SEM.
3
Time to death was excluded for these pressure settings because of the low incidence of mortality associated with them.
Raj and Gregory [7] recommended an O
2
concentration of 2% by volume under nominal
atmospheric pressure, equating to approximately
2.0 kPa P
O
2
, to minimize problems that might
arise from uneven gas distribution. Results of
this study showed that for the case of reduced
atmospheric pressure, reducing P
O
2
to approxi-
mately 3.7 kPa at the lowest pressure of 17.8
kPa was sufficient to stun and kill broilers. The
pressure required for 99.99% mortality (19.4
kPa) would result in a P
O
2
of 4.0 kPa, which is
similar to that of other anoxic systems at nominal
atmospheric pressure with good gas distribution.
Mean time to death at pressures 23.6 kPa was
82.7 s and was similar to those reported for the
Ar, CO
2
, and N
2
processes [9, 10, 26, 27].
The American Veterinary Medical Associa-
tion lists decompression as an unacceptable
means of euthanasia for animals, with the pri-
mary concern that pain and distress could occur
from gases trapped within the body [28]. How-
ever, concerns regarding air trapped in the body
cavity are not applicable to birds. The anatomy
of the avian respiratory apparatus differs from
mammals in many respects. Lungs are fixed and
do not expand and contract; the lungs are
CONCLUSIONS AND APPLICATIONS
1. Controlled-atmospheric pressure reduction appears to be an effective method for humanely
stunning and killing chickens.
2. The mean time to LOP was 34.5 s for pressures 26.6 kPa.
3. The mean time to death was 82.7 s for pressures 23.6 kPa and is similar to times reported for
other controlled-atmosphere processes.
attached to air sacs and ramifications of these
air sacs extend into many bones. Air sacs com-
pletely fill all the vacant space in the thoracic
cavity and much of the abdominal cavity as well.
Birds have only a rudimentary diaphragm, which
does not extend across the interface of the tho-
racic and abdominal cavities. Thus, in poultry,
trapped air pockets in the body cavity are impos-
sible because of the organization of the extensive
respiratory apparatus. Fedde [29] provides an
excellent discussion of the avian respiratory
system.
A low-pressure system may provide eco-
nomic and safety advantages over other gas stun-
ning processes. The process uses atmospheric
air, eliminating the need to purchase process
gases or generate them on site. Safety concerns
about worker exposure to process gases are elim-
inated, and any leaks would bring atmospheric
air into the system, rather than discharging it.
Further studies should address the influence of
evacuation rate and exposure time to refine the
process, determine the effects of this process on
physiological responses and on carcass or meat
quality, and evaluate the welfare aspects of using
this process.
PURSWELL ET AL.: LOW ATMOSPHERIC PRESSURE STUNNING-KILLING 513
4. The estimated operating pressure for a low-pressure stunning-killing system was 19.4 kPa.
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... to 17.8 kPa for two minutes has been shown to be lethal to broilers [15]. However, the requirement for day-old chicks and poults may be different. ...
... In the LAPS treatment, the air pressure inside the chamber was decreased gradually, which subsequently reduced the partial pressure of oxygen. Purswell et al. [15] estimated that a negative atmospheric pressure of 19.4 kPa would result in 99.9% broiler mortality. However, it was found in our laboratory that chicks survived the negative air pressures of 17.9 kPa and 19.4 kPa. ...
... In the LAPS treatment, the air pressure inside the chamber was decreased gradually, which subsequently reduced the partial pressure of oxygen. Purswell et al. [15] Figure 3. Once the required gas concentration or negative air pressure was achieved, chicks were exposed further for a period of 5 min. Chicks were observed for any signs of recovery after the end of that 5 min holding time. ...
