Note: Descriptions are shown in the official language in which they were submitted.
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Background o he Invention
The present invention relates to caging systems for
housing and isolating laboratory animals, and in particular to
cage assemblies for the breeding of colonies of mice, rats or
other small laboratory animals or for laboratory experimental
work with such animals. Each of the cage assemblies includes a
see-through cap or bonnet which has a detachable reusable
filter, and remains securely in place on the cage Cody without
being fastened whereto, to function as an effective microbiologic
eel barrier.
In the production of colonies of mice or other small
labora~vry animals by breeding, the mice are housed in animal
cages which are arranged in close proximity within confined
areas. The colonies are subject to air-borne diseases which
spread rapidly from one cage to another, particularly where the
surrounding environment is not particularly sanitary. It is
particularly desirable to maintain a closed, limited Defined
Flora colony that is a colony of mice having a limited number
of bacteria which are constantly the same. It has hitherto been
impossible to maintain a constant flora over long periods of time
without employing complex isolator systems which are expensive and
not economically feasible in the breeding production of laboratory
mice.
The same problems are encountered in the Montanans
of the animals during laboratory experimental work Although the
surrounding environment is more sanitary, the animals are
housed in open cages which are arranged in close proximity to each
other, usually on multi-tier racks. The animals in the different
cages may be infected with various selected diseases while others
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may be uninfected for comparison purposes. It has been difficult
or impossible to prevent the spread ox diseases from one cage to
another without employing complex isolator systems.
Conventional cages for small laboratory animals are
usually of the open-meeh type in which the cage side and bosom
walls are made of wire grill or perforated metal, or of the "shoe-
box" type having solid imperforate side and bottom walls made of
transparent plastic material, and an open top. The cage assembly
of the invention herein is directed to the latter type of "shoe-
lo box" transparent cage body, in combination with a jilter cover
thrower. The cage body may include a removable lid made of a
grid of straight spaced bars, and shaped to contain hoppers for
the storage of food and water which are easily accessible to the
animals within the cage. The term "cage", as used in this
description, generally refers to a cage body or tray having
solid side and bottom walls and an open top, with the optional
inclusion of a grid-type lid overlying the open top and having
means for molting water and food containers.
In the use of such cages for animal production or
experimental laboratory research, it is imperative that bacteria-
logical conditions established in an individual cage be main-
twined for as long as such conditions are desired. It is also
desirable to have a clear view of the animals through any top
cover provided for the cage since other potion of the cage are
occasionally obstructed.
Attempts to accomplish these objectives are well known
in the at. or example, US. Patent No. 3,343,520 discloses
a disposable animal cage filter cover having a body formed of
glass fibers and polyvinyl chloride. The filter cover is made
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Roy a blank that is cut into sexual panels, folded and assembled
or made prom a collapsible construction. Cut-outs are included in
the filter cover for transparent window members. Iris structure
is not autoclavable and its sterility at the time of use cannot
be assured. Furthermore, the cover can be easily dislodged
during use, thereby upsetting the microbiological conditions in
the cage. In addition, the recurring expense. associated with such
a strut lure as well as the establishment of a safe disposal
procedure for the covers after their use are further problem
that must be dealt with.
US. Patents Nos. 3,528,227, 3,528,390 and 3,613,639
show animal cage covers that are molded in one piece from a
fibrous web material, such that the entire cover constitutes a
filter. Although these covers can be reused, they are opaque,
light-weight and tend to dislodge on the cage, especially when
one cage is placed in close proximity to another where abutment
of adjacent cage covers is likely.
It is thus desirable to provide a reusable filter cap
or cover for an animal cage that has the microbiological integrity
of a complex isolator without high cost or awkward limitations
on thy movement of people and animals. It is also desirable
thaw such cap permit viewing of the encaged animals and be auto-
cleavable.
It is an object of the present invention to provide
an animal cage filter cap which is constructed to be removably
mounted in secure position upon standard animal cages having
solid transparent walls, and which provides with the cage an
effective microbiological barrier for the animals housed therein,
and minimizes the emission of animal odors from the cage by
maintaining limited defined anaerobic bacterial flora.
