The focus of the commercial
poultry industry is the production of meat and eggs under
intensive husbandry. The egg component includes production of
white and brown eggs that are either marketed in the hell,
bulk processed, or sold as value-added products.
production consists of approximately 245 million layers, of
which about 98 percent are maintained in cages.
The meat component of the poultry industry consists primarily
of chickens and turkeys, although there is also a relatively
small amount of waterfowl and gamebird production.
production, which has largely moved from range rearing to
total confinement rearing on litter floors, has grown rapidly
from 185 million birds in 1985 to about 300 million today.
Unlike chicken production, where reproduction is by natural
mating, essentially all breeder turkeys are maintained in
sex-separate flocks and reproduction is via artificial
During the past half century, chicken meat production has
changed from being a byproduct of the egg industry to an
industry in its own right, with annual production of more than
7 billion broilers and roasters.
Nearly all broilers and
roasters are reared in confinement on litter floors, while
breeders are confined in 1/3 litter and 2/3 slat houses. The
feed intake of breeders is carefully regulated in order to
maintain targeted weights and prevent obesity.
The poultry industry is the largest (in terms of animal
numbers) and the most highly automated, vertically integrated,
and intensified of the animal production industries.
consequence, there has been a great deal of public concern
about the welfare of poultry. This concern, in turn, has
stimulated a substantial scientific research effort,
particularly in Europe.
Several of the more significant
welfare concerns pertaining to poultry are discussed in the
sections that follow.
It should be kept in mind that many
factors must be considered when evaluating the welfare
implications of a particular management procedure, including
the health, productivity, physiology, and behavior of the
The battery cage system for laying hens was introduced
commercially on a wide scale in the 1950's. Since that time,
it has become the predominant method for maintaining hens.
Cages provide the egg producer with an efficient and
cost-effective means of collecting eggs, disposing of wastes,
reducing feed wastage, maintaining an adequate environmental
temperature, and inspecting the condition of individual birds.
Cages have come under increasing criticism, however, largely
because of the behavioral restrictions that are imposed upon
the birds. Cages do not provide an environment that allows the
expression of behaviors like nesting, perching, and
dustbathing. Space allowances for laying hens have also been
criticized, although how space allowances should be determined
is an extremely controversial topic (1). In their "Recommended
Guidelines of Husbandry Practices for Laying Chickens," the
United Egg Producers suggest 48 square inches per bird as a
minimum space requirement for caged hens; however, the
European Community has mandated a minimum allowance of 75
square inches per bird. (In many European countries, heavier
bodied brown egg layers are preferred to the lighter bodied
white egg layers used in the United States.
Both the European and UEP guidelines can therefore be
interpreted as providing a minimum space allowance of 12
square inches per pound of liveweight, although it is more
common to express space allowances on a per-bird basis.) Some
European countries have either increased this allowance or
outlawed battery cages entirely.
Several alternative production systems are being investigated
in Europe. These vary from more intensive systems like the
get-away cage or the Edinburgh cage (modified battery cages
containing perches, dustbaths, and nestboxes) to more
extensive systems like aviaries, straw yards, and free range
It is still unclear whether the more extensive alternative
systems will prove to be economically viable and also result
in improvements in welfare. In general, both egg prices and
mortality have been found to increase in these systems. In
Britain, for example, free range eggs cost about 50 percent
more to produce than cage eggs (5), largely due to increased
labor costs. Mortality is approximately 4 percent in cages, 9
percent on litter, and 16 percent on range (6).
Most mortality on litter is due to cannibalism, which
represents an important welfare problem for the bird that must
be carefully balanced against the importance of providing
opportunities for the expression of behaviors. In general,
cages still provide the best means for insuring bird health
and egg quality and safety. The cage manufacturer's
recommendations for stocking density should be followed.
Modified cages like the Edinburgh cage (4) are promising
alternatives to conventional cages.
Beak and Toe Trimming
Cannibalism sometimes occurs in poultry, and outbreaks can
result in significant injury and mortality in flocks. A common
procedure to reduce the incidence of cannibalism is beak
trimming, which involves removal of approximately ½ of the
beak. Beak trimming is a part of routine husbandry for laying
hens, but its use in broiler production is much less common.
