Laying Hen Behavior 2. Cage Type Preference and Heterophil
to Lymphocyte Ratios1
J. J. Elston,2 M. Beck,3 M. A. Alodan, and V. Vega-Murillo
Department of Animal Science, University of Nebraska-Lincoln, Lincoln, Nebraska 68583-0908
chose neither. The length of time required to choose one
compartment over the other did not differ in either experiment (P = 0.29; P = 0.76). In Experiment 3, tests were
videotaped from 0830 h to 1330 h, and tapes were scored
for time spent in each compartment. Birds were observed
to spend more time in open- compared with solid-sided
compartments (P = 0.02). To assess stress level of birds
exposed to each type of enclosure, blood was collected
from 24 commercial Hy-Line W36 hens housed long-term
in either open (n = 12) or solid (n = 12) cages, and heterophil:lymphocyte (H:L) ratios were determined. Birds in
solid cages had higher H:L ratios than did birds in open
cages (P = 0.02), indicating a greater stress response. These
data would suggest that hens may prefer greater visual
access to their surroundings afforded by open cages.
ABSTRACT Studies were conducted to determine hen
preference for and stress response to cage type. By using
a plywood (1.25 cm) test apparatus with open- and solidsided compartments and a plexiglass divider at the entrance for controlling passage, birds (n = 20) were evaluated as to their choice of compartment after training and
acclimation. For each test, after training, an individual
bird was placed in the start box and given 1 min to acclimate before making a choice. The experiment was repeated after rotating the apparatus 180°. In Experiment
1, the open-sided compartment was chosen by 45% of the
hens, and the solid-sided compartment by 25% (P = 0.02);
30% chose neither. In Experiment 2, the compartment
with open sides was chosen by 70% of the hens, and that
with solid sides was chosen by 15% (P = 0.004); 15%
(Key words: laying hen, cage types, preference testing, behavior)
2000 Poultry Science 79:477–482
found among types of behaviors or among the frequency
of certain behaviors of hens housed in open vs. solidsided cages (Elston and Beck, 1997). However, reports
from some producers (S. E. Scheideler, unpublished data)
and observations from our own laboratory indicate that
hens housed in open-sided cages exhibit “flighty” behavior. These observations would suggest that a higher level
of excitability or lack of calmness is common in birds
housed in open-sided cages.
Although the question of motivation is not addressed,
preference testing is one way in which an animal’s perception of its environment can be assessed (Hughes, 1975;
Dawkins, 1983; Lindberg and Nicol, 1996). Information
derived from preference tests can then be used when
determinations are made about cage design (Hughes and
Black, 1973; Dawkins, 1985) or to evaluate and improve
bird comfort (Gonyou, 1994).
Many physiological variables have been assessed as
indicators of stress. Chief among these variables are circulating corticosterone concentrations and heterophil:lymphocyte (H:L) ratios (Gross and Siegel, 1983). Because of
the relatively low variability associated with the H:L ratio
response, it is considered to be the more appropriate
measure of long-term stress (Gross and Siegel, 1983).
INTRODUCTION
Scientists have shown that the well-being of the domestic fowl can play a significant role in production; hens
subjected to stressful situations lay fewer eggs (Mashaly
et al., 1984; Hughes et al., 1986; Solomon et al., 1987).
Considerable variation in size, shape, floor type, and construction exists among cages from different manufacturers (North and Bell, 1990). One substantial difference that
can exist among cages is in the type of side partitions
that they possess. Few studies have been conducted to
compare the performance of hens in open-wire cages (predominately US) and solid metal cages (common in Europe) (D. D. Bell, personal communication) cages. Nevertheless, the results have been contradictory and have
failed to establish one type of cage construction as superior to the other either in terms of production (Ramos et
al., 1986; Cunningham and Gvaryahu, 1987) or well-being
(Tauson, 1995). In an earlier study, no differences were
Received for publication March 18, 1999.
