Review: Welfare Perspectives on Hens Kept for Egg Production1

REVIEWS Review: Welfare Perspectives on Hens Kept for Egg Production1 J. V. CRAIG and J. C. SWANSON Department of Animal Sciences and Industry, Kansas State University, Manhattan, Kansas 66506

1994 Poultry Science 73:921-938

INTRODUCTION Perceptions of domestic animals' wellbeing have been influenced during the last three decades by criticisms of intensive husbandry systems, beginning primarily with publication of the book Animal Machines (Harrison, 1964). Although some criticisms of high-density systems are justified (as will be apparent in what follows), keeping hens under more natural conditions, in fact, may not be as advantageous in terms of hens' well-being as commonly imagined by critics. For example, observations by the great Norwegian ethologist Schjelderup-Ebbe led him to write the following (Schjelderup-Ebbe, 1922:225; English translation by M. and W. Schleidt): Anyone who thinks the inhabitants of a chicken yard are thoughtless, happy creatures with a daily life of undisturbed pleasure, at peace with each other, and, without a worry about anything, crow, lay eggs, and eat is thoroughly mistaken. A grave seriousness lies over the chicken yard and hens exhibit much anger and fear.

Received for publication October 8, 1993. Accepted for publication March 15, 1994. 'Contribution Number 94-107-J, Kansas Agricultural Experiment Station, Manhattan, KS 66506.

Because cage systems for keeping laying hens have been singled out as particularly undesirable by animal welfare groups, a Scientific Veterinary Committee was appointed by the Commission of the European Community to produce a report evaluating housing systems for laying hens. The committee concluded that "... battery cages have strong advantages above alternative systems, especially in terms of economics, pollution control and working conditions. However, in terms of welfare aspects the alternative systems are preferable" (de Wit, 1992:320). Public criticisms of cage systems have led the governments of Switzerland and Sweden to begin phasing out the housing of laying hens in cages. Recent review articles (Appleby and Hughes, 1991; Mench, 1992; Appleby, 1993) have dealt with methods of evaluating, and presented tentative conclusions regarding the suitability, from a welfare standpoint, of different production systems for laying hens. A book authored by Appleby et al. (1992) has also been published, which gives even broader coverage, including consideration of economic consequences of different systems that have been proposed. Nevertheless, we believed that an additional contribution was justified. We provide a brief account of domestication and how husbandry of egg-strain chickens developed, a somewhat different emphasis on criteria of

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ABSTRACT Welfare issues relative to egg-laying hens are addressed in terms of historical developments and current concerns. Ethical perspectives, attitudes, and public opinion of the past and present are reviewed. Indices of hens' well-being and what those reveal about alternative husbandry practices and production systems are presented along with estimates of economic consequences of alternative systems of table egg production. Possibilities of genetic selection to reduce welfare-related problems are discussed. (Key words: welfare, ethics, hen, management, economics)

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evaluating hens' well-being, a brief discussion of ethical perspectives and current public attitudes about animal use, and an examination of how genetic selection may alter chickens biologically to make them more adaptable to the relatively highdensity systems of production likely to be encountered. HISTORICAL PERSPECTIVE AND CURRENT CONCERNS

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Chickens probably have been domesticated for at least 8,000 yr (West and Zhou, 1989) and they were kept, at least in part, for cockfighting and religious purposes. Hale (1969) indicated that wild ancestors of most species of farm animals shared a number of characteristics that preadapted them to domestication. Included in Hale's list of traits is the absence of highly specialized requirements, which allows them to adapt to a variety of environments. Prior to the 1920s, natural incubation was used, and small flocks of a variety of breeds were kept as part of most mixed farming operations. As knowledge of artificial incubation, nutritional requirements, and disease control developed, flocks were increased in size and kept in houses with roosts, nests, litter to scratch in, and access to outdoor areas except during inclement weather. Soon after World War II, the number of breeds kept for commercial production decreased drastically, and breeders produced dramatic improvements in productivity traits. Labor and housing costs per hen were reduced by technological advances, which included a transition to higher and higher density environments, culminating in multiple-hen cages. Behavioral problems in laying hens changed as flock size and density changed. Broodiness of hens (no longer required) was reduced by genetic selection. Agonistic behavior, including that associated with competition for feed, was observed to be low in small-group-size, high-density cages (Al-Rawi and Craig, 1975; Al-Rawi et al, 1976). Flightiness, including the extreme form of hysteria, became a severe problem in cages containing larger group sizes in some genetic

stocks (Elmslie et al, 1966; Hansen, 1976), and producers responded by reducing the number of hens per cage. Cannibalism and feather pecking, in the absence of beak trimming, were found to be major problems in many stocks in floor-pen flocks (Dun, 1992) and in well-lit cage houses (Craig and Lee, 1990). However, with low levels of lighting those problems are reduced (Gentle, 1986). Another behavior, which appears to indicate frustration of hens of some stocks without access to nests or nest-building materials, is stereotyped pacing prior to oviposition (Mills et al, 1985). Although cages seem to have many advantages, concern is expressed, especially in Western Europe, that welfare is compromised for hens in cages (de Wit, 1992). That view was influenced by the Bramble committee report that stated "An animal should at least have sufficient freedom of movement to be able without difficulty, to turn round, groom itself, get up, lie down and stretch its limbs" (Bramble, 1965:13). The Bramble committee also postulated that animals suffer if they cannot perform behavior patterns seen in their wild relatives. Also, the presence of "vacuum activities" and stereotypic activities are frequently cited as indicators of reduced welfare. In addition, the possibility of fractures causes concern, because hens in cages are known to have increased bone fragility as compared with those in floor pens (Rowland and Harms, 1972; Meyer and Sunde, 1974). The United Kingdom Farm Animal Welfare Council (Webster and Nicol, 1988) stated that husbandry systems should provide freedom from: 1) hunger and thirst; 2) thermal and physical discomfort; 3) pain, injury, and disease; 4) fear and distress; and 5) insufficient space or facilities in which to exercise most normal patterns of behavior. The last "freedom", a modified version of the Brambell Committee's five freedoms (1965), and beak trimming to reduce feather pecking and cannibalism are the most controversial at the present. Although most of the "freedoms" advocated above seem, at first consideration, to be desirable, they are not likely to be entirely achievable. Also, the question

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The debate concerning human treatment of nonhuman animals has historical roots that trace back as far as Aristotle. An abbreviated overview of the topic can assist in establishing the historical nature of the argument (for a more comprehensive review see Rollin, 1981; Regan and

In addition to religious doctrine, philosophers have debated a variety of moral and ethical positions on animal treatment. Rene Descartes (1596 to 1650) concluded that an animal's lack of language was an indication of its inability to conduct rational thought and to possess a