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Low atmospheric pressure stunning (LAPS) is a novel approach to pre-slaughter stunning of chickens using progressive hypobaric hypoxia by the application of gradual decompression (280s cycle) according to a set of prescribed pressure curves. Low atmospheric pressure stunning produces a non-recovery state. Concerns have been raised relating to the possible pathological and welfare consequences of expansion of air in the body during LAPS. In a randomised trial, we compared the gross pathology of broilers exposed to LAPS with a control group euthanised by intravenous injection of pentobarbital sodium (60 mixed sex broilers per treatment). The birds were exposed to each treatment in triplets and all birds were subject to necropsy examination to detect and score (1 to 5, minimal to severe) haemorrhagic lesions or congestion for all major organs and cavities (e.g. air sacs, joints, ears and heart) as well as external assessment for product quality (e.g. wing tips). Behavioural data (latency to loss of posture and motionless) and chamber cycle data (temperature, humidity, pressure and oxygen availability) confirmed that LAPS had been applied in a manner representative of the commercial process. All of the organs observed were structurally intact for both treatment groups. No lesions were observed in the external ears, oral cavity, tracheal lumen, crop and air sacs of birds from either treatment group. There was no difference between treatments in the wingtips, nasal turbinates, thymus, biceps femoralis and colon. Haemorrhagic lesions were observed in the calvaria, brains, hearts and lungs of both treatment groups, but lesions in these areas were more severe in the LAPS treatment group. It was not possible to distinguish between pathological changes induced by decompression or recompression. In the barbiturate group, more severe haemorrhagic lesions were observed in the superficial pectoral muscles as well as greater congestion of the infraorbital sinuses, liver, spleens, duodenum, kidneys and gonads. These findings provide evidence that LAPS did not result in distension of the intestines and air sacs sufficient to cause changes, which were grossly visible on postmortem examination. There was also no evidence of barotrauma in the ears and sinuses. The pathological changes observed in the barbiturate treatment were as expected based on barbiturate toxicity. Low atmospheric pressure stunning appears to produce pathological changes by a variety of well-established mechanisms, and while these pathological data have limited value as welfare indicators, the results confirm that organ integrity was not compromised by the process.
... Oxygen levels need to be adjusted to atmosphere equivalent to reflect the physiological impact. The oxygen levels measured were similar to those calculated and reflect those used by Purswell et al., 2007 which found that less than 5% oxygen for 2 minutes was effective to irreversibly stunning poultry from 160 to 280s of pump down. Observations presented in Papers 6, 7 and 8 show that the mean time to motionless is around 145 s and maximum times vary up to 191 s. ...
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Council Regulation (EC) No 1099/2009 on the protection of animals at the time of killing lists in Annex I the stunning interventions currently allowed in the EU, together with the related conditions under which those interventions can be implemented. The regulation allows the Commission to amend Annex I, listing additional stunning interventions, provided they ensure a level of animal welfare at least equivalent to that ensured by the one already approved. EFSA was requested to perform such assessment with regard to the implementation of the low atmospheric pressure stunning (LAPS) system on broiler chickens. The ad hoc Working Group (WG) set up by EFSA performed the assessment in three main steps, i.e. checking the data provided against the criteria laid down in the EFSA Guidance (EFSA AHAW Panel, 2013); running an extensive literature search, followed by data extraction and performing a judgemental ranking exercise based on expert opinion. As main outcome, the LAPS intervention was found to be able to provide a level of animal welfare not lower than that provided by at least one of the currently allowed methods. The overall assessment of EFSA is valid ONLY under the technical conditions described in the submission and for broiler chickens, intended for human consumption, weighting less than 4 kg. Deviations from these conditions might have different consequences for animal welfare which were not assessed in this exercise. The LAPS method may, in addition to commercial slaughter, be suitable for depopulation, respecting the technical conditions defined in the present conclusions. The WG considers that a revision of the present version of the EFSA Guidance could be beneficial.
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The culling of injured and non-viable pigs (Sus scrofa) (neonate to breeding stock) is a routine and necessary procedure on most farms. Usually, pigs are culled using one of the following methods: blunt-force trauma (manual and mechanical), captive-bolt stunners, electrical stunning and electrocution or carbon dioxide. Manual blunt-force trauma is one of the most widely used methods due to its low or absent operational and investment costs. However, as a method, it has serious limitations, which include the risk of incomplete concussion, pain, and distress. Manual blunt-force trauma is also aesthetically unpleasant to operators and wider society. To address these issues there has been significant recent research into the development of alternatives to manual blunt-force trauma, these include: captive-bolt stunners, on-farm, gas-based controlled atmosphere systems, low atmospheric pressure systems and electrical stunning. Some of these are currently in commercial use while others are still in the developmental phase. This review brings together the relevant research in this field, evaluating the methods in terms of mechanism of action (mechanical and physiological), effectiveness and animal welfare.
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Full text pdf available from https://silsoelivestock.co.uk/?post_type=hubble_publications ------------------------------------------------------------------------------------------------------------ Low atmospheric pressure stunning (LAPS) is a slaughter technique which may be less stressful for pigs (Sus scrofa domestica) than current commercial stunning and slaughter methods. The main methods used currently for slaughtering pigs are electric and carbon dioxide stunning, both of which are widely recognised as stressful for pigs. There is currently no published research on the use of LAPS for stunning adult pigs, however there is a significant body of relevant experience from investigations into the effects of low pressure and hypoxia on humans, hypoxia for killing pigs and the use of LAPS for killing poultry, rats and piglets. In this paper, the basic physics and biology of LAPS is briefly reviewed and relevant experience from research with humans, poultry, rats and piglets is presented. On the basis of this information, some initial parameters for LAPS trials with pigs are proposed, potential welfare issues identified and an approach to achieving LAPS at a commercially viable speed is outlined. While the effects of LAPS on pigs is, at present, uncertain, the evidence from research with humans and other animals suggests that healthy, fasted pigs undergoing LAPS are unlikely to suffer from air hunger or from pain. Any pigs suffering from upper respiratory tract disease, tooth decay or excess gas in the alimentary canal may, however, experience pain. A total killing cycle is likely to require 9 to 14 min. To implement LAPS in a commercial, high throughput processing plant will require the use of multiple decompression cylinders. The evidence available suggests that LAPS could be commercially viable for pig slaughter and that for most pigs it will be less stressful than current commercial slaughter methods.
