The Animal Welfare and Food Safety Issues
Associated With the Forced Molting of Laying Birds
© 2003 United Poultry Concerns, Inc.
The food deprivation practice commonly known as forced or "induced"
molting of laying hens has been shown to induce significant systemic
and infectious disease conditions in these birds. Salmonella
enteritidis [SE], which has been identified as a major contaminant
in shell eggs since the 1980s, has been scientifically linked to
the practice of forced molting, making forced molting both a food
safety and an animal welfare issue. The United Egg Producers Animal
Welfare Advisory Committee summarized in 2000 that “[b]ehavioral
and immune system measures indicate that the welfare of the hen
is compromised when feed withdrawal or restriction is used to induce
a molt” (Armstrong, 2000).
The practice of withholding food from laying hens from five to
twenty-one days at a time, or until they lose 25 percent to 35 percent
of their initial body weight (Webster, 2000:192), is currently done
by 75 percent to 80 percent of the layer industry in the United
States (Bell, 1999, p. 68). This practice has been shown to compromise
the immune function of the birds so severely as to render their
eggs a health risk to consumers as well as compromising the well-being
of the birds. In particular, Salmonella enteritidis (SE) has been
linked to forced molting; however, other pathologic changes in force-molted
hens have also been identified. These changes, which do not normally
occur in naturally molting hens, include a loss of 25 percent or
more of body weight attributed to loss of weight “in body
fat, feathers, liver tissue, musculature and skeleton” (Bell,
1996, p. 4). In studies, force-molted hens “shed significantly
higher numbers of SE during the feed removal period than the unmolted
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. (Holt & Porter, 1992:1842)
The USDA’s Food Safety and Inspection Service (FSIS) has
acknowledged that “public health concerns are raised by highly
stressful forced molting practices [which] lead to increased shedding
of Salmonella enteritidis (Se) by laying hens subjected to
these practices” (Stolfa, 1998). In 1999, a General Accounting
Office Report on food safety identified forced molting as a primary
factor associated with increased levels of Salmonella enteritidis
in commercial laying flocks (GAO, 1999, p. 25), and Egg Industry
magazine observed that “[r]educed feed and water intake is
the most detrimental and universal aspect of disease” in laying
hens (Beckman & Grieve, 1999, p. 10).
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 food deprivation as an economic
tool to manipulate egg production in commercial laying hens and
in male and female birds used for breeding of both egg-type and
meat-type birds (North & Bell, pp. 433-452). Prolonged food
withdrawal with light-dark manipulation (“altered photoperiod”)
is the most common method of forced molting in the United States
(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 in protein, calcium or sodium;
(3) and administration of drugs, hormones, and metals including
methalibure, chlormadinone, and progesterone, high levels of iodine,
dietary aluminum, and zinc (Bell & Kuney, 1992:201). Bell reports
that “[o]ver the years, most flock managers have eliminated
the removal of water and have increased the number of days of feed
removal” (1996, p. 4).
In standard forced molting practice, artificial light-dark manipulation
accompanies the removal of food from the birds. 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 increases Salmonella colonization
of laying hens (Food Chemical News, p. 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 10th to 14th day of total food deprivation, a hen who weighed
3.65 pounds before the molt weighs 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, p. 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 longer (North & Bell, 1990, p. 439).
Forced molting is designed to extend the "economically useful
life" of laying flocks in order to “reduce the cost of
a replacement program,” and to regulate market prices (North
& Bell, 1990, p. 445; Bell, 1996, p. 3; Smith, 1997, p. 8).
The economic benefits include not having to feed the birds during
the molt and feeding them cheap, inferior rations before and after
the molt (Bell, 1996, pp. 3-4). These savings, based on egg value
minus feed cost, explain why the majority of the U.S. egg industry,
unburdened as it has been by either legal or ethical considerations,
has opted to starve hens to make them molt them rather feed them
an altered diet that is capable of producing comparable results
(Smith, 2002, pp. 8, 27). Since the 1960s, forced molting ("recycling")
has been the dominant method of flock replacement for the U.S. table
egg industry. In forced-molting terminology, "replacement flock”
refers to the same birds--the dwindling number of survivors--used
over and over. According to Bell, at any given time in the United
States, approximately 70 million laying hens out of a total of 250
million hens are being force-molted or have been force-molted as
many as three times, “with disposal ages ranging from 75 to
140 weeks of age” (Bell, 1999, p. 68).
Forced Molting Impairs Birds' Immune Systems
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. He wrote that "[f]ood
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." Observing that "[c]ell-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, Holt found 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).
