In laboratory animal husbandry, there is a huge demand for animals that have been kept in disease free conditions and housed in barrier units such as Individually Ventilated Cages (IVCs). This is very important because when animals are used for scientific research, particularly drug related research, the animals must provide accurate and valid results. If the animals are suffering from any disease that could potentially affect the results that have been obtained from the experiment, the results should not be used. Every experiment using animals will have severity limits which, legally, must be adhered to. Using a sick animal may cause the severity limit to be exceeded. If the animal already has a disease and then undergoes experimentation of a substance that also produces effects on the animals health, it could potentially worsen the effects of the agent being tested causing the animal to experience more suffering than necessary. The animals may produce false results which may prove vital at a later stage, e.g., in drug trials on humans. Not only that, the experiment will have to be performed again and the previous animals would have been wasted. This is why it is important to ensure that the animals are clean. To protect animals from any disease-causing pathogen (such as bacteria and viruses), a high quality caging system should be carefully chosen to suit the specific requirements of the user. IVC's should be able to prevent large fluctuations in climate controls ensuring all environmental conditions (such as humidity and temperature) are kept at a relatively constant level and within the correct range suited to the animal housed inside (ranges can be found in the Home Office Code of Practice). High or low environmentals can cause stress to the animal and seriously affect their health. Specially hygienic states that are called Specific Pathogen Free (SPF), are potentially very vulnerable to every outside influence. This is because they have never been exposed to micro-organisms before. Special caging systems are often used alongside many other barriers to keep unwanted materials out of range of the animals.
The IVC-systems in which the animals are kept in ensures they are fully protected by use of HEPA-filters (High Efficiency-Particulate Air) that defends them from all micro-organisms. A process of sterilisation of all items to be passed in to the barrier unit including bedding material, food etc. must be performed, especially the cages made out of special synthetic polycarbonates. Although the physical resistance of the material which the cages are made from allow various methods of sterilising and disinfecting to be carried out, routine sterilisation can cause discolouration and brittleness after time.
The cages are constructed and designed in a specific way to ensure an absolute microparticle free inner environment. This generally includes a cage bottom, a cage top (with a food hopper and water bottle holder incorporated) and a filter lid. It is also designed to allow maximum comfort of the animal and to provide a secure, chew proof environment. An external ventilation unit supplies the cages with fresh HEPA-filtered air which passes through the filter lids. The ventilation-system mostly consists of two tubes for ingoing and outgoing air.