Accepted for publication December 8, 1999.
1
Published as Journal article 12529, Agricultural Research Division,
University of Nebraska-Lincoln, Lincoln, NE 68583-0708.
2
Current address: Department of Wildlife Science, Texas A & M
University, Kingsville, TX 78364.
3
To whom correspondence should be addressed: [email protected].
Abbreviation Key: H:L = heterophil:lymphocyte.
477
478
ELSTON ET AL.
FIGURE 1. Preference test apparatus with a hen in the open-sided
cage. Start boxes are located opposite each other at right angles to the
two test compartments.
The objectives of this study were to determine whether
laying hens prefer open- or solid-sided cages when given
the choice and which cage type elicits the greatest physiological stress response, as measured by H:L ratio.
MATERIALS AND METHODS
Preference Test Studies
Twenty Hy-Line W36 White Leghorn laying hens were
used in this series of experiments. All hens came from a
flock of approximately 45 birds that had been housed
together in a floor pen from 56 to 67 wk of age when the
study was conducted. Birds had ad libitum access to water
and a corn-soybean diet (2,898 kcal ME/kg; 16% CP).
Temperature was maintained at 25 to 27 C, and the photoperiod was a 16 h light:8 h darkness cycle.
The test apparatus was constructed of 1.25-cm plywood
and had an open-sided compartment made of wire and
plywood and a solid-sided compartment made only of
plywood; the two were opposite each other and were
connected by a solid-sided runway (Figure 1). The solidsided compartment was painted with flat aluminum paint
to simulate the metal sides of industry cages, and paint
was allowed to dry thoroughly until no odor was detectable to observers. Each compartment measured 50.8 × 50.8
× 60.96 cm and was equipped with a plexiglass divider
at the entrance that could be lifted to allow entry. The
plexiglass allowed the birds to see the different environments. Birds gained access to either side from one of two
start boxes, also equipped with plexiglass dividers, that
led to a small runway between the two compartments.
Hens were alternated between boxes during testing to
avoid directional bias. In the first and second trials, birds
were tested during the late morning and throughout the
afternoon, during periods of no oviposition to avoid any
effect of egg laying on choice.
Birds were tested individually, according to the method
described by Dawkins (1978), in which each bird received
four training trials in succession prior to testing. Birds
were randomly assigned a training sequence (e.g., open,
solid, solid, open). In training sessions, birds were first
placed in the start box and given 1 min to acclimate before
the plexiglass divider was lifted. Upon lifting the divider,
birds were given 5 min to move into the appropriate
compartment on their own, but if they did not, they were
given a gentle push (Lindberg and Nicol, 1996). Once the
bird entered the required compartment, the plexiglass
divider was brought down, and the bird remained there
for 5 min. This procedure was repeated for the other
compartment, so that each bird experienced both cage
types equally. Testing occurred immediately following
training, except that birds had access to both compartments simultaneously and, thus, could make a choice. The
bird was required to remain in its chosen compartment for
a total of 5 min before that cage type was recorded as the
bird’s choice. If the bird wandered out of that particular
compartment in less than 5 min, it was not recorded as
a choice. Latency to choice was considered to be the length
of time from removal of the plexiglass divider until entry
by the hen into the chosen environment. The experiment
was repeated after the apparatus was rotated 180° to
ensure that choice was not influenced by other visual cues
outside the compartment. Each bird was thus tested twice.
The third experiment was carried out to determine
long-term preference by hens for each environment. Birds
were tested individually, with one bird tested per day.
Individual hens were placed in the runway of the apparatus at 0830 h and were videotaped for 5 h. Plexiglass
dividers remained lifted to allow for free passage during
the test. Each compartment contained one bottle waterer
and 100 g of feed. Tapes were scored for the amount of
time (in minutes) that a bird spent in each compartment.