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ETHICAL PERSPECTIVES

Singer, 1989). In brief, Aristotle (384 to 322 B.C.) observed what he referred to as a "natural order" in which " . . . plants exist for the sake of animals and animals exist for m a n . . . " (from VanDeVeer and Pierce, 1986:10). He constructed a hierarchy in which less rational entities exist to serve those that are more rational. Aristotle's observations of nature provided an early justification for the priority given to human interests. In Western culture, religion, in particular the Judeo-Christian ethic, has played an important role in setting traditional values with regard to animal treatment. The concept of human dominion over all of nature is presented in the book of Genesis (1:28): "Be fruitful and multiply, and replenish the earth, and subdue it; and have dominion over the fish of the sea, and over the fowl of the air, and every other living thing that moveth upon the earth." The Judeo-Christian ethic has based its concepts of animal treatment upon the idea of either the human dominance or stewardship of the plant and animal kingdoms. Although concepts of human domination are prevalent, they do not exclude the consideration of humane treatment of animals. Saint Thomas Aquinas made one of the first contributions toward promoting a humane ethic (Rollin, 1981; VanDeVeer and Pierce, 1986; Linzey, 1989). Aquinas was in general agreement with Aristotle's observations. However, he assigned them to a divine origination and meaning. God instructed, as interpreted by Aquinas, that animals were irrational brutes devoid of goodness and thus merit no moral standing. However, Aquinas contended that acts of cruelty to animals should be forbidden because of the callousness it may breed within people. The observation that cruelty to animals can lead to harm in humans forms the basis of a humane ethic that is dominant in Western thought today (Linzey, 1989).

arises as to whether attempts to provide a stress-free environment are desirable in terms of lifetime welfare of hens. It is likely that stressors will eventually challenge all hens, because of unanticipated or uncontrollable events or the ultimate need to terminate their lives as productivity declines with age. In review articles, Gross (1983) and Creel and Albright (1987) provided evidence indicating that an "optimal" level of stress (at least early in life) may be advantageous, because animals are then able to cope better when environmental stressors occur later in life. Nevertheless, as Creel and Albright emphasized, studies are needed to establish schemes for providing optimal levels because there is always the potential for deleterious consequences if stress is too extreme. A study by Deaton et al. (1986) provided an example of how limited daily exposure to the stressor of high temperature, as occurs naturally in the southern region of the U.S. during the summer, protected birds subsequently exposed to a few hours of higher temperature as compared with birds previously kept in a moderate environment. Welfare concerns, such as the presence of social stress in groups of hens under current husbandry systems, have generated considerable discussion about the hens' biological well-being. Such concerns reflect human interests and expectations regarding the use and treatment of animals. The intensity of interest in animal welfare may be attributed to a number of factors, including culture, economics, religious and philosophical beliefs, scientific knowledge, and aesthetics. A basic understanding of how welfare concerns are ultimately generated and manifested in our society is necessary to provide guidance and chart courses for future poultry production practice.

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may allow for the use of animals. However, both philosophers present well formulated arguments against the accepted norm and have spawned controversy over different types of animal use. Attitudes

People express a range of attitudes towards animals. Since leaving the agrarian lifestyle behind, our society has developed varied ethics regarding land and animal use (Sperling, 1988). In the mid-1970s, Kellert (1988) studied public attitudes and knowledge about animals in an effort to assist the U.S. Fish and Wildlife Service plan conservation and use efforts for the future. Kellert found that farmers differed more dramatically in their attitudes towards animals than all other groups measured (professionals, clerical, students, or craftsmen). Farmers were highly utilitarian (interested in animals as resources), whereas most white collar professionals expressed humanistic (interested in animals as companions), moralistic (interested in animals as moral subjects), naturalistic (concerned with wildlife), or ecological (concerned with wildlife and ecosystems) interests. The most prevalent attitudes among all survey participants involved differences towards animal use: 35% had an utilitarian orientation and 37% were moralistic. Levels of concern expressed for animals varied from humanistic, 23%, to neutralistic (having no interest in animals), 25%. Kellert's work demonstrated how society was changing and identified the two areas in which society would tend to have conflict. Kellert also explored age-related differences. As Americans age, their attitudes towards animals change from humanistic, moralistic, and naturalistic towards utilitarian, neutralistic, or dominionistic (interest in dominating animals). An alternative explanation for this phenomenon is that the older population represents closer ties to the agrarian lifestyle than the younger generations. Thus, Kellert's results may show a changing of the guard in prevailing attitudes. In a more recent survey [American Medical Association (AMA), 1989], a similar pattern of differences with aging emerges in regard to concepts relating to animal welfare, rights, and their

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mental life. To Descartes, animals are merely "automata". Immanuel Kant (1724 to 1804) qualified beings capable of autonomy, rationality, and conceptualizing good as entitled to moral standing. Arguments developed by Descartes, Kant, and others tend to support humans as the primary subjects deserving of moral standing, thus relieving us of direct moral duties to animals (Rollin, 1981). Jeremy Bentham (1748 to 1832) was among the philosophers who disagreed with this logic. Bentham (a utilitarian) proposed that the qualifications for moral standing should be attached to a more universal characteristic: the ability to feel (sentience). Bentham argued: "The question is not, Can they reason? nor, Can they talk? but, Can they suffer?" (from VanDeVeer and Pierce, 1986:6). His argument is grounded in the utilitarian maxim to act to create the greatest good (pleasure) for the greatest number and to minimize pain and suffering. Therefore, Bentham asserts that sentience is given priority over rationality or language (Rollin, 1981; VanDeVeer and Pierce, 1986; Regan and Singer, 1989; Callicott, 1992). In 1975, utilitarian philosopher Peter Singer popularized Bentham's argument. By using sentience as a basis for equal moral consideration and pairing it with societal judgments on forms of human discrimination (racism and sexism), Singer provided the needed platform to legitimize the concept of animal rights. However, not all animal rights philosophers agree with Singer's approach. Regan (1983) rejects Singer's use of utilitarian principles and offers a more fundamental approach to animal rights. In concert with other rights-based arguments, Regan believes that animals have inherent value, interests, and needs similar enough to humans that they are deserving of equal moral standing. He contends that viewing animals as a resource is fundamentally wrong and that human conditions should bear no weight when deciding animal treatment. Both Singer and Regan recognize differences between animals and humans and are careful to delineate them in their arguments. Neither suggests that all rights of animals should be exactly the same as humans, and Singer's approach

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identified with only regulatory aspects of controlling animal population) has been merged with welfare to reflect the mutual interests and goals that have evolved to make them nearly identical. Animal use advocates (identified as farmers or researchers) fall on the conservative side of animal welfare, whereas animal rights advocates (identified as wanting to establish moral and legal standing for animals) fall on the radical side. Orlans noted that all three categories are representative of welfare advocacy but involve various degrees of interest and approaches to interpretation and resolution to welfare problems. For example, animal use advocates generally look toward self-regulating programs, guidelines, and entities to educate and "adjudicate" welfare problems, whereas animal protection organizations (organized humane and rights-oriented groups) tend toward law enforcement and legislative efforts to ensure public interests in animal welfare. It is wise to note that attitudes relating to animals fall on a continuum and that attempted categorizing is only to assist in understanding the more distinctive elements that help delineate transitions of attitude. Poultry and animal scientists can be found in a number of these categories. Public Opinion