Depressed Immunity Invites SE Colonization of Force-Molted
Forced molting is the infliction of a "trauma" that encourages
disease (Holt et al., 1994:1268). According to Holt, "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." Microbiological analysis of early Salmonella
enteritidis infection in molted and unmolted hens has shown
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 equaled that of the other
tissues. (Holt et al., 1995:61)
Forced Molting Promotes Transmission of SE Via Stress,
Rodents, and Feces
In addition to encouraging SE colonization of individual hens,
forced molting encourages SE organisms to spread to other hens in
the confinement environment (Holt et al., 1995:62). SE 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). One reason
for these “substantial effects” on SE transmission is
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)
Another reason is rodents. Studies have shown mice to be significant
amplifiers of S. enteritidis infection in layer operations.
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)
Still another reason for the “substantial effects”
of forced molting on SE transmission is feces.
[A]lthough 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)
Contaminated Feather Consumption By Forced-Molted Hens
Feathers are mainly composed 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). Force-molted hens pluck and consume
the feathers of adjacent hens in a desperate effort to reduce their
hunger. Feathers contaminated with Salmonellae remain contaminated
for long periods. In the forced-molting environment, the spread
of Salmonella enteritidis through flocks appears to be
increased by hens consuming the contaminated feathers of adjacent
birds (Holt, 1995:248). The hens must thus endure not only hunger
and body depletion but the stress and pain of being plucked by their
equally desperate cagemates. The pain of plucking is explained by
Gentle and Hunter:
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)
Behavioral Indicators of Suffering in Force-Molted Hens
Comparing a bird’s capacity to suffer with that of a mammal,
Gentle states that “with regard to the anatomical, physiological
and behavioural parameters measured, there are no major differences
“ (1992:235). 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 animals subjected to trauma that continues regardless of their
attempts to reduce or eliminate it (Gentle, 1992).
Chickens deprived of food show pronounced suffering. Contrary to
assertions that hens do not suffer in being force molted, Duncan
and Mench maintain that the evidence presented “does suggest
[T]he increased aggression suggests severe frustration and the
increased non-nutritive pecking, some of which was stereotyped,
suggests severe frustration and extreme hunger, and the reduced
activity suggests debilitation (PoultryScience, 2000:934).
As further evidence of animal suffering, they cite molting results
from 353 U.S. flocks during 1997 and 1998, which showed that “mortality
typically doubled during the first week of molt, then doubled during
the second week.”
A force-molting study published in Applied Animal Behaviour
Science showed similar results. Observing that “the hens
were highly motivated to perform feeding behaviour and were prevented
from doing so” by the researchers, and that “t]he different
types of behaviour pattern which are typical during frustration
are displacement movements, escape behaviour, aggression and stereotypies,”
Aggrey, et al. wrote that “the hens were hungry and were looking
for food,” and “kept pecking the empty feeding trough,
walls and floor.” They noted “an increase in negative
social interaction,” stating that the “increase in negative
social interaction may inflict pain which is very important in the
evaluation of the wellbeing of the hens.” While noting that
the frustration behavior appeared to be less in caged hens than
in hens on a wire floor system, the researchers cautioned that cage
constraints which suppress normal animal behavior are “by
no means better for animals. Cages can only allow pseudo-behaviour
and therefore cannot be judged as adequate for hens” (Aggrey,
et al., 1990:103).
Chickens’ cognitive complexity may increase their ability
to suffer in being force molted. Cognitive research shows that "the
chicken is not an inferior species to be treated merely as a food
source" (Rogers, 1995, p. 213), and that in all relevant respects,
"birds have cognitive capacities equivalent to those of mammals,
even primates" (p. 217). Forced molting subjects an already
overstressed bird, characterized as "having a complex nervous
system designed to form a multitude of memories and to make complex
decisions," to significantly more stress than she is already
being forced to cope with (p. 218).
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, p. 219)
Starvation and Fasting Are Not the Same.
"Anorexia" means loss of appetite or refusal to eat,
not food removal. Force-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, p. 3).
Naturally-molting hens do not go for days and weeks without eating,
while 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. Mrosovsky and Sherry observe that
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 originates within
an individual or a species as part of a larger purpose or activity
that is meaningful to that individual or species, e.g., hibernation,
migration, or hatching chicks. A brooding hen is engaged in normal
species behavior that is meaningful for her and has no resemblance
to the frightening experience of being arbitrarily deprived of food.
Mrosovsky and Sherry summarize that when animals fast in nature,
fasting is part of their being "engaged in other important
activities that compete with feeding" and that evidence shows
fasting to be “physiologically different from starvation"
Whereas a brooding hen and a naturally-molting hen are fully intent
upon “other important activities that compete with feeding,"
the hen being starved in confinement has been stripped, without
compensation, of her only pleasure, virtually her only activity
in confinement, which is eating. Moreover, and most significantly,
animals fasting in nature do not generally suffer from immune system
breakdown and disease, whereas force-molted hens do. In force-molted
hens, cellular immunity is “significantly depressed during
food deprivation," and SE infection and transmission are increased
USDA Summary of Disease Causality Associated with Forced
Holt summarized the causality between the withholding of food,
immunosuppression, and diseases in hens including, but not confined
to, Salmonella enteritidis, in a review paper obtained by United
Poultry Concerns through a Freedom of Information Act request to
the USDA, June 3, 1999 (Marquis, 1999). This undated 13-page paper,
“Impact of Induced Molting on Immunity and Salmonella enteritidis
Infection in Laying Hens,” cites studies showing that deficient
diets diminish cell-mediated immunity in mammals and birds, and
that a concurrence of systemic and infectious disease conditions
likewise occurs in force-molted hens (Holt, n.d.). According to
Holt, to cite key points:
- “An altered immune response was also observed in birds
subjected to induced molting through feed withdrawal” (p.