The beaks of male turkeys may be trimmed to reduce injuries
associated with aggressive behavior.
Although there are numerous publications on beak trimming,
controversy exists concerning if, when, and how trimming
should be performed. Studies have shown that traditional
hot-blade beak trimming after 5 weeks of age can result in
both acute and chronic pain (7,8,9). Precision trimmers that
cut a small hole in the beak causing the tip of the beak to
fall off several days later are now available; this method of
beak trimming has not been thoroughly evaluated from the point
of view of pain. There are currently no husbandry procedures
except reduced light intensities that represent viable
alternatives to beak trimming, although recent evidence
suggests that genetic selection could be used to decrease the
incidence of cannibalism in flocks (9).
Beak trimming should not be used indiscriminately, and a
judgment must be made as to whether the discomfort involved is
necessary in order to prevent or reduce future behaviors that
may be deleterious to the bird. When cannibalism occurs in a
flock, beak trimming becomes therapeutic. When the decision is
made to beak trim, it must be done properly to minimize
long-term effects on behavior and production. Guidelines for
beak trimming different strains of birds are available from
the major breeders.
Toe-trimming is also sometimes used in commercial poultry
production. The middle toe of laying hens may be removed to
reduce eggshell damage, and the toes of breeder chickens and
turkeys may be trimmed to prevent injuries to other birds.
Trimming one toe of breeder chickens does not appear to cause
chronic pain when performed properly (10).
The past decade has seen an increasing trend in the recycling
of layers through induced molting. In birds, plumage is
normally replaced before sexual maturity. This process, called
molting, also occurs after sexual maturity and is associated
with a pause in egg production, which can be lengthy if birds
are permitted to molt naturally. Inducing hens to molt rapidly
extends their productive life and has become a common
procedure in the recycling of layers. There is considerable
literature on induced molting (11). Techniques used to induce
molt include feed restriction; a change in light cycle;
manipulation of dietary ingredients such as calcium, iodine,
sodium, and zinc; and administration of pharmaceutical
compounds that influence the neuroendocrine system, sometimes
coupled with a reduction in photoperiod. These procedures
cause an abrupt cessation of egg production coupled with loss
of body weight and feathers.
Restoration of egg production is accomplished by initially
feeding a diet designed to meet the nutritional requirements
for a non-ovulating, feather-growing hen, followed by feeding
a normal laying hen ration.
The most common procedure used to induce molt is feed
withdrawal. Its popularity as a molting method is probably due
not only to its efficacy, but to the elimination of feed costs
during the withdrawal period. Unfortunately, there is a
paucity of data on the well-being of hens during the
withdrawal and postwithdrawal periods, although feed
deprivation is known to result in both increases in stress
hormones and behavioral changes in poultry (1). Until more
information is available, programs that minimize the length of
the feed withdrawal period (7) should be used whenever
During the past half century, genetic selection, heterosis,
changes in husbandry, improved nutrition, and control of
diseases and parasites have contributed to the escalating
growth rate of meat-type poultry. In the 1940's, broilers
required 12 weeks to reach a market weight of 4.4 pounds;
today they achieve this weight in 6 weeks, and the reduction
by the industry of 1 day per year to achieve this weight
continues unabated. Comparable changes have occurred in turkey
and waterfowl production. The result is greatly improved
efficiency of feed utilization because of reduced maintenance.
Several health and welfare problems seen predominantly in
meat-type birds are related to rapid growth rate. A correlated
response to the selection of turkeys for increased body weight
and a broad breast is the development of deep muscle myopathy
(atrophy of the inferior pectoralis muscle) caused by an
inadequate blood supply to the tissues. Both turkeys and meat
chickens exhibit skeletal disorders, particularly in the bones
of the pelvic limb (femur, patella, tibia, metatarsus) and
their associated tendons. These disorders are not necessarily
associated with body weight or conformation, but instead with
the differential growth of body parts, particularly
accelerated growth of muscle that is not commensurate with
Skeletal abnormalities can be further exacerbated by the
resulting motor impediments. The lack of synchronous growth
among body components in broilers, including the heart and
lungs, can contribute to pulmonary hypertension causing excess
fluids in the body (ascites). An additional problem is "sudden
death syndrome," the cause of which is unknown.