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Introduction to the Logistic Regression Model Multiple Logistic Regression Interpretation of the Fitted Logistic Regression Model Model-Building Strategies and Methods for Logistic Regression Assessing the Fit of the Model Application of Logistic Regression with Different Sampling Models Logistic Regression for Matched Case-Control Studies Special Topics References Index.
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An alternative stunning system to the generally applied electrical water bath stunner for broiler chickens is gas stunning. This method of stunning can eliminate the stress associated with uncrating and/or shackling of live birds prior to electrical stunning. Behavioural responses to inhalation of gas were examined during exposure of broilers to different gas mixtures. In total, 137 six-week-old broiler chickens were individually immersed in a gas chamber containing one of the following gas mixtures: (a) 90% Ar/air, (b) 30% CO2/60% Ar/air or (c) 40% CO2/30% O2/30% N2. The birds moved freely or were restrained. Behavioural parameters were recorded on video and analysed for gasping, headshaking, wing flapping and loss of posture. The number of gasps before loss of posture declined progressively on exposure to gas mixtures Ar/air or Ar/CO2/air or CO2/O2/N2, respectively, and remained high after loss of posture in the latter gas mixture. Gasping occurred rarely in broilers during exposure to gas mixture Ar/air. When gas mixture CO2/O2/N2 was used the loss of posture was significantly delayed compared to the gas mixture Ar/air and Ar/CO2/air. The number of headshakes and wing flapping was significantly higher in the restrained groups of birds compared to the free moving group. Wing flapping was low before and after loss of posture in gas mixture CO2/O2/N2. It is concluded that during the immersion in gas mixtures broilers show gasps, head shakes and wing flapping which start before loss of posture, which may cause some distress. However, it can be argued that gas stunning compared to water bath stunning is preferred in practical applications, because the live broilers do not need to be uncrated and/or shackled.
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From the reviews of the First Edition."An interesting, useful, and well-written book on logistic regression models . . . Hosmer and Lemeshow have used very little mathematics, have presented difficult concepts heuristically and through illustrative examples, and have included references."—Choice"Well written, clearly organized, and comprehensive . . . the authors carefully walk the reader through the estimation of interpretation of coefficients from a wide variety of logistic regression models . . . their careful explication of the quantitative re-expression of coefficients from these various models is excellent."—Contemporary Sociology"An extremely well-written book that will certainly prove an invaluable acquisition to the practicing statistician who finds other literature on analysis of discrete data hard to follow or heavily theoretical."—The StatisticianIn this revised and updated edition of their popular book, David Hosmer and Stanley Lemeshow continue to provide an amazingly accessible introduction to the logistic regression model while incorporating advances of the last decade, including a variety of software packages for the analysis of data sets. Hosmer and Lemeshow extend the discussion from biostatistics and epidemiology to cutting-edge applications in data mining and machine learning, guiding readers step-by-step through the use of modeling techniques for dichotomous data in diverse fields. Ample new topics and expanded discussions of existing material are accompanied by a wealth of real-world examples-with extensive data sets available over the Internet.
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This review summarises information that is relevant to concerns that have recently been expressed about stunning and slaughter. It is known that captive bolt stunning can result in brain material passing to the lungs via the jugular veins. If future studies show that BSE prions pass beyond the lungs to the edible carcass, there will be a move away from captive bolt stunning in large cattle towards electrical stunning. Greater use of electrical stunning in large cattle will increase the importance of blood splash in the beef industry. The theoretical causes of blood splash are reviewed to improve our understanding of this problem. In some situations it can be due to excessive venous pressure causing rupture of a capillary bed some distance from the source of the pressure rise, but it is not known whether this applies to electrical stunning. Gas stunning is replacing electrical stunning for poultry because it can reduce blood spots, which is a similar condition to blood splash. Several gas stunning methods are now being used, but it is not clear which of these is the most humane. Anoxic stunning leads to carcass convulsions and this causes more carcass damage. In fish, recent developments in electrical stunning are showing promise in overcoming problems with carcass damage. It is recommended that rock lobsters should be chilled or frozen before butchery, to ensure a humane death.