H:L Ratios
Blood samples were collected from 24 45-wk-old HyLine W36 White Leghorn laying hens; 12 samples from
hens housed for a long term in open-sided cages and 12
from hens housed equally long in solid-sided cages. All
birds originated from the same commercial flock and
were housed in either open-sided cages (nine birds per
cage, 378.49 cm2 of floor space per bird) at a commercial
production facility in Nebraska or in commercial solidsided cages (six birds per cage, 409 cm2 of floor space
per bird) within the Poultry Research Complex at the
University of Nebraska-Lincoln. Birds in both facilities
were fed a standard corn-soybean diet (2,898 kcal ME/
kg; 16% CP). Environmental temperature was consistent
between the two facilities at approximately 25 C; and
lighting regimes were also similar with a 16 h light:8 h
darkness cycle each day.
One blood sample was collected from each of 12 hens
per cage type. Because of distance between the two facilities, blood was obtained from birds in open-sided cages
on one day and from birds in solid-sided cages on the
CAGE TYPE PREFERENCE IN HENS
479
following day; time of day for sampling was kept constant. Birds were chosen at random and removed from
the cage, and 1-mL blood samples from the brachial vein
were collected as quickly as possible into heparinized
syringes. Time of handling was minimized for each bird
to avoid creating additional stress and was kept as constant as possible between birds to reduce variability. One
drop of blood from each individual sample was placed
on duplicate glass microscope slides and was smeared
with the canted edge of a second slide. After drying, the
slides were stained using a Leukostat stain.4 Heterophils
and lymphocytes were counted at 1,000× (oil immersion
lens) until a total of 100 cells per slide had been examined;
of the 100 cells, numbers of heterophils and lymphocytes,
respectively, were averaged for all hens within cage type.
Mean H:L ratios were determined by dividing the number
of heterophils by the number of lymphocytes for each
slide and then averaged for all hens within cage type.
Statistical Analysis
In the first and second preference test experiments,
training and test choice date were analyzed by a chisquare test (SAS Institute, 1995). Latency to choice data,
third preference test data, and H:L ratios were analyzed
with a one-way ANOVA using PROC GLM (SAS Institute, 1995). Differences were computed from least
squares means.
RESULTS
Preference Test
During the training sessions for the two short-term
preference test experiments, birds showed a preference
for the open-sided compartment more often (P = 0.001)
than for the solid-sided one, even though passage into
that compartment was prevented by a plexiglass divider;
these training session data are not shown.
In the first preference test experiment (Figure 2), the
open-sided compartment was chosen 9 out of 20 times
(45%), and the solid-sided compartment was chosen 5
out of 20 times (25%) (P = 0.02). Six birds (30%) chose
neither compartment and remained in the runway. The
latency of response for hens in choosing either compartment was not different (P = 0.29). In the second test experiment (Figure 3), hens showed a stronger preference (14
out of 20; 70%) whereas the solid-sided compartment was
chosen only 3 out of 20 times (15%) (P = 0.004). Three
birds (15%) chose neither compartment. Again, latency
of response did not differ (P = 0.76).
In the long-term experiment (Figure 4), birds chose to
spend more time in the open-sided compartment (P =
0.02). On average, birds spent 130 min in the open-sided
compartment compared with 72.9 min in the solid-sided
4
Fisher Diagnostics, Pittsburgh, PA 15230.
FIGURE 2. Choice by Hy-Line hens for the open-sided compartment
or the solid-sided compartment during Experiment 1 of the preference
test (percentage of hens making choice; top) and latency to choice, in
minutes (bottom). Letters above bars that are different indicate that the
open-sided cage was chosen more often than the solid (P = 0.02). Latency
to choice did not differ (P = 0.29).
compartment. Birds spent an average of 97.1 min in the
runway of the apparatus.
H:L Ratios
Mean heterophil and lymphocyte counts and H:L ratios
are presented in Table 1. Birds housed in solid-sided cages
generally had higher H:L ratios than birds housed in
open-sided cages (P = 0.02). This result indicated that
480
ELSTON ET AL.
