Subject: Forced Molting of Laying Birds

Introduction

Two animal welfare organizations, United Poultry Concerns and the Association of Veterinarians for Animal Rights, are petitioning the United States Department of Agriculture and the Food and Drug Administration to eliminate the forced molting of laying birds in the United States. Our petition is based on the extreme cruelty of the prolonged food deprivation practice known as forced or "induced" molting, which has been shown to stress the immune function of chickens so severely as to promote a systemic disease condition in the form of Salmonella enteritidis in laying birds. As Salmonella enteritidis has been identified as a major contaminant in shell eggs, and has been scientifically linked to the practice of forced molting, we submit that the cruelty and the contamination are significantly linked so as to warrant the elimination of forced molting in the United States as a means of manipulating egg production and market prices.

The forced molting of laying birds is a farm practice that involves food safety issues, and while our impetus for submitting this petition is that the forced molting of laying birds represents exceptionally cruel and inhumane treatment of these birds, we will present evidence showing that the inhumane practice of withholding food from laying birds for days and even weeks at a time immunologically compromises them so significantly as to render the products derived from these birds a health risk to consumers of their products.

In addition to the evidence linking forced molting and SE in shell eggs, we will present evidence showing that chickens have a complex nervous system and cognitive capacity, and that their ability to suffer from acute and chronic stress, pain, and fear entitles them to relief from the inhumane practice of being deliberately starved. Background on Forced ("Induced") Molting in the United States "Induced moulting is a form of starvation" (Holt, 1992: 165). The U.S. poultry and egg industries use starvation as an economic tool to control and manipulate egg production in commercial laying hens and in hens used for breeding. (Commercial laying hens produce eggs for human consumption, referred to as table or shell eggs. Breeding hens [chickens, turkeys, ducks, etc.] produce the fertile or hatching eggs that hatch into commercial egg-type or meat-type birds.) Forced molting can also include water deprivation, drugs, and artificial light-darkness manipulation designed to shock the bird's system into the desired economic condition.

Prolonged food withdrawal is the most commonly used method of forced molting in the United States. "Methods to induce moulting vary but food and water removal with altered photoperiod are generally the methods of choice" (Holt, 1992:165). The three main methods of forced molting are (1) elimination or limitation of food and/or water; (2) feeding the birds low nutrient rations deficient, for example, in protein, calcium or sodium; (3) and administration of drugs and metals including methalibure, chlormadinone, and progesterone, high levels of iodine, dietary aluminum, and zinc (Bell & Kuney, 201:1992).

In addition, artificial light-dark manipulation is used. For example, a 1-week pre-molt cycle of 16 hours of light/8 hours of dark may be followed by a molt schedule consisting of 8 hours of light/16 hours of darkness (Holt and Porter, 1992). Or a 1-week pre-molt cycle of 24 hours of continuous light is followed by 8 hours of light which is increased on day 20 by .25 hours/week back up to the standard 16-17 hours of continuous light (Kalmbach Feeds). According to food microbiologist James L. Smith of the U.S. Department of Agriculture's Eastern Regional Research Center in Philadelphia, the changing of light patterns to manipulate egg laying results in an increase in Salmonella colonization (Food Chemical News, 5).

Commercial laying hens are sent to slaughter at 17 to 18 months of age (72-80 weeks) or they are kept for another laying cycle, or two (105+ weeks). Their food is removed or nutritionally reduced causing the hormone levels that induce egg production and inhibit feather growth to drop. New feathers push out old ones and the hen stops laying for one or two months instead of three or four. By the fourth day of total starvation, the hen is intended to have lost 25-35 percent of her pre-molt body weight. By the 10th to 14th day, a hen who weighed 3.65 pounds before the molt is intended to weigh 2.56-2.73 pounds (Kalmbach Feeds). In Commercial Chicken Production Manual, North & Bell state that "A fast [sic] of 4 days will usually cause a flock to cease egg production. Longer fasts [sic] of up to 14 days will usually give superior results, but extreme care must be taken to monitor body weight losses and mortality" (1990, 434). A method developed at North Carolina State University includes a week of 24-hour continuous artificial lighting prior to food deprivation for 14 days or even longer (North And Bell, 1990, 439).

