Animal Welfare Information Center Newsletter, Fall 1994, Vol. 5, no. 3
by
A.J. Anzaldo, University of Illinois, Urbana-Champaign (UIUC),
P.C. Harrison, UIUC, G.L. Riskowski, UIUC, L.A. Sebek, UIUC,
R-G. Maghirang, UIUC, W.R. Stricklin, University of Maryland, College Park, MD,
and H.W. Gonyou, Prairie Swine Center, Inc., Saskatoon, Saskatchewan
The general public is increasingly becoming concerned with the
welfare of animals used in research. This concern is well
justified in an era of booming technology and of using animals to
help solve unanswered questions. A major concern of many people
is the housing and living conditions laboratory animals must
endure while undergoing experimentation, including space allowed
for each animal when housed in a group. As researchers,
concerned and appreciative of our animals' needs, we continue to
search for what is "best" or "optimal" for their living space.
Dawkins (1980) argued that the animals' perception of their
environment or subjective experience is the essential component
of welfare. Dawkins also (1990) supported the idea of using
preference tests to "ask the animals" which environment is best
for them. We were able to take Dawkins' ideas and do just that,
ask the laboratory rats where they preferred to live. Remarkably,
we found that "bigger is not always better." Improving the design
of caging may be a means of achieving high-density housing of
laboratory rats while obtaining the level of welfare the Public
Health Service (PHS)-National Institutes of Health (NIH)
guidelines are intended to ensure. Thus, it could be possible to
house rats in less area, when needed in certain circumstances,
provided the living space is of better quality. For example,
physical space available to house animals in the National
Aeronautics and Space Administration space station research
modules will often be limited, and adherence to PHS guidelines
for floor space would severely limit the animal research program.
However, taking into account behavioral as well as physiological
needs of laboratory rats, two alternative cages were designed and
tested.
To: Top of Document | Introduction | Cage Design | Methods | Results and Discussion | References
Cage Design
The two cage designs selected were the high perimeter (HP)
spatially enhanced cage (SpEC) and the 3-D (3-D) SpEC. The inside
dimensions of both SpEC's were 305 mm wide, 432 mm long, and 330
mm high; the distance from floor to wire top was 203 mm (figure 1).
Based on the 1985 NIH Guide to the Care and Use of
Laboratory Animals, each cage can house six 300 gram rats or
three 600 gram rats. The two cage designs are discussed below.
Rats and some other animals, such as cattle (Stricklin et al.,
1979), guinea pigs (White et al., 1989), and pigs (Weigand and
Gonyou, unpublished data), are thigmotactic (edge-users). These
animals tend to "shy away" from the center of barren cages.
Instead they prefer to spend most of their time in contact with
surrounding walls of the cage, seldom using the floor space
available in the center. Chamove (1989) found that weight gain in
mice could be increased by adding vertical cage dividers and
increasing the wall surface area available for contact. Thus,
with the support of this growth data, we designed a cage in an
attempt to better use the total space of the cage. This HP-SpEC
was equipped with a set of L-shaped partitions for tactile
retreat and additional wall contact (figure 2). The partitions were placed so that a 76 mm wide space was available between the
interior partitions and the outer wall of the cage.
Using the entire volume of the cage may be another means to
compensate for decreased floor space in the laboratory. This
concept has been demonstrated in poultry houses where birds are
free to move among perches and platforms as a means of increasing
their welfare (Tauson, 1991). Again, Chamove's (1989) most
successful treatment for mice involved a second deck within the
cage. Thus, a second cage which allowed the rats to move in three
dimensions, to better use the volume of the cage, was constructed
(figure 3). The 3-D SpEC included two platforms mounted on the exterior walls of the cage. These platforms ran the length of the
cage with the exception of 76 mm on either end. Two interior
walls provided support for the platforms and also additional wall
contact. These extended from the bottom to the top of the cage
and the length of the cage, with the exception of 76 mm on either
end to allow access to the shelf areas. This setup almost doubled
the amount of floor space available to the animals.
To: Introduction | Cage Design | Methods | Results and Discussion | References
Methods
The two SpEC designs were compared in a series of preference
tests to determine the type most readily accepted by mature male
rats (Sprague-Dawley, 500 gm). The preferred SpEC was then
tested against a standard cage (STD) (figure 4)
meeting NIH requirements for six (500 gm) rats. Each phase of the preference
testing (HP-SpEC vs. 3-D-SpEC and SpEC vs. STD) was divided into
two stages. One stage tested a group of 6 rats and the other
tested a group of 12 rats to observe possible differences in
behaviors due to increased density. Each stage was replicated
eight times. All preference tests involved simultaneous access
to two cage types. Rats were able to move between the two types
of cages by an open passageway.