The power of public or consumer opinion surveys with regard to setting political and business agendas is enormous. Polls can help to identify common areas of agreement, demographic differences, and trends. Surveys regarding animal protection and treatment have been administered by the biomedical and agricultural community in order to measure impacts of the animal protection movement, consumer preferences, and opinion [AMA, 1989; Foundation for Biomedical Research (FBR), 1985; Animal Industry Foundation (AIF), 1989,1990; American Farm Bureau Federation (AFBF), 1990; National Cattleman's Association (NCA), 1989]. Surveys conducted by assorted animal production or industry groups have focused on consumer confidence in farmers and ranchers, identification of activities that increase sensitivity to animal use, food safety, technology, environment, and

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support. Younger Americans showed stronger support, and a significant reduction in that support was reflected in each successive, increasing, age category. Others have chosen to identify differences in approach to animal issues by categorizing the various levels of concerns expressed by advocacy activity and established norms (Morgan, 1986; Jasper and Nelkin, 1992; Orlans, 1993). Morgan (1986) classified animal-related organizations into the following categories: animal exploitation, use, control, welfare, protection, rights, and liberation. Each was representative of the different human-animal relationships, ethics, and levels of concern that have evolved on animal issues. For instance, animal exploiters generally believed that animals are here for human use and abuse, do not have feeling, and do not necessarily receive consideration in matters of pain and suffering. Activities associated with this position include dog and cock fighting, bull fights, live pigeon shoots, etc. m contrast, animal liberation advocates espouse that animals are not the property of humans, have inherent rights and interests, and are not to be looked upon as a resource regardless of human benefits. Liberation organizations are fundamentalist (Jasper and Nelkin, 1992) in their approach to animal issues, often show contempt for human activities and established social norms, use condemnation in their rhetoric, and advocate economic reform (rejection of capitalistic systems). Welfare of animals is not a primary concern because of its implied use of animals. Active and passive forms of protest often are utilized to express disapproval. Advocates of animal use, control, welfare, and rights express increasing levels of human obligation, moral concern, and assignment of protective measures and rights. The distinctive characteristic that separates animal rights from liberation is the more pragmatic approach (Jasper and Nelkin, 1992) used in achieving goals toward abolition of use. Rights activities include a cooperative interest in securing protective measures to enhance welfare or eliminate abuses and may be focused on one particular activity (e.g., antivivisection). Orlans (1993) recently revised Morgan's (1986) categories to reflect current trends. The animal control category (previously

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Surveys also have indicated that Americans believe that animals may have rights (Groller, 1990) that need to be protected or that the public has heightened awareness of the movement (NCA, 1989; AIF, 1990). Although most people believe that it is still acceptable to use animals as food resources (70%, AMA, 1989; 85%, Groller, 1990), they are beginning to disapprove of other uses (fur: 79%, AMA, 1989; 63%, Groller, 1990; cosmetic research or testing: 75%, AMA, 1989; 58%, Groller, 1990). The AMA (1989) and AIF (1990) surveys indicated that the respondents did not believe animals have the same rights as humans or that the promotion of their welfare deserved equal consideration. However, respondents very strongly felt that animals deserved equal consideration in matters of pain and suffering (70%, AIF, 1990). Animal "rights" mean different things to different people. In the above surveys, respondents tended to identify protection from pain, abuse, and cruelty and use practices that are perceived as unnecessary activities (e.g., fur production) as the criteria for rights. The responses did not negate utility of animals for what was deemed as justifiable and essential activities, which reflects a welfare orientation and not a liberationist attitude. The variation with which animal rights are defined and identified can result in animal industries mistakenly targeting all "publics" who espouse a concern for animal rights as fundamentalist in nature. Food safety concerns such as the use of pesticides, antibiotics, and growth hormones were often ranked higher than those directly attached to animal welfare (NCA, 1989; AFBF, 1990; AIF, 1990). Environmental issues also received higher concerns. This priority is not surprising. Factors that can pose immediate danger to personal health and safety can be expected to illicit greater public concern. However, these issues have linkages to the management and treatment of the animal itself. Recent introductions of Quality Assurance Programs (QAP) by commodity groups have begun to tie animal treatment and management practices to food safety, health, and environmental issues (Wilson and Bennett, 1993). Theoretically, producers implementing a QAP should produce a superior product that merits

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regulatory issues. They also attempt to identify which of the many "publics" the industry needs to address through public relations and educational efforts. All of the agricultural surveys reviewed indicated that the public holds farmers in high regard. Farmers and ranchers are respected for the contributions they make to an abundance of affordable food. In most surveys that specifically asked if animals cared for by farmers or ranchers were treated humanely, confidence also ran high (68 to 79%). One survey performed in consecutive years (AIF, 1989, 1990) did indicate a slight drop in confidence (79% in 1989 to 76% in 1990), and when respondents were asked whether they favored regulatory protection for farm animals, nearly 68% said yes. The public seems to be moving towards a protective position regarding farm animals and wants assurances that forms of abuse will be prevented. Semantics also has been shown to play a role in public perception of special agricultural practices, such as tail docking and beak trimming (AIF, 1989, 1990). By neutralizing terminology, for example, changing from debeaking to beak trimming or from tail docking to tail trimming, the public's perception of the practice can be altered. Efforts are on-going within the animal production community to remove callous or harsh terminology and replace it with less emotive or provocative terms. Under the circumstances, this may be a sensible approach; however, it does not change the actual practice itself. The reality is that acute or chronic pain can be associated with certain practices. Neutralized terminology, although helpful, may rely on the relative ignorance of the public concerning the actual practice. Potential backlash exists when neutralized terminology deceptively portrays the actual practice as nothing more than a "hair cut" or "trimming toe nails". Consumers treated to graphic descriptions, pictures, and research that point to the opposite conclusion can further erode confidence in the agricultural community. Neutralized terminology is appropriate when accompanied with honest descriptions and explanations of the actual practice and the reasons it is performed. Attempts to fool the public into believing that certain practices involve no pain or discomfort are dangerous.

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INDICES OF WELL-BEING Behavioral Criteria Most European researchers use behavioral criteria as the primary, or sometimes the only, indicators of hens' welfare (Sorensen, 1981; Wegner, 1985; Appleby and Hughes, 1991). Dawkins (1983:1195) was critical of this approach and wrote: At first sight, the growing awareness that an animal's behaviour may be important evidence to have when assessing its welfare is entirely to be welcomed. . . . But there is, amid the encouraging trend of a greater use of ethological data, also a disturbing one of possible misuse of ethology.