Forced molting is an economic practice. The sole purpose of starving laying birds is to extend their "economically useful life." This includes among other things (1) not having to feed the birds during the forced molt and (2) feeding them cheap, inferior rations before and afterward (Bell, 1996: 3-4). Since the 1960s, forced molting ("recycling") reportedly has become the "dominant replacement program for the U.S. table egg industry. Age at flock sale has grown from 75 weeks to 105 weeks for two cycle flocks, and 125+ weeks for three cycle flocks" (Bell, 1995, 38). Under forced molting, the "replacement" flock refers to the same birds--the dwindling number of survivors--used over and over. In 1987 it was estimated that approximately 60 percent of hens nationwide and 90 percent of hens in California were force molted; in 1993 food withdrawal was cited as the primary method of manipulating egg production in the United States (Holt, 1993). The USDA publishes forced molting statistics in Chickens and Eggs under the title "Eggs and Layers on Hand and Eggs Produced by Type, and Forced Molt, 30 Selected States [in a given time- period, e.g., Nov.-Dec. 1994-1995]." These records indicate that at any given time in the United States over six million hens are being systematically starved by the poultry and egg industries. Forced Molting Impairs the Birds' Immune System

"Induced moulting is a form of starvation and a body of literature has shown that dietary restriction can alter humoral and cell-mediated immunity. Overall, deficient diets have been found to diminish humoral immune responses in humans, rats, mice, and chickens. A variety of effects of similar diets on cellular immune responses were also observed" (Holt, 1992:165).

In 1992, U.S. Department of Agriculture immunologist Peter S. Holt reported a USDA study in which white leghorn hens and white rock layer flocks were deprived of food for 14 days. According to Holt, "Food deprivation as a means of inducing a moult in laying hens had a variety of effects on the immune system of the birds. The number of circulating lymphocytes were significantly decreased in the moulted group compared with the control birds." He observed, "Cell-mediated immunity is a very important component of the immune system and any procedure which modifies its effectiveness could have profound effects on the well-being of the bird." His study showed that the "DTH [delayed type hypersensitivity response] to the skin sensitizer DNFB, an indicator of cellular immune responsiveness, was significantly depressed during the moult procedure" (Holt, 1992:170).

Forced molting and indigenous microflora. In a related study, Holt et al., cited the important role of the indigenous intestinal microflora in protecting birds against intestinal colonization by various pathogens. They noted that in addition to depressing cellular immune responsiveness, "Feed withdrawal could potentially have altered the intestinal flora and therefore diminished their protective capabilities" (Holt et al., 1995:62).

Moreover, it is well known that antibiotic/antimicrobial therapy, "whether given specifically for salmonellosis or for other microbial agents, has destructive effects on the normal intestinal microflora, rendering birds highly susceptible to salmonella intestinal colonisation after cessation of therapy" (Fowler, 1990:9). In this picture, forced molting impairs the birds' cellular immune system and disrupts their protective microflora, a combined assault that promotes salmonella infection of the birds. The infection then leads to antibiotic treatment, which further debilitates the birds' immune system. By Impairing the Birds' Immune System, Forced Molting Invites Salmonella enteritidis Colonization

Forced molting is the infliction of a "trauma" (Holt et al., 1994:1268). The physiologic trauma of forced molting promotes disease. Holt reports that "Studies in the authors' laboratory have shown that induced molting significantly depressed the cellular immune response and increased the severity of a concurrent intestinal Salmonella enteritidis (SE) infection."