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A~lothex object of the invention is the pxoYision ox an
animal cage filter cap of the type desc~lbed which it reusable
and which mounts a removable and reusable filter! both the cap
body end jilter being capable of being autocla~ed.
Another object of the invention is to provide an animal
cage jilter cap of the character described which is transparent
so that the housed animals can be observed there through, and
which is rigid, durable, easy to handle, easy to sterilize, uses
minimal rack space, and does not dislodge when adjacently
lo disposed cages are pushed against one another during handling.
A further object of the invention is the provision of
an animal cage filter cap of the character described which is
incorporate in a novel cage assembly and caging system which is
- simple to use, inexpensive to produce, and allows easy access to
selected cages without time consuming entry procedures.
Summary of the Invention
In accordance with a preferred embodiment of the invention,
the animal cage cap is in the shape ox a box-like enclosure having
a transparent body portion sized to fit upon the open top end of
top animal cage in overlapping relationship with the cage wall.
The cap body portion has a resting surface which is formed to
engage a corresponding surface portion of the cage to effect a
substantial seal like a putter dish between the cap and the cage.
The cap body portion also includes a rigid flange which encompasses
the cage such that the cap cannot be dislodged from the cage, but
must be lifted off for removal. The cap body has an open top
portion covered by an overlying autoclavable filter which is
detachably secured to the cap body and is removable and reusable.
Additional objects and advantages ox the invention will
become apparent during the course of the following speci~icatlon
when taken in connection with the accompanying drawings, in
which:
S Brief Description of the Drawings
Fig. 1 is a perspective view of an Cumuli cage assembly
incorporating one embodiment ox the present invention;
Fig. 2 is a side view of the animal cage assembly of
Fig. l, with a portion thereof broken away and shown in section;
lo Fig. 3 is an exploded perspective view of the cap lid
of the assembly of Fig. l;
Fig. 4 is an enlarged Fragmentary sectional view of the
upper corner of the cage lid, as viewed ion Fig. 2, showing the
manner in which the filter is detachably secured to the cap
housing;
Fig. 5 is a sectional view waken along the line 5-5
of Fig. 2;
Fig. 6 is a top plan view of the cage lid or contain-
mint member;
Fig. 7 is a side elev~tional view thereof; and
Fig. 8 is an enlarged fragmentary plan view ox a
protective member for the filter, and appears with. Figs. 3 & 4.
Description of the Preferred Embodiments
Referring in detail to the drawings, a cage assembly
incorporating one embodiment of the invention is generally
referred Jo by the reference number lo in Fig. 1.
The cage assembly 10 comprises a box-like animal cage 12
with a cage lid or containment member 14 supported on a
peripheral lip 16 of the cage 12. The term "cage", as used here-
in, generally refers to the combination of the cage bottom 12 and
the cage continent member 14, although incorporation of the latter
ion the assembly 10 is optional. The cage assembly 10 also includes
a filter cap 18 which covers the cage 12 and the cage containment
member 14.
The cage 12 is formed with integral side walls 19 and a
bottom wall or floor 20 and an open top end. The walls are
preferably formed of a clear transparent plastic such as polyp
carbonate, which is rigid, durable, permits ready inspection of
animals, has a high impact strength, and is machine washable or
autoclavable at temperatures under 250~F. Such cage is
conventional, commercially available, and widely used. A
standard absorbent bedding of particulate material such as wood
chips (not shown may be spread on the floor 20 (Fig. 2) of the
cage 12. The open top of the cage 12 is bordered by the lip 16
which extends continuously there around. The cage 12 also
includes corner reinforcements 21 as most clearly shown in
Figs. 1 and 5.
The carp lid or containment member 14 shown in Figs. 6
and 7 is disclosed in US. Patent No. 3,358,649 which is Essex-
tidally a bar construction formed of stainless steel for example.
Top member 14 comprises an outer rim 22 which is disposed on the
lip 16 of the cage 12. A plurality of bars 24 extend across the
rim 22. The cage lid or containment member 14 is employed to
mount containers for food and water in a position in which they
are readily accessible to the animals within the cage. For this
purpose, some of the bars 24 are depressed and bent angularly
so
to Norm a water bottle compartment 26 with a bottle support 28
and a food compartment 30. The compartments 26 and 30 are divided
by a singable divider panel 32 and are bordered by end panels 34
and 36.