Dawkins (1988) considered the absence of behavior patterns seen in the wild as an

invalid criterion of animal suffering. Instead, Dawkins proposed that by measuring the strength of motivation, the amount an animal is willing to work to obtain conditions under which a behavior can be expressed, will identify the relative importance a behavior may have to the animal's welfare. Some behaviors may have more importance to maintaining animal welfare than others. Ethologists have expressed concern about "vacuum activities", in which inappropriate behavior patterns are seen in relatively barren environments, e.g., as when hens in cages go through the motions of dustbathing. Hughes (1980) contended that this kind of behavior is insufficient evidence, in itself, of suffering caused by frustration, because the performance of the vacuum activity may be an adequate substitute for the real activity. Although performance of a vacuum activity may not necessarily translate into suffering, its manifestation can be aesthetically unpleasing and representative of conditions that do not support the "natural" behavior that is being replaced. Similar to vacuum behavior, another kind of activity commonly interpreted as indicating "mental suffering" is stereotypic behavior. Stereotypies are persistent, highly repetitious behaviors without obvious purpose. Dantzer (1986:1785) examined a variety of physiological and functional aspects of stereotypies and proposed that, "... the occurrence of stereotypies reflects a cut-off of higher nervous function..." and that animals showing such behaviors "would be unable to feel any emotion while they are engaged in their stereotypies." He pointed out that this kind of activity develops in environments that are restricted or unstimulating. Like vacuum activity, stereotypies may not be directly representative of suffering in the context of an animal experiencing actual pain or mental anguish. It may be a coping mechanism (Dantzer, 1993). However, its appearance as a result of, as Dantzer suggests, restrictive or unstimulatrng environments creates questions of whether the stereotypic behavior can be considered acceptable. Duncan and Petherick (1991:5017) postulated that"... animal welfare is dependent solely on the mental, psychological, and

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greater consumer confidence. Under a QAP, some aspects of individual animal welfare are at least considered. However, the primary focus of a QAP may not always lead to resolution of the ultimate problem. For example, high mortality of egg-laying hens creates a problem of carcass disposal. Composting has been developed as a technique to decrease environmental impacts (a high priority consumer concern). The solution (composting) tends to concentrate on the disposal of dead and unusable chickens but may ignore the cause of the problem: high mortality. Depending on the cause, a QAP may address mortality, too. But if high stocking densities or caging were ultimately responsible for the mortality problem and current economics allow for the absorption of lost chickens, then the ultimate problem may never be addressed. For the consumer of poultry products, QAP are an advance in the right direction. But, QAP, consumer surveys, and public relations techniques can only offer limited assistance in addressing specific concerns about the welfare of egg-laying hens. Longterm solutions to welfare problems will require not only an understanding of societal perceptions and expectations with regard to animal treatment, quality control and production, but also the scientific development and measurement of indices of hen well-being.

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Alternative Criteria From the considerations indicated above, the question arises as to whether a single indicator, such as behavior, should be the measure of hen welfare. Nevertheless, the problem of using only behavior as a single measure of welfare does not diminish its importance as a welfare parameter. Gonyou (1994:in press) very appropriately suggests that " . . . too much emphasis has been placed on using behavior as a means of assessing welfare, and too little on the behavioral basis of welfare problems." Hence, the study of animal behavior may be most effective for increasing well-being by answering questions regarding the welfare requirements of farm animals. It has been shown that any single measure is likely to be inadequate when subtle or long-term stressors are involved, and multiple indicators involving health and impairment of the immune system, physiological indicators of stress, and productivity of individual hens, as well as behavioral indicators of internal states such as pain, fear, and frustration are preferable (Hill, 1983; Craig and Adams, 1984; Consortium, 1988; Mench, 1992). EVALUATION OF HUSBANDRY PRACTICES AND HOUSING SYSTEMS Husbandry Practices Recommendations relating to living and feeding space, social environments, sanitation, temperature, and ventilation have been presented elsewhere (Consortium, 1988). Provision of the recommended con-

ditions is likely to promote the welfare of hens and will not be considered here except for further evaluation of space requirements. Of special concern are the so-called "standard agricultural practices" such as beak trimming, which are condoned by the Consortium (1988) but are condemned by the United Kingdom Farm Animal Welfare Council (Webster and Nicol, 1988). The Consortium's approval of beak trimming is based on the argument that, although this procedure causes pain and discomfort, it provides the long-term benefits of diminished likelihood of feather loss and pain and injuries associated with beakrelated behavior. Although pain and discomfort associated with beak trimming were initially believed to be short-term, there is now both physiological (Breward and Gentle, 1985) and behavioral evidence (Duncan et al, 1989; Craig and Lee, 1990; Gentle et al, 1990; Lee and Craig, 1990,1991) that pain and heightened beak sensitivity persist for several weeks or even months following trimming. Nevertheless, Eskland (1981) and Struwe et al. (1992) found evidence, including plasma corticosteroid concentrations and adrenal weights, that beak-trimmed hens were stressed less than those with intact beaks. Forced molting is a widespread husbandry practice in some major egg production areas in the U.S. The most widely used programs involve subjecting hens to complete feed deprivation, often accompanied by reduced lighting, for periods of 4 to 14 or more d (North and Bell, 1990). Weight loss usually ranges from 25 to 35%, and mortality can amount to about 1.25% for the longer periods. However, weight is usually regained, and subsequent mortality is likely to be somewhat reduced relative to what it would have been without induced molting. From the viewpoint of well-being, forced molting involves a dilemma. Although the hen is placed in what could be a lifethreatening situation if feed deprivation continued too long, there is a benefit in prolonged life expectancy under commercial egg production. With a single induced molt, most flocks will have their life spans increased by more than 50%, and with a second molt life expectancy is essentially doubled. Whether hens suffer much during the period of complete feed deprivation is

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cognitive needs of the animals concerned." This approach is appealing, but research into its ramifications are only now being examined and the strength of animals' preferences and willingness to "work", as Dawkins (1983) suggests, to obtain assumed amenities need to be tested. An example of what can be done is illustrated in a study by Faure (1986). Using an operant conditioning technique, he found that hens rarely worked to obtain more feeder space than is commonly provided for caged birds in Europe.

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unclear. Beuving and Vonder (1978) failed to find much change in plasma corticosterone response associated with 5 d of feed withdrawal. Hembree et al. (1980) observed that, when comparing deprived and control hens during feed withdrawal, total aggressive acts of hens without feed tended to decrease during afternoon periods, more than doubled during a 2-wk recovery period, and then returned to the same level.