Molted birds shed significantly higher numbers of SE during the feed removal period than the unmolted group. Histological examination of cecum and colon from molted infected hens revealed inflammation compared with minimal changes in the intestines of unmolted infected hens. Molting, in combination with an SE infection, created an actual disease state in the alimentary tract of affected hens whereas, under normal conditions, little SE-induced morbidity occurred in adult birds. (Holt & Porter, 1992: 1842)

Further examination based on microbiological analysis of early Salmonella enteritidis infection in molted and unmolted hens showed that "induced molting has a profound effect on both intestinal and extraintestinal infection by S. enteritidis, and these effects occur within 24 hr postinfection in the intestine and within 48 hr postinfection in the livers and spleens" (Holt et al., 1995:55).

Withdrawal of feed changes the dynamics of an intestinal infection in hens. In contrast to unmolted hens, in which S. enteritidis was somewhat localized primarily in the cecum, the molted hens exhibited intestinal S. enteritidis infection distributed more along the intestinal tract. In these fasted [sic] hens, the S. enteritidis recovery rate was equivalent for colon, cecum, and feces over the first 72 hr, and at 72 hr even the percent recovery of the challenge organism in the ileum equalled that of the other tissues (compared with 25% recovery in unmolted hens). (Holt et al., 1995:61)

Forced Molting Promotes Horizontal Transmission of Salmonella enteritidis Through the Laying Environment Holt et al. conclude that "feed withdrawal to induce molting has dramatic effects on S. enteritidis infection very early postchallenge" (1995:62). Moreover, the authors cite studies which have shown that in addition to local and systemic colonization by Salmonella enteritidis in force-molted hens, forced molting encourages S. enteritidis organisms to spread to other hens in the confinement environment: "These results correlate well with previous transmission studies in molted hens, in which the S. enteritidis challenge organism was readily transmitted to previously uninfected but contact-exposed hens in adjacent cages" (Holt et al., 1995:62). In Horizontal Transmission of Salmonella enteritidis in Molted and Unmolted Laying Chickens, the evidence showed that "S. enteritidis was transmitted more rapidly to the unchallenged hens in the adjacent cages of molted hens than in unmolted hens, and these molted hens shed significantly more of the organism than unmolted hens [indicating] that induced molting can have substantial effects on transmission of S. enteritidis to uninfected hens, which could affect the overall S. enteritidis status of a flock" (Holt, 1995:239).

Forced Molting and Feces in the Layer Environment.

Molted hens have been shown to amplify Salmonella enteritidis in the layer environment through their feces. In Horizontal Transmission of Salmonella enteritidis in Molted and Unmolted Laying Chickens, Holt states that

although molted hens produce diminished amounts of fecal matter during the period of feed removal compared with fed hens, they still shed large numbers of S. enteritidis into the room environment. The combined effect of acutely susceptible hens exposed to the large numbers of S. enteritidis released into the room resulted in the increased transmission of the organism. Following further rounds of intestinal amplification, the organism readily cycled down the line of susceptible hens. (Holt, 1995:248)

Forced Molting and Rodents in the Laying Environment.

Rodents amplify the spread of Salmonella enteritidis and other pathogens through the concentrated confinement buildings. Forced molting facilitates the multiplication and spread of pathogens through the densely-populated laying houses, via rats and mice. Not surprisingly, starving the hens "could result in the transmission of the [S. enteritidis] organism to uninfected birds . . . and to rodents in the layer houses, which were implicated previously in amplifying a S. enteritidis problem in a layer operation" (Holt et al., 1995:62).