FIGURE 4. Time (in minutes) Hy-Line hens spent in the open-sided
compartment, the solid-sided compartment, and the runway during
Experiment 3 of the preference test. Letters above the bars indicate that
hens spent more time in the open-sided cages (P = 0.02).
FIGURE 3. Choice of Hy-Line hens for the open-sided compartment
or the solid-sided compartment during Experiment 2 of the preference
test (percentage of hens making choice; top) and latency to choice, in
minutes (bottom). Letters above bars that are different indicate that the
open-sided cage was chosen more often than the solid (P < 0.05). Latency
to choice did not differ (P = 0.79).
open-sided cages were less stressful to the hens than were
solid-sided cages.
DISCUSSION
The results of these studies show that the open-sided
cages may be a more effective form of housing for laying
hens. Like all domestic animals, laying hens are highly
social (McGlone, 1990; Stricklin and Gonyou, 1995), so
that separation from conspecifics becomes potentially
stressful (Grandin, 1993). Banks (1982) reports that secluding individuals from others of their own species can bring
about abnormal behavior. Mench (1992) reports that
many studies have found that domestic hens prefer to be
near conspecifics and that behavioral patterns portraying
comfort are more frequent in the presence of conspecifics.
Although birds are housed together in solid-sided cages,
visual access to birds in surrounding cages is somewhat
impaired and may lead to a sense of isolation.
The results of the preference tests seem fairly conclusive; however, they should not be misinterpreted. Preference tests can be somewhat limiting, and one must be
careful not to assume that denying an animal its preferred
environment causes it to suffer (Mench, 1992). Dawkins
(1978) found that even though hens showed a preference
for larger cages over smaller cages and grass floors over
wire floors, they chose to move into a smaller cage with
a grass floor rather than a large cage with a wire floor.
Dawkins (1978) concluded from this that cage size may
not be the primary factor affecting a bird’s choice but
TABLE 1. Relative numbers of circulating heterophils and
lymphocytes per 100 cells in Hy-Line birds housed
in open- and solid-sided cages
Cage type
Heterophils
(no./100 cells)
Lymphocytes
(no./100 cells)
Ratio
Open
Solid
8.92 ± 4.795
15.58 ± 6.9211
91.08 ± 4.795
84.42 ± 6.9211
0.1008a ± 0.0231
0.1799b ± 0.0231
1
a,b
Values within columns with different superscripts are different; P
= 0.02.
1
Values are expressed as mean ± SEM.
481
CAGE TYPE PREFERENCE IN HENS
that other features of the cage may be important for its
desirability to the hen.
In the first and second preference test experiments, hens
were tested during periods of no oviposition, because
oviposition could have affected choice. Appleby (1986)
reported that oviposition and nesting behavior are synchronized, and Wood-Gush et al. (1978) reported that
from an evolutionary standpoint, concealment, safety,
and other perceptions conducive to improved hatchability are a result of nesting behavior in birds. Because modern commercial hens lay their eggs without ever experiencing a nest box, it is uncertain whether these elements,
which perhaps seem intuitively desirable, are in fact important at all. Certainly, the privacy feature appears not
to be important at other times of the day. Cages with
solid sides obstruct the view on both sides and the top,
limiting visual access to surroundings. For animals that
are social by nature, limiting the ability to observe birds
in neighboring cages could create a sense of isolation.
The H:L ratio has been found to be a successful indicator of stress (Gross and Siegel, 1983; Gross, 1990; Maxwell
et al., 1992; Al-Murrani et al., 1997). A number of studies
have used the H:L ratio for assessing stress in birds (Gross
and Siegel, 1983, 1985; McFarlane and Curtis, 1989; Spinu
and Degen, 1993; Hester et al., 1996; Al-Murrani et al.,
1997). In the avian, heterophils and lymphocytes are more
responsive to stressors than are the other leukocytes, making their differential response less difficult to detect than
differences among the others (Maxwell et al., 1992). In
this study, the lower H:L ratio in birds housed for a long
term in open-sided cages would suggest a response to a
less stressful environment.
