Selection of Animals for Testing
To accurately represent the health status of the population, animals selected for health testing must mimic the population within the colony as well as be of sufficient age and exposure. Our standard operating procedure dictates documentation and training for Taconic Biosciences' animal selection practices. The age of any animal selected for health testing ranges from a minimum of 8 weeks through retired breeder (typically not more than 7-8 months of age). This time frame is consistent with FELASA recommendations. Colony staff selects animals from lines in the colony and/or sentinels, and over time this represents the entire animal population. Animals selected at each sampling time must be chosen from different colony areas or colony types (holding, active breeders, replacement breeders, etc.), racks, and cages to meet selection criteria. Colony staff record critical information (stock or strain name, date of birth, location in colony, etc.) for every animal selected for health testing and this information is also available for auditing purposes.
Use of Sentinels
Taconic utilizes sentinel animals to facilitate health monitoring of all colonies. The stock or strain utilized as sentinels is of key importance as the strain must readily seroconvert to viral agents. For mice, the preferred sentinel is the C3H (C3H/HeNTac). This strain not only efficiently seroconverts in response to viral agents; it is also available as gnotobiotic stock and has a unique coat color to minimize risk of genetic contamination. For rats, the preferred sentinel is the Sprague Dawley® (NTac:SD). This model is also available from gnotobiotic stock and delivers a robust serological response to viral agents.
In most situations, small breeding colonies of sentinel animals are maintained in the test location. In some instances, line animals are utilized as sentinels with veterinary approval. In either case, the sentinel animals are exposed to soiled bedding, feed and water from the other colony cages. Animals must be exposed for a minimum of 6 weeks prior to being selected for health testing. The exposure of sentinel animals to colony animals and their environment is of paramount importance. Generally there is at least one sentinel cage per rack of colony cages or one sentinel cage for every ~75-160 colony cages. Caretakers collect and transfer soiled bedding, feces, nesting material, etc. from colony cages into sentinel cages on the same rack. Sentinel animals also receive used feed and water from colony cages. To minimize the risk for genetic contamination, cohabitation of sentinel animals with colony animals is not practiced.
Sentinels are of particular importance in locations where immune-compromised (e.g. nude mice and rats, SCID mice, RAG2 knockout mice) or genetically modified animals are housed. These animals are either incapable of generating a serological response to viral agents or have an unknown response to viral antigen. In some instances, these animals are more susceptible to bacterial agents (for example Corynebacterium bovis). For these locations, line animals are utilized for the diagnostic portion of health monitoring (microbiology, molecular biology, and parasitology) and sentinels are used for the serological portion.
The introduction of dried blood spot testing allows Taconic to in some cases use sentinels for repeated testing, reducing the total number of sentinel animals required.