The filter cap 18 comprises a body portion 38 in the
general shape of a deep tray or box. I've body portion 38 is
preferably formed of clear plastic such a polycarbonate having
the properties previously descried for the cage bottom 12. The
body portion 38 includes respective opposed side walls 40, 40,
and end walls 42, 42, with corner reinforcements 44 at the
intersections of the side walls 40 and 42. Surface means on the
body portion 38 for resting the filter cap 18 on the cage 12
include a continuous peripheral flange extending perpendicular-
lye outwardly from the walls 40 and 42. Means on the body portion
38 for encompassing the cage 12 include a continuous peripheral
flange 48 depending from the peripheral flange 46 and having an
outwardly-extending rim portion 50.
As most clearly shown in Fig. 5 the flange 48 is spaced
from, encompasses and overhangs the lip 16 of the cage 12. Thus
I the filter cap body portion 38 cannot be dislodged from the cage
12 and must be lifted off to be removed. It should also be noted
that the clearance space between the flange 48 and the lip 16 permits
only a slight movement of the filter cap 18 on the wage 12. How-
ever, the peripheral flange 46 is of sufficient lateral extent
to remain in contact with the cage lip 16 or with its overlying
lid 14 despite any relative lateral movement between the filter
cap 18 and the cage 12, to maintain the integrity of the seal
between the filter cap and the cage.
The filter cap body portion 38 has a top open end
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b~dered by a neurology 52 which extends continuously around
the cap body portion 38, as shown in Figs. 3 and 4. Cross arms 54
and 56 aye muddied integrally with the ledge 52 and intersect with
a central annular portion 58, as shown in jig. 3. The ledge 52,
cross arm 54 and 56, and annular portion 58 are co-planar, and
are recessed a short distance below the top edges of the filter
cap side and end walls 40, 42. Enlarged triangular portions 62
are provided at each intersection ox the ledge 52 with the cross
arms 54, 56. The enlarged portions 62 are provided with
fastener openings 64.
The ledge 52, cross arms 54, 56 and central annular
portion 58 are provided as means for detachably securing an
air filter 60 in a position in which it overlies the top open
end of the filter cap body portion 38, and for supporting said
filter 60 immovably in mounted position.
The filter I is a thin sheet of spun-bonded polyester
of the type sold by Du Pont under the Trademark ~EEMAY 20-24.
A filter thickness of between 11 and 13 mill has been found-
adequate for a filter having an area approximately equivalent to
top area of the cage floor 20.
The filter 60, in mounted position, extends across the
opposite ledge portions 52 and is supported at its edges
thereby, the central portion of the filter being supported by
the cross arms 54 and 56 and thy annular portion 58. A protective
plate member 66, preferably formed of aluminum and provided with
a plurality of perforations 68, is disposed over the filter 60 in
flush abutment therewith. The plate member 66 may haze a thick-
news of l/16", with l/8" perforations on 3/16" center lines. The
filter 60 and plate member 66 are removably secured to each
so
other and to the filter cap body portion 38 by a plurality of
fasteners preferably in the fox of treaded bolts 70 which pass
through holes 72 in the filter 60 and aligned holes I in the
plate member 66, the holes 72 and 74 registering with the
S fastener openings 64. The fastener bolts 70 are preferably
formed of stainless steel and are engaged by respective nuts 76,
also formed of stainless steel. During use of the filter zap lo
these fasteners provide means for disassembling and removing the
filter 60 and plate member 66 for individual cleaning, sterilize-
lo lion, or replacement.
In the assembled filter cap lo, the perforated plate 66
overlies the filter 60 in flush abutment therewith, to protect
the filter against damage during handling and prevent its
buckling, while the filter 60 rests flush upon the ledge 52 and
cross arms 54, 56 which support it in muted position. The ledge
52 and cross arms 54, 56 are recessed at such a distance below
the top edge of the filter cap body portion 38 that the upper
surface of the mounted perforated plate 66 is on a plane
substantially flush with said top edge or is slightly recessed
thereb~aeath, as shown in Fig. 4.