Although the H:L ratios in this study were significantly
different from each other, overall percentages were
clearly within normal range. The average number of heterophils in the adult female White Leghorn is approximately 13.3 per 100 cells, and the average number of
lymphocytes is approximately 76.1 (Sturkie and Griminger, 1986), which gives an H:L ratio of 0.1748, and is
comparable to the ratios found in this study and to those
in control birds from other studies (Gross and Siegel,
1983, 1985; McFarlane and Curtis, 1989; Spinu and Degen,
1993; Hester et al., 1996; Al-Murrani et al., 1997). It appears
that cages per se may not be particularly stressful. Nevertheless, cage type may have elicited a differential response. There were no other obvious factors identified
as major stressors in the two environments. The birds
originated from the same genetic stock and were of the
same age. Furthermore, diet and management were comparable.
Because H:L ratios were relatively low for both cage
types, the battery cage system may serve well as the
primary form of housing for laying hens. However, because hens in open-sided cages had significantly lower
H:L ratios, it may be necessary to include open sides as
a predominant feature when manufacturing an ideal cage.
To accommodate hen preference for an open-sided cage
and to realize the benefit that solid sides have on preserving feather cover (Tauson, 1995), manufacturers might
consider designing cages in which the side partitions are
solid on the bottom half and open on the top half. Most
of the hen’s body would thus be protected from abrasion
by the smoothness of the solid sides in the lower half of
the cage, whereas her visual access to birds outside of
her own cage would not be impaired.
In summary, laying hens preferred cages that have an
open side, and because H:L ratios were increased in the
hens housed in solid-sided cages, it appears that this cage
type may increase stress.
ACKNOWLEDGMENTS
The authors thank L. Robeson for apparatus construction and video set up, C. MacFarland for local assistance,
K. Peterson for manuscript preparation, and J. Swanson
and D. Leger for critical review of the manuscript.
REFERENCES
Al-Murrani, W. K., A. Kassab, H. Z. Al-Sam, and A.M.K. AlAthari, 1997. Heterophil/lymphocyte ratio as a selection criterion for heat resistance in domestic fowls. Br. Poult. Sci.
38:159–163.
Appleby, M. C., 1986. Hormones and husbandry: Control of
nesting behavior in poultry production. Poultry Sci.
65:2352–2354.
Banks, E. M., 1992. Behavioral research to answer questions
about animal welfare. J. Anim. Sci. 54:434–446.
Cunningham, D. L., and G. Gvaryahu, 1987. Effects on productivity and aggressive behavior of laying hens of solid versus
wire cage partitions and bird density. Poultry Sci. 66:1583–
1586.
Dawkins, M., 1978. Welfare and the structure of a battery cage:
Size and cage floor preferences in domestic hens. Br. Vet. J.
134:469–475.
Dawkins, M. S., 1983. Cage size and flooring preferences in
litter-reared and cage-reared hens. Br. Poult. Sci. 24:177–182.
Dawkins, M. S., 1985. Cage height preference and use in batterykept hens. Vet. Rec. 116:345–347.
Elston, J. J., and M. M. Beck, 1997. Cage type and strain affect
behavior of laying hens. Poultry Sci. 76(Suppl. 1):17. (Abstr.).
Gonyou, H. W., 1994. Why the study of animal behavior is
associated with the animal welfare issue. J. Anim. Sci.
72:2171–2177.
Grandin, T., 1993. Teaching principles of behavior and equipment design for handling livestock. J. Anim. Sci. 71:1065–
1070.
Gross, W. B., 1990. Effect of exposure to a short-duration sound
on the stress response of chickens. Avian Dis. 34:759–761.
Gross, W. B., and H. S. Siegel, 1983. Evaluation of the heterophil/
lymphocyte ratio as a measure of stress in chickens. Avian
Dis. 27:972–979.