A study published in Poultry Digest (Vol. 51, 1992:16-22) cited by Holt showed that mice can be a significant amplifier of S. enteritidis infection in a layer operation (Opitz, cited in Holt, 1993:416-417). Holt concludes:

Mice can shed large numbers of the organism in their feces (up to 105 S. enteritidis per fecal pellet), and the infection may persist in the mouse population for long periods, even after the poultry houses have been cleaned and disinfected. Mice carrying even low levels of S. enteritidis could conceivably infect hens during molting. Because induced molting has been shown to exacerbate concurrent S. enteritidis infection, resulting in the shedding of large numbers of the organisms, molted hens could serve as a second amplifier of S. enteritidis infection, spreading the organism to other molting hens (and to mice) within a layer operation. (Holt, 1993:416-417)

Stress in Molted Hens Transmits SE Through the Laying Environment

Observing that feed-withdrawal stress in broiler chickens has been shown to increase intestinal numbers of Salmonella enteritidis in the birds, Holt identifies the stress of forced molting as a probable cause of the fact that in his study, Salmonella enteritidis was "transmitted rapidly to uninfected hens when the hens were molted, in contrast to the lower transmission in unmolted hens at the same time. These effects were also observed when a lower challenge dose was used." Accordingly,

The stress of molting thus appears to result in an increase in intestinal numbers of S. enteritidis and the transmission to uninfected hens. . . . Stress has also been shown to cause the reactivation and transmission of infectious laryngotracheitis virus in hens. (Holt, 1995:248)

Forced Molting, Contaminated Feathers and Feather Consumption By Hens Attempting to Cope With Hunger and Starvation

Feathers are composed mainly of the protein, keratin. Amino acid deficiencies such as low arginine content in the food have been indicated as a cause of abnormal feather pecking in confined birds (Vestergaard et al., 1993:1127). Forced-molted hens pluck and consume the feathers of adjacent hens in their effort to reduce the hunger and nutrient deprivation imposed on them. Feathers can become contaminated with salmonellae and remain contaminated for long periods. In the Salmonella-infested forced- molting environment, the spread of the disease to and among the hens appears to be increased by contaminated-feather consumption caused by being starved (Holt, 1995:248). Moreover, the stress and pain of being plucked simultaneously while being starved and helpless further encourages colonization and transmission of the pathogen due to the added assault upon the immune system.

The passivity and virtual shutdown that occurs under these circumstances has been suggested by some animal scientists as an adaptive mechanism reducing the occurrence of long-term suffering. F. Wemelsfelder states more reasonably

It would be conceptually meaningless to assume that such states could in any way come to be experienced by an animal as "normal" or "adapted." Behavioural flexibility represents the very capacity to achieve well-being or adaptation; impairment of such capacity presumably leaves an animal in a helpless state of continuous suffering. (Wemelsfelder, 1991:122)

Being plucked is both stressful and painful. In Physiological and behavioural responses associated with feather removal in Gallus gallus var domesticus [chickens], Gentle and Hunter state

Nociceptors [pain receptors] have been identified in the skin of several avian species and the detailed stimulus- response characteristics of these receptors have been determined in the chicken. The follicular wall of the feather is richly supplied with general somatic afferent (sensory) fibres and nerves are present in the papilla, pulp and feather muscles. . . . The feather is firmly held in the follicle. (Gentle and Hunter, 1990:95).

Forced Molting is Cruel, and the Cruelty and Contamination are Linked

Chickens experience pain, fear and other forms of suffering, trauma, and stress. Pain receptors, thermo-receptors, and physical-impact receptors responsive to noxious (tissue damaging) stimuli have been identified in birds and characterized in chickens. Like mammals subjected to aversive stimuli, chickens show a rapid increase in heart rate and blood pressure, and behavioral changes consistent with those found in mammals including efforts to escape, distress cries, guarding behavior, and passive immobility characteristic of birds and mammals subjected to trauma that continues regardless of the victim's attempts to reduce or eliminate it. Comparing birds' capacity to suffer with that of mammals, Michael J. Gentle states, '[I]t is clear that, with regard to the anatomical, physiological and behavioural parameters measured, there are no major differences and therefore the ethical consideration normally afforded to mammals should be extended to birds" (1992:235).