In a commercial embodiment of the invention, the filter
cap 18 is sized to fit upon a conventional transparent
polycarbonate animal cage having a depth of approximately five
inches, a top open end of approximately if 1/8 inches in length
and 6 7/8 inches in width. The body portion of filter cap 18
has a height of four inches, a top open end lo ll2 inches in
length and 5 3/4 inches in width, and a bottom open end (between
the inner surfaces of peripheral flange 48) of if 13/16 inches
length and 7 l/2 inches width. The filter 60 measures ten inches
in length and 5 5/8 inches it width, and the plate 66 is of
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slightly sm~llex dimension. The assembled latex cap 18 weighs
fourteen ounces.
In use of the cage assembly lo, the floor of the cage 12
is covered with bedding material (no shown and one or more
animals such as mice are placed thereon. The lid or containment
member 14, if desired, is then positioned on the cage lip 16 and
food and water are provided in the respective compartments 26
and 30. The filter cap 18 is then positioned on the cage 12 in the
manner shown in Figs. 1 and 2, and remains securely in place
until lifted off. In the mounted position of the filter cap 18,
its lateral peripheral flange 46 rests upon the outer rim 22 of
the containment member 14, which in turn us resting upon the lip
16, as shown in Fig. 5, to provide with the overhanging flange 48
an effective air seal for the interior of the cage assembly.
If the lid 14 is not included in the cage assembly, the flange
46 would rest directly upon the lips 16 to provide the same air
seal. Because of its dimensions, and because of its relatively
heavy weight, the filter cap 18 rests flush and firmly on top of
cage 12 providing a seal around the edges, and cannot be easily
dislodged. When it is necessary to remove the jilter cap 18 for
feeding or treatment of the animals, the filter cap may be simply
placed on a towel soaked in disinfectant to maintain the
cleanliness of the rim portion 50.
The caging assembly 10 is sized to facilitate monopoly-
lion of the filter cap 18 with one hand. The protective plot permits rough handling of the filter cap 18 without causing
damage to the filter 60, and the entire filter cap can be
autoclave as a unit for continual reuse. Since the flange 48
closely envelopes the open top of cage 12, there is minimal loss
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of rack space when cages are in close prompt to each other
and the abutting of one jilter cap 18 against another jilter cap
is unlikely to dislodge the filter caps from their respective
cages.
Since the filter cap 18 overlaps and encloses the cage
12 and fits snugly thereorl, a giant petri-dish like structure is
obtained. The overlapping filter cap effectively keeps dust
particles, which are the microbiological taxis, out of the cage
assembly. Accordingly the assembly 10 is essentially a miniature
isolator, a protected microenvironment within any macro environ-
mint. The filter 60 while functioning as an effective
microbiological barrier, permits a substantial interchange of
gases there through, so that the animals receive a substantial
supply of fresh air. Thus, the disclosed caging assembly
effectively isolates small laboratory animals from their outside
environments which may include airborne contaminants such as
viruses, bacteria or any particulate matter. The cage assembly
also prevents cross-contamination between cages by aiding in
infection confinement. Thus the caging system is also a first-
rate quarantine housing system because animals from different sources with differing microbiological profiles can be
quarantined in the same room without cross-contamination. the
barrier works in both directions. It can keep contaminants in or
Owlet. Thus, the cage assembly disclosed herein has the
microbiological integrity of a complex isolator.
It has been found that cage assemblies as disclosed
herein permit the maintenance of a limited stable flora, allow
freedom of movement of animals within a colony and with
minimal emission of odors. It has also been found that the
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ammonia level within the colony it not a problem it the population
density per cage is kept at 3 to 4-mice, end bedding changed every
3 to 4 days, especially when relative humidity cannot be controlled.
Ammonia can be totally eliminated from the colony if defined flora
mice without urease~positive aerobic bacteria are used. also by
using a small amount of bedding which is stirred by the animals,
the cage can be kept reasonably dry between changes.
While a preferred embodiment of the invention has been
shown and described herein, it is obvious that numerous additions,
changes and omissions may be made in said embodiment without
lo departing from the spirit and scope of the invention.
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