ISRAEL JOURNAL OF
VETERINARY MEDICINE
Vol. 56 (1)) 2000
Review article: HANDLING AND TRANSPORTATION OF BROILERS
WELFARE, STRESS, FEAR AND MEAT QUALITY
Part V: Transport to the slaughterhouse
K. Elrom
The Technion — Israel Institute of Technology, Faculty of Food Eng. &
Biotechnology, 32000 Haifa, Israel. katriel@barak-online.net
Introduction
The transport of live broilers is a multifactorial process which embraces a number of potentially
traumatic events. These events may be described as physical and mental stress factors. Vibration,
sudden acceleration and deceleration of the vehicle, exposure to unfamiliar environments, birds and
noises, climatic changes and pre-slaughter handling are all relatively high stressful factors (1).
The intensity of the induced fear due to transportation is positively related to the duration of the
journey (2). Known responses are increased level in corticosteroids increased rates of heart and
respiration, increased tonic immobility reaction and increased ratio of heterophils: lymphocyts.
Figure 1. Physical and mental stressors during the transportation
Physical stressor
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Temperature : heat and cold.
Wind
Air flow and the gas content
Vehicle vibrations.
Physical injury; bruising, fractures
and dislocations of bones
Mental stressor
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Social mixing.
Food and water deprivation.
Fear and pain
(physical stressors are also indirect mental factors, since they lead to a stress reaction).
Physical and mental stressors
Since it is very hard to separate the physical stressor from the mental ones, one must understand that
physical stressor leads to a mental one also, which may sometimes be even more damaging for the bird
(e.g. a noise which frightens the bird and prevents its normal living habits such as eating or drinking).
Most of the stressors which will be mentioned here have a physical origin but may also induce a mental
stress (pain, fear etc).
Thermal stress
During transportation and when held in lairages at the abattoir, birds may become heat stressed,
particularly on hot, humid days. Because there is no forced ventilation of the crates of birds, ventilation
is often inadequate, and measures to reduce the packing density in the transport containers need to be
implemented to prevent losses (3).
Birds, like mammals, are homeothermic, maintaining body temperatures of 41-420C within an ambient
temperature defined by upper and lower critical limits. The lower critical temp appears to be
approximately 19-220C for males and few degrees above this for females. The upper
critical temperature is around 45-470C, indicating that chickens have quite a wide zone of
thermal comfort (3,4).
If local weather conditions are such that the bird is incapable of maintaining its normal body
temperature, it will be thermally stressed. Heat loss within the zone of thermal comfort occurs mainly
by sensible heat loss, i.e. by conduction, convection, panting and radiation. The rate of heat exchange is
directly related to the temperature differences across a material and thus heat loss or gain may be
modified by introducing insulating layers to reduce the thermal gradient. Plumage provides good
insulation but broilers sometimes have poor feathering. Birds may regulate heat exchange by
vasoconstriction or vasodilatation and behavioral responses such as wing stretching to increase heat
loss or huddling to reduce it (5).
During transportation, flexible behavioral responses are impossible and exposure to certain weather
conditions may result in birds suffering or dying from heat or cold stress. Heat stress appears to be
more common when birds are transported during the daylight (solar radiation), within mutual heating
and decreased heat loss capability. As birds become heat stressed they rely increasingly on evaporative
heat loss (4). Panting adversely alters the microclimate in the crate, making it increasingly difficult for
adjacent birds to lose heat. It is therefore essential that adequate air flow is maintained to replenish the
air around all birds with cooler, drier air. The rate of heat loss by convection and radiation depends on
cooler and drier air. The aerodynamics of poultry transporters is being investigated to optimize poultry
transport thermal environment (6). A model of such a transporter was developed at the Roslin Institute
in the U.K and it seems to fit the requirements.
Heat loss is performed by blood convection to the comb, wattles and feet. Since broilers are
slaughtered when at very young age, blood cooling of the comb and wattles does not give a satisfactory
solution since they are not developed enough anatomically.
During cold stress, which is not very common, hypothermia is likely to occur during cold ambient
temperatures when wind speeds are high. The insulating properties of feathers are significantly
diminished when wet. Moreover birds may also lose more heat by convection because increased
relative humidity increases the conductive properties of air. The use of tarpaulin sheeting on cold days
may worsen the problem in some cases, since the material may cause a pressure drop and pull water
onto the sides of the lorry, soaking the outermost birds. More thought should be given to the design of
this material and to alternative methods. Nicol and Scot (4) quote studies which indicate differences of
200C between inside and outside of the lorry. Intermittent exposure to hot, dry climates has been
shown to increase the heat tolerance of broilers especially females.