Chickens have cognitive complexity which increases their capacity to suffer from what is done to them. Cognitive research shows that "the chicken is not an inferior species to be treated merely as a food source" (Rogers, 1995, 13). In every relevant respect, "it is now clear that birds have cognitive capacities equivalent to those of mammals, even primates" (Rogers, 1995, 217).

Forced molting is Conducted in an Environment that Encourages Salmonella enteritidis and Other Pathogens to Colonize and Multiply. As microbiologist John Avens of Colorado State University summarized, Salmonella infection of animals will occur more frequently and affect more individual animals, as concentration of confinement increases" (1987:122). The concentrated confinement of laying hens is such that 97.8 percent of hens laying eggs for human consumption in the United States are in cages so densely packed that the individual 3-to-4-pound bird has only 48 square inches of total living space (Bell, 1995:37; United Egg Producers). So housed, the hen cannot assume a single normal body posture (Baxter, 1994:617). The living conditions under which forced molting is practiced are inherently pathogenic--disease producing. Forced molting abuses an already chronically-stressed bird that has been characterized as "having a complex nervous system designed to form a multitude of memories and to make complex decisions" (Rogers, 1995, 218). According to avian physiologist Lesley J. Rogers:

Chickens in battery cages are cramped in overcrowded conditions. Apart from restricted movement, they have few or no opportunities for decision-making and control over their own lives. They have no opportunity to search for food and, if they are fed on powdered food, they have no opportunity to decide at which grains to peck. These are just some examples of the impoverishment of their environment. Others include abnormal levels of sensory or social stimulation caused by excessive tactile contact with cage mates and continuous auditory stimulation produced by the vocalizing of huge flocks housed in the same shed. Also, they have no access to dustbathing or nesting material. Chickens experiencing such environmental conditions attempt to find ways to cope with them. Their behavioural repertoire becomes directed towards self or cage mates and takes on abnormal patterns, such as feather pecking and other stereotyped behaviours. These behaviours are used as indicators of stress in caged animals. (Rogers, 1995, 219)

Starvation and Fasting Are Not the Same.

Over the last few decades the U.S. poultry and egg industries have developed a euphemistic vocabulary designed to downplay and disguise the realities of forced molting. Whereas a researcher in 1967 appropriately referred to the food deprivation methods of forced molting as "severe starvation methods" (Bell, Feedstuffs July 1, 1967:24), today's industry uses terms such as "pause," "rest," and "fast." These terminological transformations seek to throw a guise of welfare and innocuousness over the fact that the birds are being deliberately starved and that they are enduring trauma and pathological stress as manifested by their body language, vocalizations, immune system breakdown, and increased susceptibility to disease. A rest is not a trauma.

An example of the effort to rationalize forced molting as something other than what it really is appeared in an article in The Journal of Applied Poultry Research, where forced molting was falsely equated with the annual molt of wild birds (Self, 1997:373).

"Anorexia" means loss of appetite or refusal to eat, not food removal. Forced molted hens do not stop eating because they lose their appetite or don't want to eat, but because their food is taken away from them. A visitor to an egg farm in Pennsylvania wrote regarding the first day of a 7-day starvation program, "When the lights came on, the cackling and clucking rose to a cacophony, accompanied by the sound of thousands of beaks pecking on metal" (Geist, 1991:3).

Neither naturally-molting hens nor brooding hens go for a week or two at a time without eating. Indeed, a hen with a clutch of eggs leaves her nest for ten to twenty minutes each day until her chicks are ready to hatch, to forage for food, drink water, defecate, and exercise. Artificially-incubated eggs must be cooled for 15 to 20 minutes a day to match the time the hen is away from her nest. The hen does stay on her nest during the 24 to 48 hours that it takes for her chicks to hatch upon which they go out and search for food. As noted by Mrosovsky and Sherry

While it is presumably possible in theory that the hen is getting hungrier and hungrier as she sits on the nest, a much more elegant and safer solution to the problem would be to lower the set-point [for body fat] and avoid clashes between incubating and eating. Similarly, in the case of hibernators, the motivation to hibernate would have to be very strong to overcome the temptations of food lying right under the animal's nose. (Mrosovsky and Sherry, 1980:839)