- “Total peripheral blood lymphocyte numbers were significantly
decreased in molted birds” (p. 3).
- “Elevated levels of serum corticosterone were detected
during times of stress [in birds and mammals in other studies].
. . . A similar elevation in this stress hormone was noted in
hens subjected to feed removal . . . which may be responsible
for observed effects on immunity during an induced molt”
- “Protection [of internal organs from pathogens] is mediated
by effector T cells and by a battery of hormone messages called
lymphokines which regulate the intensity of the immune response
and define what effector cells will play a role in the protection.
Breaching this immunity can dramatically alter its ability to
protect the host against infection” (p. 4).
- “The discovery [was] that the immune system in molted
hens was compromised” (p. 4).
- “The potential problems associated with the presence of
S. enteritidis in the flock environment therefore become
exacerbated when birds are exposed to a stress situation such
as feed removal” (p. 5).
- “Stress situations can reactivate a previous infection
. . . and feed withdrawal to induce a molt can also cause the
recurrence of a previous S. enteritidis infection”
- “[R]ecrudencence of infection was observed significantly
more often in molted birds. [T]hese birds shed significantly more
S. enteritidis and more readily transmitted the organism
to previously uninfected, but contact-exposed hens” (p.
- “The molted hens also produced more eggs contaminated
with the organism” (p. 5).
- “[I]ntestinal spirochete infections were more severe
in molted hens, indicating that, similar to what was observed
for S. enteritidis, molting upset the equilibrium normally
attained between the host and that parasite” (p. 7).
- “Perhaps more telling is the study conducted by the S.
enteritidis Pilot Project in Pennsylvania (U.S. Department of
Agriculture 1995) which showed that the production of eggs contaminated
with S. enteritidis increased during the molt. These
data prompted the authors to categorize molting as a risk factor
for S. enteritidis” (p. 7).
In their Interpretive Summary of the “The Effects of Induced
Molting on the Severity of Acute Intestinal Infection Caused by
Salmonella Enteritidis,” Holt and his colleagues conclude:
These results are important to the layer industry since they
show that a prevalent industry procedure has a substantial effect
on the severity of an SE infection and these effects are observed
early in the disease process. Also, many organisms infect poultry
and if molting has such rapid effects on an infection by SE, it
is very possible that it could have similar effects on infection
by other poultry disease agents. (Macri, et al., 1998:1)
Forced Molting Has Been Widely Condemned and Abandoned
The Canadian Veterinary Medical Association and the Scientific
Veterinary Committee for the European Union have condemned forced
Food deprivation, the most common method of forcing a molt, was
banned in the United Kingdom and then in the European Union as both
cruel and unsafe. According to the UK Welfare of Livestock Regulations
(1994), "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."
The U.S. Department of Agriculture’s Food Safety and Inspection
Service, the United Egg Producers Animal Welfare Advisory Committee,
Consumers Union, Center for Science in the Public Interest, and
other consumer groups have requested the forced molting be stopped.
In 2000, the McDonald’s Corporation banned the purchase of
eggs from force-molted hens followed by Burger King and Wendy’s
International in 2001.
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 systems
and encourages them to develop and spread diseases such as Salmonella
enteritidis. Arguments used to justify forced molting merely
add insult to injury, as in comparing forced molting to life-saving
surgery or to the autonomous act of fasting (Bell, 1996, p. 2).
Forced molting epitomizes the link between the cruelty and contamination
that characterizes much of the way we treat farmed animals in the
United States. There is not a single federal law in this country
that governs how animals are treated on the farm. The moral and
legal abandonment of these animals needs to change, and condemnation
of forced molting by organizations and associations that profess
an animal welfare objective as an integral part of their mission
is a logical place to begin. The practices involved in forced molting
violate humane standards of animal husbandry as well as the anti-cruelty
laws of most states, which require the provision of sustenance for
As the voice of the veterinary profession in the United States,
the American Veterinary Medical Association has a responsibility
to its members, the public, and the animals it serves to condemn
forced molting by food deprivation and restriction, and to endorse
husbandry practices that truly protect the health and well-being
of both farmed animals and the consumers of farmed animal products.
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March 31, 2000.
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