A survey of U.S. egg industry practices for 1991 (Bell, 1993) indicated that slightly more than 70% of chicks were reared from Day 1 in cages. The question arises as to whether chicks reared in cages differ in their ability to cope with high-density, conventional cages as compared with comparable chicks reared in relatively spacious floor pens. The novel cage environment might pose a welfare problem for floorreared chicks when they are transferred to it during late adolescence. Craig et al. (1988) examined the behavioral consequences of such an environmental change by contrasting behavior and feed intake of pullets reared in floor pens and cages. Chicks reared in floor pens appeared to be more fearful initially and to engage in more agonistic activity. However, those differences disappeared within a week or two. Subsequent studies, using several stocks and involving long-term production data and behavioral observations of floor- and cage-reared pullets provided results that were generally consistent with those of the earlier study (Jin and Craig, 1988; NaLampang and Craig, 1990a,b). Na-Lampang and Craig (1990a) reported that pullets from either rearing environment adapted readily to either cages or floor pens.

was associated closely with population pressure; the incidence was 91% in a hysteria-susceptible stock with 40 hens per cage. When group size is increased, it is usually done by placing more birds in the same size cage, thereby confounding the effects of group size and density. Al-Rawi and Craig (1975) and Al-Rawi et al. (1976), taking care to avoid the confounding, found a positive association between group size and frequency of agonistic behavior during the first 2 mo after flocks were assembled. Mortality for a 40-wk test period was more than twice as frequent in groups of 14 as in groups of 4, and egg production also was affected adversely by increased group size (Al-Rawi et al, 1976). The five commercial stocks used by them were not equally affected by group size in terms of henhoused egg production; some stocks withstood increases in group size better than others. Larger group size has been associated also with increased fear-related behavior (Kujiyat et al, 1983; Okpokho et al, 1987; Craig and Milliken, 1989). Density Effects in Cages

Increasing density (decreasing floor space per bird) has a curvilinear effect on frequency of agonistic acts (Al-Rawi and Craig, 1975). At densities encountered in commercial cages in the U.S., one effect of decreasing space per pullet is a reduction in the frequency of agonistic acts. A large number of studies summarized by Adams and Craig (1985) indicated that productivity decreased, on an individual-bird basis, and mortality increased as density increased. The effect was clearly nonlinear, and well-being diminished ever more rapidly as space decreased. Higher concenGroup-Size Effects in Cages trations of plasma corticosteroids (suggestStudies comparing hens of different ing greater stress) were generally asgenetic stocks in large-group-size, barren sociated with higher densities in cages (Lei cages are of special interest (Elmslie et al, et al, 1972; Mashally et al, 1984; Craig et al, 1966; Hansen, 1976). In both studies "hys- 1986). Also, fear-associated avoidance and teria" was evident in at least one. stock and escape behavior generally is greater at absent in at least one. When hysterical episodes recurred frequently, Hansen ob- higher levels of crowding (Okpokho et al, served scratches and torn skin, especially 1987; Craig and Milliken, 1989). on the back, and feed consumption and egg Although overt aggressive acts are less production decreased rapidly. Hysteria frequent in high-density cages, hens of the

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of entrapment and feather loss because of abrasion, particularly at the feeder trough. Tauson (1984a,b, 1985, 1986) tested commercial cages and suggested modifications that generally have resulted in significant improvements in hens' welfare. Included are changes that result in reduced toenail length, reduced feather damage because of abrasion, rrtinimization of the danger of entrapment, and reduced injuries when hens are added or removed from cages. Experimental cages have been designed that allow the expression of more behaviors in less barren environments (Bareham, 1976; Hansen, 1976; Robertson et al, 1989; Appleby and Hughes, 1990; Wegner, 1990). Such cages often provide features such as roosts, nests, sandbaths, and feed and water at more than one level. Those modifications have had diverse effects. For example, they reduced hysteria when group size was large (Hansen, 1976), but some adverse consequences also occurred because excreta fell directly on birds below elevated perches and eggs were laid in sandbaths or on horizontal floors. It is not clear that addiConventional versus tional features provided in complex cages Experimental Cages are regarded as necessities by the hen Conventional (i.e., commercial) mul- (Dawkins, 1990). Whether hens suffer mentiple-hen cages currently in use are typically tally if they cannot perform additional barren enclosures constructed of welded activities also is obscure. Cage modificawire. Some cages have solid partitions tions have begun to be studied in step-wise separating them, and ceilings can vary in fashion, and this approach is more logical size of openings and are usually parallel than the simultaneous modifications with floors or can have a portion that slopes characterized by the development of getdownward towards the rear of the cage. away cages attempted earlier (Duncan, Floors slope to allow eggs to roll into a 1992). Assessment of physical components collecting tray, and feed troughs, usually of experimental cages is illustrated by the mounted on the outside, are reached study of Hughes and Appleby (1989), in through openings that allow sufficient which they showed that adding perches to cages not only allowed perching but also space for the head and neck of hens to increased bone strength. protrude over the troughs. Alternative kinds of watering devices are available and can be placed at various locations either within cages, in side panels so as to be Alternative Housing Systems available to hens in adjacent cages, or A description of alternative housing outside the cage and reached through systems appeared recently (Appleby et al, openings in the walls of the cages. Accord- 1992). Known and assumed advantages and ing to a 1991 survey (Bell, 1993), about 98% disadvantages of the alternative systems of hens producing table eggs in the U.S. were described. As is typical of the Eurowere being kept in such cages. pean approach, considerable emphasis has Commercial cages exist in a variety of been placed on the "five freedoms" as sizes and shapes and with different ar- outlined by the Farm Animal Welfare rangements of feeding and watering sys- Council of the United Kingdom (1986). tems that can cause various levels of danger Appleby et al. (1992:207) stated:

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lowest social status nevertheless suffer adverse effects when crowding and competitive feeding exist above threshold values (Cunningham and van Tienhoven, 1983-84,1984). Cunningham et al (1987), in similar experiments, also carried out assays of stress hormone concentrations but were unable to detect differences associated with status using that criterion. Cunningham and his co-workers worked with linear pecking orders only. However, pecking orders in small groups of hens within cages frequently appear to be nonlinear (Craig and Ramos, 1986; O'Keefe et al. (1988), and the effects of status in such groups need to be examined. Also, commercial stocks are known to differ greatly in frequency of aggressive acts when kept in cages (AlRawi et al, 1976). Therefore, it is desirable to extend the kind of studies carried out by Cunningham and his associates to a number of different stocks and to cages in which nonlinear pecking orders exist.

