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.
Current 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.
Turkey 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 insemination.
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.
As a 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 animal.
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 (2,3,4).
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 possible.
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 development.
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 (14).
TRANSPORTATION, 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.