During periods of short-term heat stress, changes occur in the cardiovascular and respiratory
systems of the birds, mediated by both chemical and neural mechanisms. Respiration is one of the first
parameters to change during hyperthermia and because the respiratory system is the prime source of
temperature regulation during such conditions, it has been suggested that this physiological mechanism
may be the first to fail when birds succumb to hyperthermia.
Vehicle vibrations
Randal et al.(7) claim that stress is evident in animals during mechanical vibration, which suggests
significant physiological and psychological strain that may lead to symptoms of fear, nausea, distress
or muscular fatigue as observed in humans. The biological response to vibration depends on its
frequency and magnitude. Frequency can be decreased significantly by using air suspension, but it was
not established whether frequency is the main problem. The conscious control may be impaired due to
vibrations that cause the brain to vibrate within the skull and result in concussion injuries.
Behavioral patterns such as orientation, stance, wing extension, flapping and falling indicate severe
welfare standards and may be seen during and mainly immediately after the transportation. Noise is a
stressful stimuli as well as yet not fully investigated (1,8). Vibration is a potential source of stress in
birds because the resonance it sets up in the internal organs are likely to be major aversive stimuli.
Skeletal muscle responds to movement and vibration by maintaining postural stability and reduce the
effects of resonance. Standing birds maintain their stability by wing extension and by flapping or
squatting. Involuntary muscle and cardiac muscle are also affected by vibration with changes in blood
circulation, heart beat and possibly gut control. Broilers of slaughter weight are prone to heart
conditions as an indirect effect of their rapid growth. There is a potential risk of death through heart
failure that would be increased if vibration adversely affected the heart.
A secondary effect of cardiovascular impairment is disturbed thermoregulation. If vasodilatation occurs
due to vibration then temperature control will be affected and the temperature of the organs or of the
body itself will change. Vibrations during transport could effect the body temperature of animals,
particularly if resonance of the internal organs occurs. Animals could be adversely affected when
subjected to resonance during heat stress. Damage ranges from slight rupture of a few cells to sever
impairment of organ function and internal bleeding. Vibration-induced vasodilatation may occur, as
may blood pooling in the organs, pulmonary damage and impaired thermoregulation. Biochemical
changes resulting from vibration could have adverse effects on meat quality in birds unable to recover
before slaughter (8).
Tightening the abdominal muscles prevents abdominal displacement of organs due to resonance. The
contraction of these muscles inhibit the expansion of the air sacs and by doing so, decrease the intake
of oxygen while at the same time the need for O2 is increased due to the need to maintain the tightening
and contraction of the abdominal muscles.
Lairaging (waiting area before slaughter)
To prevent the risk of exposing the birds to additional heat stress while
waiting for slaughter,
slaughterhouses have constructed special areas called lairages where clusters of fans
or ducted ventilation systems are installed with the aim of keeping fresh air moving
over the birds.
The holding area, where broilers are laired, either in situ on the transporter or following unloading, has
to be adequately designed, equipped and operated to safeguard their welfare and prevent any
unnecessary pain or distress. To prevent hyperthermia in warm weather, the holding area must be
ventilated by fixed or mobile fans or by incorporating evaporative cooling systems (9). Very little is
known about the minimum airflow required for various ambient conditions and transportation systems
or if the air really passes through the crates or bypasses them (3).
Shackling
Shackling is stressful not just because it disturbs the normal posture of the animal, which is inverted
during shackling and not only because it is a fearful event but also because it may be very painful.
There are great considerable differences between the thickness of broiler shanks (inter-sex and within
the same sex) so birds with thick shanks require some force while inserting the legs. Compression of
the periosteum in this situation may be very painful for the bird (10).
References
1. Jones, R. B.: Fear and adaptability in poultry: insights, implications and imperatives. World’s
Poult. Sci. J., 52: 131-173, 1996.
2. Cashman, P. J., Nicol, J. C. and Jones, R. B.: Effects of transportation on the tonic immobility
fear reactions of broilers. Br. Poult. Sci, 30: 211-222, 1989.
3. Kettlewell, P. J.: Physiological aspects of broiler transportation. World’s Poult. Sci. J., 46: 219225, 1989.
4. Nicol, C. J. and Scot, G. B.: Pre-slaughter handling and transport of broiler chickens. Appl.
Anim. Behav. Sci. 28: 57-73, 1990.
5. Elrom, K.: Stress in Broilers due to pre-slaughter handling and transportation. Submited as thesis
for D.V.M. degree at the University of Veterinary Medicine in Kosice, The