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Training Introduction

What makes THOREN Caging so unique as compared to other housing systems?

THOREN Caging Systems, Inc. pioneered the development of warm surface plastic cages for rodents in 1953 and the Maxi-Miser® Positive Individually Ventilated System (PIV) in 1978 in conjunction with The Jackson Laboratory. Currently, Thoren offers a wide variety of rack options and cage configurations. Modular in design, the Maxi-Miser® PIV System can be constructed as a fixed or mobile unit using 12 basic cage designs. Racks accommodate a variety of rodent cage sizes, even on the same rack, meeting a variety of application needs. All units are available with bottle watering, automatic watering systems or a combination of both.

NEW Sampling at Rack Level

The PIV can be operated either from a central ventilating system or individually through Thoren's Blower/Filter Module, a self-contained unit that uses 99.99% efficient HEPA filters for both supply and exhaust fans. Sterile air for individual cages is supplied through a filter lid. Air is exhausted through the filter top and into the “in-shelf” exhaust channel. Racks may be air-balanced to be either positive or negative relative to the room, each being equipped with separate Magnehelic® Gauges to monitor supply and exhaust static air pressure. The entire system is autoclavable; even the Blower/Filter Module comes with detachable electronics to facilitate washing or autoclaving.

The Thoren PIV is a complete lab animal housing unit – an excellent complement to your Animal Care and Use Program.

Procedure Guidance for Thoren Racks

with Individually Ventilated Microisolation Cages


Cage-to-Cage Transfer of Rodents

Procedures for changing rodents maintained in IVC vary with the need for protection of the cage contents. Since the cage, itself, provides the containment environment, a break can occur whenever the cage is opened. Successful husbandry depends on the quality of the cage, hopper and lid, as well as the food, water, bedding, any enrichment, and the changing procedure itself. Successful transfer of rodents from soiled to clean cages requires attention to all aspects.

A. Conventional husbandry.

Although this may not be preferred, individual Institution standards prevail.

Cages with food and bedding are brought to the change site on flatbed carts, dollies, racks with individually assembled units or in stacks of components. Bottles with water (tap or RO) that may be acidified and/or UV-irradiated, are also made available. Various garb and PPE (possibly gown, bonnet, mask and gloves) may be required. Facility supply air may be HEPA-filtered.

Transfer of animals from soiled to clean cages may be done on a cart, table or other work surface. The work surface is properly disinfected. A soiled cage is removed from the rack, placed on the work surface and the lid, hopper and bottle removed from the soiled cage, exposing the animals within. The lid and bottle may be removed and hopper alone held in the non-dominant hand while the animals are transferred one at a time into the fresh cage, using the dominant hand and forceps kept in disinfectant when not in use. Then,


a) a fresh hopper, water bottle and lid are placed on the clean cage; or,


b) the hopper and lid from the soiled cage are transferred to the clean cage and a fresh water bottle is supplied; or,


c) a fresh hopper is placed on the clean cage with fresh water bottle and the lid (only) from the soiled cage is placed on the clean cage.


This continues for the number of cages to be changed. Transfer of animals from a cage without a hopper may present opportunity for escape. This must be avoided. Finally, care must be taken to transfer the cage card from the soiled cage to the fresh one, guaranteeing the correct card is transferred. Emphasis is on the rapid transfer of rodents from the soiled cage to the clean cage. Given these procedures, it may be possible to change cages at a rate of 60 or more in an hour.

B. Barrier husbandry.

This set of procedures requires the Thoren Change Station (CS). Used correctly it will provide Product Protection. To maintain the sterile, protective environment, the cage must only be opened within the operating CS. Gloved hands are kept wetted with a suitable sterilant, ensuring that all contact with the animals, cage interior, transfer forceps, food, water bottles and cage lid is done only with wetted, gloved hands. If the lid and hopper are to be reused, they should be placed on a sterilant-wetted pad while not on the cage. It is best if the lid is not inverted, but rather placed on the change station work surface in its normal orientation. If a supplemental food container is kept in the CS to “top-off” hoppers, care must be taken to refill it within the sterile CS with sterilized food. Water bottles need to be sprayed with sterilant or wiped with a sterilant-wetted cloth or towel before being placed in the fresh cage. Attention needs to be paid to all steps of cage, bottle and animal handling to maintain the sterility of all materials that contact the animal. Periodic review of procedures will help assure they are appropriate.


C. Containment husbandry.

A properly used Biological Safety Cabinet (BSC) is required to provide both Product and Personnel Protection in rodent husbandry. While the cage change procedures are similar to those for Conventional and Barrier husbandry, the need for absolute containment within the IVC requires careful attention to all details of containment within the LAF envelope of the BSC while the cage is open.



To accomplish strict pathogen-free husbandry in micro-isolation cages, all components for husbandry must maintain the sterile environment. With bulk bedding dispensing systems in cage prep areas, cages are assembled with bedding, hopper and lid, placed on racks and autoclave-sterilized. If autoclavable diet is used, it is added to the hopper at assembly before autoclaving the fully assembled cages. Sterile cages are transported on racks to place for cage change. Water bottles are normally prepped separately, either sterilized empty and sterile water dispensed individually in a sterile (LAF) environment or filled with water and placed in bottle baskets which are then wrapped (or double-wrapped) and autoclaved then set in the BSC at cage change for placement in individual cages. Finally, there is nothing curative about maintenance of rodents in the IVC. That being said, self-limiting infections may resolve over a period of husbandry, depending on the agent in question. This, however, is not usual and should not be presumed.


Special note:

Each time an animal is transferred is an excellent time to give a brief examination for health concerns. Also, the cage contents should be checked with the cage card for number and gender of the animals contained. Any discrepancy should be noted and brought to the attention of the appropriate individual according to Standard Operating Procedures.



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