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No housing or management system is likely to be optimal in all respects, and the concept of "welfare plateaus" (Duncan, 1978) is useful, i.e., that ethically acceptable levels of welfare can exist in a variety of housing systems. Humane considerations and desirable industry-public relations require that welfare-related problems should be alleviated in all systems likely to be used, at least within the constraint of costs that the public is willing to bear. It is our contention that caretakers' welfare should be considered also in evaluation of poultry housing. Thus, a deep-litter system for egg production examined by Appleby et ah (1989:552-553) led them to conclude that it "... met the hens' welfare needs in terms of movement and behavioural expression, but perhaps entirely so only at the lowest stocking density." Nevertheless, they found that under the lowest densities, dust was 15 times higher than in a cage house, and during cold weather, when ventilation was reduced, dust levels in the deep-litter system exceeded recommended maxima for short-term exposure by a factor of three. Donham (1993) and Whyte (1993) reviewed human respiratory disease conditions encountered when workers must contend with high levels of dust and gases (such as ammonia) in closed animal housing, and Donham reported that the incidence was at least twice as high as that in nonconfinement operations. Requirements and recommendations by governmental or welfare-advocacy groups should be evaluated critically, because some may be based on faulty or broad assumptions and little or no scientific or practical evidence. As Hill (1986:13) stated: Public concern for animal welfare has caused a spate of research work on systems other than cages for housing commercial egg

laying stock.... Most of the studies have been little more than feasibility studies... little is known about whether these systems improve the welfare of laying hens.

Much of the research on hens' welfare in cages has been carried out in individualhen cages, even though commercial egg production is based on multiple-bird cages. Thus, concern has been expressed because of the stereotyped pacing and vacuum nestbuilding activity seen prior to oviposition among hens of some stocks in single-bird cages (Mills and Wood-Gush, 1985; Mills et ah, 1985). On the other hand, Ramos and Craig (1988) found that, although the amount of pacing differed in the stock used between hens about to lay and those not laying in single-bird cages, preovulatory pacing was reduced greatly in multiple-hen cages. Presumably, crowding in the multiple-hen cages reduced the opportunity for such activity. Nevertheless, interpretations as to whether the situation in multiple-bird cages was stressful can vary. Possibly, because of the gregarious nature of hens often seen prior to oviposition and the greater "enclosure" of space in crowded cages, hens about to lay may be stressed less there. As in most studies of this kind, the interpretation of results would have been strengthened by additional kinds of evidence, including physiological indicators of stress in the presence and absence of nests. Recent studies of bone fragility and fractures provide evidence on the welfare of hens in cages and alternative systems. Hens' bones are more fragile when kept in cages than in the Elson terrace system or in percheries (Knowles and Broom, 1990). Nevertheless, the incidences of "old" skeletal bone fractures of hens kept in a perchery system were 17 and 27% in flocks evaluated at 60 and 72 wk of age, respectively (Tucker et ah, 1992). Data from 20 farms having caged layers indicated that the percentage of bones broken because of removal from cages was 14% when they were carefully removed individually as compared to 24% when removed by commercial personnel (Gregory and Wilkins, 1989). Birds sampled from different batches immediately before slaughter varied in incidence of broken bones from 10 to 50%. As Gregory and Wilkins (1989:561) stated, "This implies that there must be particular husbandry and

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Many systems . . . including extensive systems, have problems associated with... 'freedom from pain, injury and disease' and 'freedom from fear and distress.' Indeed, these problems may be worse on occasion in extensive systems than in more intensive systems, for example because of aggression and cannibalism associated with large group size, or because of the preventative beak trimming which is itself a major welfare problem. When these problems occur in extensive systems they are often more difficult to control; because such a system by its very nature is not a controlled environment, producers do not have recourse to strategies such as reducing light intensities, or subdividing flocks.

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ECONOMIC CONSIDERATIONS

Relative costs of egg production in different housing systems are difficult to estimate primarily because of lack of data for systems other than cages. Nevertheless, attempts have been made (Elson, 1985; Haartsen and Elson, 1989). Elson, in particular, has stressed the fact that a higher level of workers' dedication and husbandry skills are needed in noncage systems and that greater variations in outcome are likely within such systems because of lesser control of environmental variables. A cage system meeting requirements set forth in a European Community directive, e.g., allowing 450 cm2 per hen was used for comparison. Costs of production can be stated relative to those of a conventional cage system with a value arbitrarily set at 100. Under those conditions, Elson (1985) estimated relative costs at: aviary, 115; deep litter, 118; strawyard, 130; and free range 150 (or 170). Similarly Haartsen and Elson (1989) arrived at estimates of: aviary, 105 and deep litter, 116. In an internal report within the USDA, King et al. (1983) examined the probable consequences that would result if less

intensive egg production systems were mandated. They pointed out the likelihood of major economic confusion, consumer reactions, large expenditures required for new facilities, geographic displacement of egg production farms, and the replacement of many familyoperated units by large business interests. In addition to comparisons between major housing systems, alternatives within cage housing have been estimated in terms of economics. Elson (1985) based comparisons on cage systems with the space allowance of 450 cm2 per bird being given a relative cost of 100. On that basis, he estimated that space allowances of 560 and 750 cm2 had estimated costs of 105 and 115. With 450 cm2 space and perch, 450 cm2 space, perch and nest, and 450 cm2 space in a shallow cage design, relative costs were estimated as 100, 102, and 102, respectively. Get-away cages with two tiers had a relative cost estimate of 110. Adams and Craig (1985) carried out a survey of the literature published between 1971 and 1983 dealing with the effects of crowding on productivity and profitability. They compared studies in which two to six hens were kept per cage with space allowances relative to U.S. concepts of high, medium, and low density, i.e., with means (and ranges) of: 310 (271 to 348), 387 (355 to 426), and 516 (432 to 561) cm2, respectively. Although detailed data on actual space allowances used in commercial operations were not available, it seems that most U.S. producers use the density level categorized as "high", whereas European Community producers are required to allow space roughly equivalent to the "low" density. Adams and Craig (1985: 238) concluded that "... the overall results suggest a strong curvilinear relationship with performance traits decreasing more rapidly at higher densities." Nevertheless, "profitability" had a complex relationship with density; crowding was more profitable when egg prices were high and feed prices low. Under those circumstances, net income was higher when hens were crowded, even though they laid fewer eggs, had higher mortality, and consumed more feed per dozen eggs laid.

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handling procedures which are particularly likely to lead to weak and broken bones." Crowding in floor pens seems to have moderately adverse effects on productivity and well-being (Siegel, 1959). Group size and density effects in that environment need further study, particularly with the advent of alternative housing in which hens live on several tiers within the same pen. Evidence is not consistent in indicating whether chickens in larger flocks in noncage housing systems tend to live in neighborhoods and show home-range or territorial behavior (McBride and Foenander, 1962; Craig and Guhl, 1969; Pamment et al, 1983) or not (Gibson et al, 1988; Appleby et al, 1989). If hens live within neighborhoods in pens, then low social status is likely to have adverse effects (Lee et al, 1982), but the effect on a hen of living in a large flock without social organization is unknown.