These health problems are of great concern to the poultry
industry, and considerable research is being conducted on the
negative aspects associated with rapid growth in today's
broilers. Relationships are complex, and in some cases neither
genetic nor non-genetic solutions are readily available. Some
alleviation, however, may be feasible by moderating growth
during certain periods in the bird's life.
Broilers and their parent stock have the potential for rapid
early growth and eat at or near the capacity of their
gastrointestinal tract when fed ad libitum. Thus, unless the
feed intake of broiler breeders is limited, the resulting
obesity will have negative effects on reproduction, vigor, and
viability. Under current commercial feed restriction programs,
breeders are fed an amount of feed either daily or on
alternate days that is calculated to achieve and maintain
preferred body weights. Feed restriction of this type has been
shown to be a stressor in broiler breeders, resulting in
increases in activity, aggression, stress hormone levels, and
the performance of stereotyped behaviors (1). Although the
health benefits of commercial feed restriction programs to the
bird outweigh these negative aspects, alternative methods for
controlling body weight in breeders require investigation.
Much concern has been expressed about the negative effects of
crowding in floor-housed and caged flocks with respect to air
quality, disease incidence, and aggression. Crowding in both
broilers and laying hens may lead to higher mortality and
decreased growth and reproduction in individual birds,
although overall economic returns from the flock may be
greater (12, 13). However, there is little evidence to support
the view that crowding increases aggression in broilers.
Broilers are very docile and are also marketed at such an
early age that they have not yet formed a dominance hierarchy
SLAUGHTER, AND CULLING
Birds being sent to slaughter are hand-captured, crated, and
transported by road over varying distances to the processing
plant. Many elements of the transport process can be harmful
to the bird (15,16). These include handling by humans, air
temperature changes, removal of food and water, novelty,
confinement, noise, motion, and mixing with unfamiliar birds.
Improper handling and transport may also result in mortality,
bruising, and bone breakage, with the latter representing a
particular problem with spent laying hens. Mechanical
harvesting may be less stressful to the bird than human
handling (17). However, many problems have been encountered
with regard to the maneuverability of harvesting machines in
commercial houses. Whether harvesting is done by hand or
machine, care should be taken to handle birds gently during
capture and crating and uncrating. Stress should also be
minimized during transportation. USDA has developed guidelines
for air transport of chicks and hatching eggs (18).
Meat birds are slaughtered by being shackled and electrically
stunned in a brine-water-bath stunner, followed by the
severing of the vertebral and/or carotid arteries with an
automatic knife. The stunning currents used are intended to
render the bird insensible temporarily until bleed-out is
completed. Laying hens are usually not stunned, because their
bones, which may be osteoporotic due to lack of exercise and
the high rate of calcium usage for egg formation, break during
the application of an electrical current. Stunning is also not
used for some religious slaughter methods.
Surveys in Europe have shown that approximately 30 percent of
birds processed using a bath stunner are inadequately stunned
before slaughter (19); no comparable surveys have been
conducted in U.S. processing plants. Research is currently
being conducted in England on the welfare aspects of stunning
to induce cardiac arrest and on the use of gas (carbon dioxide
plus argon) stunning (20). Additional research is needed on
the commercial utility of alternative stunning methods. At
present, electrical stunning should be carried out carefully
to ensure maximum efficacy (21).
Because they have little market value, spent hens may now be
slaughtered on-farm. Carbon dioxide delivered via a mobile
killing unit with an on-board delivery system, cervical
dislocation, or instant maceration using a specially designed
high-speed grinder, are acceptable on-farm slaughter methods
when properly performed (22,23). In the past, unhealthy chicks
or surplus male chicks were killed at the hatchery by
suffocation. This practice has essentially been abandoned by
the U.S. poultry industry in favor of more humane methods like
maceration, which result in instantaneous death.
To ensure the health and productivity of their flocks, poultry
producers should continue to employ the "best management"
practices recommended by equipment manufacturers, breeders,
trade organizations, and scientists. Current societal concerns
about the welfare of animals in confinement, however, also
require us to consider the behavioral need of animals. More
research is required to determine if husbandry practices need
to be modified to improve well-being, as well as to assess how
this can be accomplished in a manner that is economically
viable for producers and consumers.