Fasting is self-imposed behavior, not food removal. To fast means to abstain from all or certain foods. Fasting is a form of behavior that proceeds from within an individual or a species that is part of a larger purpose or activity that is meaningful to that individual or species, e.g., hibernation, migration, or hatching chicks. In humans, fasting is typically undertaken for perceived health, ethical, or political benefits. It is not something that an individual or a group imposes upon another in any case. A brooding hen is bodily and mentally engaged in a structured, holistic activity that is meaningful for her and bears no resemblance to the alien and frightening experience of being arbitrarily deprived of food. We may go for hours without eating while we are absorbed in a project; however, this is completely different from somebody locking us in our room without food or the prospect of food.

As the article Animal Anorexias explains, when animals fast in nature, fasting is part of their being "engaged in other important activities that compete with feeding" Evidence indicates that "fasting is physiologically different from starvation" (Mrosovsky and Sherry, 1980:840).

Indeed, whereas the brooding hen can be seen to be fully intent upon her "other important activities that compete with feeding," the hen being starved has been stripped without compensation of her only pleasure, virtually her only activity in confinement, which is eating. It is not surprising that whereas animals fasting in nature do not generally suffer from immune system breakdown, disease infestation, and disease transmission as a result or concomitant of their temporary abstention from eating, force-molted hens have been shown to lose their natural immunity and to develop and spread diseases as a result of their being starved. As Holt summarizes in one of his articles, "In conclusion, induced moulting did exert a substantial effect on the immune system of the fasted [sic] hens. . . . Cellular immunity . . . was significantly depressed during food deprivation" (Holt, 1992:173).

Forced molting Should Be Banned in the United States As Was Done in Great Britain in 1987.

Schedule 1 of the Welfare of Livestock Regulations 1994 states that "except in the case of therapeutic or prophylactic treatment, all laying hens shall have access to adequate, nutritious and hygienic feed each day in sufficient quantity to maintain them in good health and to satisfy their nutritional needs, and to adequate fresh drinking water at all times." This provision applies to laying hens kept in battery cages and is a consolidation of requirements previously set out in the Welfare of Battery Hens Regulations 1987 and the Welfare of Livestock Regulations 1990. Similar provisions, in Schedule 4 of the Welfare of Livestock Regulations 1994, apply to broiler breeders (Harris, 1995).

Conclusion

Forced molting is not therapeutic, prophylactic, or humane. It is not a "rest" but the deliberate infliction of physiologic and cognitive trauma and stress. It is so inimical to the well- being of the birds subjected to it that it overwhelms their immune system and encourages them to develop and spread diseases such as Salmonella enteritidis. It is so ethically reprehensible that the arguments used to justify it merely add insult to injury, as in comparing forced molting to life-saving human surgery or to the autonomous act of fasting (Bell, 1996:2). The fact that many people in the world have been condemned to live in substandard housing has actually been used to justify forced molting and other farm animal abuses. Thus, "Living in cramped quarters may not be as comfortable as living in a mansion, but it is considerable [sic] better than the alternative of living in the outdoors and therefore is not rejected arbitrarily" (Bell, 1996:2).

Forced molting epitomizes the link between the cruelty and contamination that characterizes much of the way we treat farm animals in the United States. There is not a single federal law in this country that governs how animals are treated on the farm. This situation needs to change and forced molting is the place to start. In Bell's words, "Because of the perception that the birds are being starved, many countries now prohibit fasting [sic] as a means to initiate a moult" (Bell, 1996:4). We are formally petitioning the United States Department of Agriculture and the Food and Drug Administration to eliminate the forced molting of laying birds in the United States for the reasons set forth in this petition: the forced molting of laying birds is cruel and it causes disease.