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produced significant changes within a few generations (Guhl et al, 1960; Craig et al, 1965; Siegel, 1965; Faure and Folmer, 1975; Mills et al, 1985; Kuo et al, 1991; Craig and Muir, 1993). For example, the incidences of beak-inflicted feather loss and cannibalism in stocks troubled by these behaviors were greatly reduced after two generations of direct selection (Craig and Muir, 1993) and after four generations of indirect selection (Craig and Muir, 1991; Kuo et al, 1991). Traits essential to fitness in the wild may be of little or no importance in modern systems of production. Broodiness is such a behavior. Geneticists raised the GENETIC ADAPTATION threshold for expression of this trait to As indicated earlier, there is concern for such a high level that only rarely is it seen hens' welfare when birds are kept in high- now in highly productive stock. Appardensity environments, because some ently, hens are no longer motivated to genetic stocks exhibit behavior-causing show this previously essential behavior, problems associated with low social sta- and concern about its absence is not tus, flightiness, hysteria, and feather and expressed. With the example of broodiness cannibalistic pecking. Those behaviors are in mind, one may ask, Why should likely to result in reduced productivity, behaviors that are no longer required be feather loss, pain and injuries, and mortal- expressed? Presumably, most or all such ity. Some behaviors are more likely to be behaviors could be eliminated by genetic seen in cages and others in alternative selection between or within stocks, so that hens would not be motivated to show housing systems. A solution to reducing or preventing them or be frustrated by the absence of harmful behaviors would be to use stocks environmental conditions allowing their that either do not show those behaviors or expression. exhibit them at such low levels or so infrequently as to be of trivial importance. SUMMARY Thus, Craig et al. (1983) found that two The wild ancestors of chickens, along White Leghorn stocks derived from the same foundation population exhibited with those of most other farm animals, large differences in avoidance and escape were preadapted to domestication because behavior. Hysteria-susceptible and their lack of specialized requirements hysteria-resistant commercial stocks were allowed them to adapt to a wide variety of found fortuitously by Elmslie et al. (1966) environments provided by humans. Curand Hansen (1976), when hens were rently most commercial chickens kept for placed in large-group-size cages. Within table-egg production are incubated, the White Leghorn breed, stocks have reared, and maintained as productive been identified that differ greatly in adults in high-density, artificial environfeather and cannibalistic pecking. In at ments. Nevertheless, there are limits to least one stock, the incidence of beak- adaptability as indicated by behavioral, inflicted feather loss and injuries was so physiological, immunological, and inlow that beak trimming produced no dividual productivity indicators when enbenefits, although other stocks kept in the vironmental conditions become extreme. same house required beak trimming to However, with the exception of obvious perform well (Craig and Lee, 1989, 1990). injury, no single criterion is likely to be Genetic selection for levels of expres- adequate. Multiple indicators are required sion of behavioral traits generally has to obtain reliable evaluation of whether

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Roush published papers, based upon statistical and mathematical approaches, which provided estimates of optimal density for economic returns and, from biological responses, the break-even point between crowded and uncrowded conditions (Roush, 1986; Roush et al, 1989, respectively). His analyses produced the conclusion that under assumed economic conditions the number of hens per cage that would produce maximum profit would be greater than the number that would be justified on the basis of biological responses.

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REFERENCES Adams, A. W., and J. V. Craig, 1985. Effect of crowding and cage shape on productivity and

profitability of caged layers: a survey. Poultry Sci. 64:238-242. Al-Rawi, B., and J. V. Craig, 1975. Agonistic behavior of caged chickens related to group size and area per bird. Appl. Anim. Ethol. 2:69-80. Al-Rawi, B., J. V. Craig, and A. W. Adams, 1976. Agonistic behavior and egg production of caged layers: genetic strain and group-size effects. Poultry Sci. 55:796-807. American Farm Bureau Federation, 1990. A National Survey of Americans' Attitudes Toward Farmers, Farm Practices and Food Safety. Prepared by Porter/Novelli for American Farm Bureau Federation, Park Ridge, IL. American Medical Association, 1989. Public Attitudes about the Use of Animals in Biomedical Research: Focus Groups and National Surveys of Adults and Children: A Summary of Finding. Compiled from: Public attitudes about the use of animals in biomedical research: A qualitative study, prepared by LaScola Qualitiative Research, April 1989, and "Attitudes toward the use of animals in research: A report of findings from national surveys of adults and children." prepared by Meilman and Lazarus, Inc. August, 1989. The American Medical Association, 535 N. Dearborn, Chicago, IL. Animal Industries Federation, 1989. Survey Results on How Americans View Modern Livestock Farming. Prepared by BMc Strategies for Animal Industries Foundation, Arlington, VA. Animal Industries Federation, 1990. American Attitudes Toward Farmers and Farm Animal Issues. Prepared by Opinion Dynamics for Animal Industries Foundation, Arlington, VA. Appleby, M. D., 1993. Should cages for laying hens be banned or modified? Anim. Welf. 2:67-80. Appleby, M. D., and B. O. Hughes, 1990. Cages modified with perches and nest sites for the improvement of welfare. World's Poult. Sci. J. 46:38-40. Appleby, M. C, and B. O. Hughes, 1991. Welfare of laying hens in cages and alternative systems: Environmental, physical and behavioural aspects. World's Poult. Sci. J. 47:109-128. Appleby, M. C, B. O. Hughes, and H. A. Elson, 1992. Poultry Production Systems: Behaviour, Management and Welfare. C.A.B. International, Wallingford, Oxon, England. Appleby, M. C, B. O. Hughes, and G. S. Hogarth, 1989. Behaviour of laying hens in a deep litter house. Br. Poult. Sci. 30:545-553. Bareham, J. R., 1976. A comparison of the behaviour and production of laying hens in experimental and conventional battery cages. Appl. Anim. Ethol. 2:291-303. Bell, D., 1993. The egg industry of California and the USA in the 1990s: a survey of systems. World's Poult. Sci. J. 49:58-64. Beuving, G., and G.M.A. Vonder, 1978. Effect of stressing factors on corticosterone levels in the plasma of laying hens. Gen. Comp. Endocrinol. 35:153-159. Bramble, F.W.R., 1965. Chapter 4. The welfare of animals. Pages 9-15 in: Report of the Technical

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husbandry practices and environmental conditions reduce hens' welfare significantly. Concern for the well-being of hens has led to the phasing out of cages in two European countries. Although cages are known to be associated with some problems of well-being, it is known also that they have some welfare advantages for hens over alternative systems of production and they have definite economic advantages for producers. Therefore, it is doubtful whether the use of cages should be denied without exploring further the possibilities of cage modification or genetic selection aimed at improving the well-being of hens in such environments. Ethical perspectives relative to animals have been evolving since the time of Aristotle more than 300 yr B.C. Recent developments include divergence of welfare concerns between utilitarian and animal rights based philosophies. The utilitarians generally agree that animals may be used for human benefit if unnecessary pain and suffering are avoided and humane care and management criteria are met. Fundamentally, rights-oriented groups reject such exploitation. The general public exhibits a continuum of attitudes towards animals. However, there are indications that they are moving towards a protectionist attitude toward farm animals. Many requirements for good husbandry are known. However, uncertainty prevails in some areas, particularly with the necessity of routine procedures such as beak trimming and the amount of space needed, optimal group size, and whether nests, roosts, litter, and other quality of environment features are necessities or luxuries in terms of hens' welfare. Floor and feeder space and group size seem to be of paramount importance, and space that is adequate for well-being seems to be greater than that which yields the greatest net income. Genetic solutions to several behavior-related problems that compromise hens' well-being seem to be feasible and worthy of greater emphasis by commercial poultry breeders.