Rats were tested over a period of 6 days according to the
following schedule.
- Day 1 --- SpEC cage acclimation (24 hours)
- Day 2 --- SpEC cage acclimation (24 hours)
- Day 3 --- returned to polycarbonate cage (24 hours)
- Day 4-6 - preference testing (72 hours)
Observations were taken via videotape, and seven mutually
exclusive behaviors were recorded which included: 1) recumbent,
2) social interaction, 3) licking, 4) stretching, 5) eating, 6)
drinking, and 7) active.
To: Introduction | Cage Design | Methods | Results and Discussion | References
Results and Discussion
Over a 24-hour period, the six rats spent significantly more time
in the HP cage as compared to the 3-D cage, 80.2 percent vs. 19.8
percent, respectively. This observation continued with the
addition of 6 more rats with the group of 12 rats spending
significantly more time in the HP than in the 3-D, 80.5 percent
vs 19.5 percent, respectively. There are several explanations for
the greater use of the HP, especially the center of the cage,
over the 3-D cage by the rats. First, because rats are
thigmotactic and very social animals, they prefer to huddle and
sleep together when housed in groups. The design of the HP
allowed the rats to maintain contact with the L-shaped wire mesh
walls as well as maintain contact with other members of the
group. The 3-D cage may have limited the space for the rats to
gather as a group as well as perform certain behaviors such as
grooming. The space available outside the L-shaped perimeter
allowed the rats to continue to eat, groom, and interact, if they
chose to leave the center where the rest of the group slept.
The true preference test lied in the comparison of the HP vs STD
cage. The rats continued to choose the HP at a significantly
higher rate. The percentage of time observed in the HP for 6 rats
was 79.6 percent vs. 20.4 percent for the STD. Similarly, the
12-rat group chose the HP over the STD, 66 percent vs. 34 percent
of the time. The increased activity (amount of time spent
performing observed behaviors) in the 12-rat STD cage may be
attributed to the rise in active behaviors during darkness. The
rats may have found it easier to eat, drink, interact socially,
and, in general, remain active in the STD cage rather than "wait
in line" to accomplish these behaviors in the HP. It was still
apparent, especially when the rats were recumbent or resting,
that they overwhelmingly chose to reside in the HP. However, the
reduction in occupancy of the HP from 79.6 percent to 66 percent
suggests that the increase in density from 6 to 12 rats is
reaching the maximum limits of the HP cage. Further study is
warranted.
The rats chose social interaction and security over extra floor
space, thereby defining what their needs really are when it comes
to space. In the midst of the revision of the PHS Guide to
the Care and Use of Laboratory Animals, it is imperative
that researchers attempt to quantify what animals inherently
need. It should not be merely a guess at numbers. However, we
should continue to strive to improve their way of living, as they
have continuously done for us.
This research was supported by the National Aeronautics and
Space Administration.
To: Introduction | Cage Design | Methods | Results and Discussion | References
References
Chamove, A.S. (1989). Cage design reduces emotionality in mice.
Laboratory Animals 23:215-219.
Dawkins, M.S. (1980). Animal Suffering: The Science of
Animal Welfare. Chapman and Hall, London.
Dawkins, M.S. 1990. From an animal's point of view: Motivation,
fitness and minimal welfare. Behavioural and Brain
Science 13: 1-61.
Maghirang, R.G. and G.L. Riskowski (1994). Spatially enhanced
caging for laboratory rats at high density. Accepted: ASHRAE
Transactions.
Stricklin, W.R., H.B. Graves, and L.L. Wilson (1979). Some
theoretical and observed relationships of fixed and portable
spacing behavior of animals. Applied Animal Ethology
201-214.
Tauson, R. (1991). Research approaches to improve the technical
welfare and the environment of laying hens. In International
Conference on Farm Animal Welfare: Ethical Scientific and
Technological Perspectives, Univ. of Maryland, pp.37-40
Weigand, R.M., H.W. Gonyou, and S.E. Curtis (1992). Pen shape
and size: Effect on pig behavior and performance. Unpublished
data.
White, W.J. (1989). Use of cage space by guinea pigs.
Laboratory Animals 23: 208-214.
This article appeared in the Animal Welfare Information Center
Newsletter, Volume 5, Number 3, Fall 1994
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