References

Avens, J.S. Overview: Salmonella--What's the problem? Third Poultry Symposium Proceedings: Managing for Profit (Fort Collins, CO: Colorado State University, 1987), 119-123.
Baxter, M.R. The welfare problems of laying hens in battery cages. The Veterinary Record 134:614-619. 1994.
Bell, D. The economics of various molting methods. Feedstuffs July 1, 1967: 21+.
Bell, D., and D.R. Kuney. Effect of fasting and post-fast diets on performance in molted flocks. The Journal of Applied Poultry Research 1:200-206. 1992.
Bell, D. Forces that have helped shape the U.S. egg industry: the last 100 years. The Poultry Tribune Sept. 1995:30-43.
Bell, D. Moulting Technologies--Welfare Issues Oct. 1996:1-9.
Food Chemical News. Washington DC. June 6, 1994.
Fowler. N. Competitive exclusion--the way forward? International Hatchery Practice 5.1:5,9. 1990.
Geist, K. The Friendly Vegetarian (Washington DC: Friends Vegetarian Society of North America) 37. 1991.
Gentle, M.J., and L.N. Hunter. Physiological and behavioural responses associated with feather removal in Gallus gallus var domesticus. Research in Veterinary Science 50:95-101. 1990.
Gentle, M.J. Pain in birds. Animal Welfare 1:235-247. 1992.
Harris, J. (Ministry of Agriculture, Fisheries and Food, U.K.) Letter to Farm Animal Welfare Network (U.K.). Aug. 1995.
Holt, P.S. Effects of induced moulting on immune responses of hens. British Poultry Science 33:165-175. 1992.
Holt, P.S., and R.E. Porter. Effect of induced molting on the course of infection and transmission of Salmonella enteritidis in white leghorn hens of different ages. Poultry Science 71:1842-1848. 1992.
Holt, P.S. Effect of induced molting on the susceptibility of white leghorn hens to a Salmonella enteritidis infection. Avian Diseases 37:412-417. 1993.
Holt, P.S., and R.E. Porter. Effect of induced molting on the recurrence of a previous Salmonella enteritidis infection. Poultry Science 72:2069-2078. 1993.
Holt, P.S. Effect of Two Different Molting Procedures on a Salmonella enteritidis infection. Poultry Science 73:1267- 1275. 1994.
Holt, P.S., et al. Microbiological analysis of the earliest Salmonella enteritidis infection in molted and unmolted hens. Avian Diseases 39:55-63. 1995.
Holt, P.S. Horizontal transmission of Salmonella enteritidis in molted and unmolted laying chickens. Avian Diseases 39:239- 249. 1995.
Kalmbach Feeds, Inc. (Upper Sandusky, OH) Egg layer molting program. n.d.
Mrosovsky, N., and D.F. Sherry. Animal anorexias. Science 207:837-842. 1980.
North, M.O., and D.D. Bell. Commercial Chicken Production Manual, 4th ed. (New York: Van Nostrand Reinhold, 1990).
Rogers, L.J. The Development of Brain and Behaviour in the Chicken. (Wallingford, Oxon, U.K.: CAB INTERNATIONAL, 1995).
Self, J. Effects of increased light and added methionine on molted hens. The Journal of Applied Poultry Research 6:373- 380. 1997.
United Egg Producers, Recommended Guidelines of Husbandry Practices for Laying Chickens, n.d.
USDA/NASS, Chickens and Eggs. (Washington DC) Jan. 31, 1996.
Vestergaard, K.S., et al. Feather pecking and chronic fear in groups of red junglefowl: their relations to dustbathing, rearing environment and social status. Animal Behaviour 45:1127-1140. 1993.
Wemelsfelder, F. Animal boredom: do animals miss being alert and active? Applied Animal Behaviour: Past, Present and Future. Ed. M.C. Appleby, et al. (Potters Bar, Herts, U.K.: United Federation for Animal Welfare, 1991), 120-123.

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