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Cunningham, D. L., and A. van Tienhoven, 1983-84. Relationship between production factors and dominance in White Leghorn hens in a study on social rank and cage design. Appl. Anim. Ethol. 11:33-44. Cunningham, D. L., and A. van Tienhoven, 1984. The effects of management program and social rank on behavior and productivity of White Leghorn layers in cages. Poultry Sci. 63:25-30. Cunningham, D. L., A. van Tienhoven, and F. De Goeijen, 1987. Dominance rank and cage density effects on performance traits, feeding activity and plasma corticosterone levels of laying hens (Gallus domesticus). Appl. Anim. Behav. Sci. 17: 139-153. Dantzer, R., 1993. Research perspectives on farm animal welfare: The concept of stress. J. Agric. Environ. Ethics 6(Suppl. 2):86-92. Dantzer, R., 1986. Behavioral, physiological and functional aspects of stereotyped behavior: a review and reinterpretation. J. Anim. Sci. 62: 1776-1786. Dawkins, M. S., 1983. Battery hens name their price: consumer demand theory and the measurement of ethological 'needs'. Anim. Behav. 31: 1195-1205. Dawkins, M. S., 1988. Behavioural deprivation: A central problem in animal welfare. Appl. Anim. Behav. Sci. 20:200-225. Dawkins, M. S., 1990. From the animal's point of view: motivation, fitness, and animal welfare. Behav. Brain Sci. 13:1-61. Deaton, J. W., F. N. Reece, S. L. Barton, and J. D. May, 1986. High environmental temperature and broiler livability. Poultry Sci. 65:1268-1269. de Wit, W., 1992. The welfare of laying hens kept under various housing systems. Pages 320-323 in: Proceedings XIX World's Poultry Congress. Vol. 2. Amsterdam, The Netherlands. Donham, K. J., 1993. Respiratory disease hazards to workers in livestock and poultry confinement systems. Semin. Respir. Med. 14:49-59. Dun, P., 1992. Cages are at present still the best system for egg producers. Misset-World Poult. 8:28-31. Duncan, I.J.H., 1992. Guest editorial: Designing environments for animals—not for public perceptions. Br. Vet. J. 148:475-477. Duncan, I.J.H., 1978. An overall assessment of poultry welfare. Pages 79-88 in: Proceedings 1st Danish Seminar Poultry Welfare in Egglaying cages. L. Y. Sorensen, ed. National Commission Poultry Eggs, Copenhagen, Denmark. Duncan, I.J.H., and J. C. Petherick, 1991. The implications of cognitive processes for animal welfare. J. Anim. Sci. 69:5017-5022. Duncan, I.J.H., G. S. Slee, E. Seawright, and J. Breward, 1989. Behavioural consequences of partial beak amputation (beak trimming) in poultry. Br. Poult. Sci. 30:479-488. Elmslie, L. J., R. H. Jones, and D. W. Knight, 1966. A general theory describing the effects of varying flock size and stocking density on the performance of caged layers. Pages 490-495 in: Proceedings, 13th World's Poultry Congress, Kiev, Ukraine.

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Committee to enquire into the welfare of animals kept under intensive livestock husbandry systems, F.W.R. Brambell (Chairman). Her Majesty's Stationary Office, London, England. Breward, J., and M. J. Gentle, 1985. Neuroma formation and abnormal afferent nerve discharges after partial beak amputation (beak trimming) in poultry. Experientia 41:1132-1134. Callicott, J. B., 1992. Animal liberation and environmental ethics: back together again. Page 253 in: The Animal Rights/Environmental Ethics Debate. Eugene C. Hargrove, ed. State University of New York Press, Albany, NY. Consortium, 1988. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Association Headquarters, Champaign, IL. Craig, J. V., and A. W. Adams, 1984. Behaviour and well-being of hens (Gallus domesticus) in alternative housing environments. World's Poult. Sci. J. 40:221-240. Craig, J. V., J. A. Craig, and J. Vargas Vargas, 1986. Corticosteroids and other indicators of hens' well-being in four laying-house environments. Poultry Sci. 65:856-863. Craig, J. V., T. P. Craig, and A. D. Dayton, 1983. Fearful behavior by caged hens of two genetic stocks. Appl. Anim. Ethol. 10:263-273. Craig, J. V., and A. M. Guhl, 1969. Territorial behavior and social interactions of pullets kept in large flocks. Poultry Sci. 48:1622-1628. Craig, J. V., and H.-Y. Lee, 1989. Research note: Genetic stocks of White Leghorn type differ in relative productivity when beaks are intact vs trimmed. Poultry Sci. 68:1720-1723. Craig, J. V., and H.-Y. Lee, 1990. Beak trimming and genetic stock effects on behavior and mortality from cannibalism in White Leghorn-type pullets. Appl. Anim. Behav. Sci. 25:107-123. Craig, J. V., and G. A. Milliken, 1989. Further studies of density and group size effects in caged hens of stocks differing in fearful behavior: productivity and behavior. Poultry Sci. 68:9-16. Craig, J. V., and W. M. Muir, 1991. Research note: Genetic adaptation to multiple-bird cage environment is less evident with effective beak trimming. Poultry Sci. 70:2214-2217. Craig, J. V., and W. M. Muir, 1993. Selection for reduction of beak-inflicted injuries among caged hens. Poultry Sci. 72:411-420. Craig, J. V., N. A. Okpokho, and G. A. Milliken, 1988. Floor and cage-rearing effects on pullets' initial adaptation to multiple-hen cages. Appl. Anim. Behav. Sci. 20:319-333. Craig, J. V., L. L. Ortman, and A. M. Guhl, 1965. Genetic selection for social dominance ability in chickens. Anim. Behav. 13:114-131. Craig, J. V., and N. C. Ramos, 1986. Competitive feeding behavior and social status in multiplehen cages. Appl. Anim. Behav. Sci. 16:69-76. Creel, S. R., and J. L. Albright, 1987. Early experience. Pages 251-268 in: Farm Animal Behavior. Veterinary Clinics of North America: Food Animal Practice. E. O. Price, ed. W. B. Saunders Co., Philadelphia, PA.

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