Gross, W. B., and P. B. Siegel, 1985. Effects of initial and second
periods of fasting on heterophil/lymphocyte ratios and body
weight. Avian Dis. 30:345–346.
Hester, P. Y., W. M. Muir, J. V. Craig, and J. L. Albright, 1996.
Group selection for adaptation to multiple-hen cages: Hematology and adrenal function. Poultry Sci. 75:1295–1307.
Hughes, B. O., 1975. Spatial preference in the domestic hen. Br.
Vet. J. 131:560–564.
Hughes, B. O., and A. J. Black, 1973. The preference of domestic
hens for different types of battery cage floor. Br. Poult. Sci.
14:615–619.
Hughes, B. O., A. B. Gilbert, and M. F. Brown, 1986. Categorization and causes of abnormal egg shells: Relationship with
stress. Br. Poult. Sci. 27:325–337.
482
ELSTON ET AL.
Lindberg, A. C., and C. J. Nicol, 1996. Space and density effects
on group size preferences in laying hens. Br. Poult. Sci.
37:709–721.
Mashaly, M. M., M. L. Webb, S. L. Youtz, W. B. Roush, and H.
B. Graves, 1984. Changes in serum corticosterone concentration of laying hens as a response to increased population
density. Poultry Sci. 63:2271–2274.
Maxwell, M. H., P. M. Hocking, and G. W. Robertson, 1992.
Differential leucocyte responses to various degrees of food
restriction in broilers, turkeys and ducks. Br. Poult. Sci.
33:177–187.
McFarlane, J. M., and S. E. Curtis, 1989. Multiple concurrent
stressors in chicks. 3. Effects on plasma corticosterone and
the heterophil:lymphocyte ratio. Poultry Sci. 68:522–527.
McGlone, J. J., 1990. Potential for improving animal health by
modulation of behavior and immune function. Adv. Vet. Sci.
Comp. Med. 35:307–315.
Mench, J. A., 1992. The welfare of poultry in modern production
systems. Poult. Sci. Rev. 4:107–128.
North, M. O., and D. D. Bell, 1990. Pages 315–330 in: Commercial
Chicken Production Manual. 4th ed. Van Nostrand Reinhold,
New York, NY.
Ramos, N. C., K. E. Anderson, and A. W. Adams, 1986. Effects
of type of cage partition, cage shape, and bird density on
productivity and well-being of layers. Poultry Sci. 65:2023–
2028.
SAS Institute, Inc., 1995. SAS/STAT User’s Guide. SAS Institute,
Inc., Cary, NC.
Solomon, S. E., B. O. Hughes, and A. B. Gilbert, 1987. Effect of
a single injection of adrenaline on shell ultrastructure in a
series of eggs from domestic hens. Br. Poult. Sci. 28:585–588.
Spinu, M., and A. A. Degen, 1993. Effect of cold stress on performance and immune responses of Bedouin and White Leghorn hens. Br. Poult. Sci. 34:177–185.
Stricklin, W. R., and H. W. Gonyou, 1995. Housing design based
on behavior and computer simulations. Pages 94–103 in: Animal Behavior and the Design of Livestock and Poultry Systems. Northeast Regional Agricultural Engineering Service,
Ithaca, NY.
Sturkie, P. D., and P. Griminger, 1986. Body fluids: Blood. Pages
102–109 in: Avian Physiology. 4th ed. P. D. Sturkie, ed.
Springer-Verlag, New York, NY.
Tauson, R. K., 1995. Comparative evaluation and development
of housing systems for laying hens. Pages 83–93 in: Animal
Behavior and the Design of Livestock and Poultry Systems.
Northeast Regional Agricultural Engineering Service, Ithaca, NY.
Wood-Gush, D.G.M., I.J.H. Duncan, and C. J. Savory, 1978. Observations on the social behavior of domestic fowl in the
wild. Biol. Behav. 3:193–205.