Core breeding at the Wallenberg laboratory

Here, breedings using a small number of cages can be maintained for long periods of time. When needed, the offspring can be transported to other KM facilities to be used in experiments, or further transported to facilities outside of KM.

The  implementation of different barrier levels at KI is in place to create better conditions for animal research. That includes the possibility to move animals between different units without violating the health status of the different areas. The core breeding barrier (Barrier B2) at the KM Wallenberg Facility (KM-W) maintains the highest standard at KM for non-germ free rodents.

Maintaining the core breeding barrier

Several processes safeguard the health status of the Core breeding barrier, including:

• Only access to trained animal technicians
• Wet shower quarantine requirement for animal technicians
• Barrier infrastructure (air shower, autoclaves, gas locks)
• Handling mice with sterile forceps in laminar air flow benches
• Use of additional PPE for animal technicians
• Only accepting mice via re-derivation or from accredited vendors (see below)

Accredited vendors for the core breeding barrier

Due to the high health status of the Core breeding barrier at KM-W, the following requirements apply for purchasing animals from accredited breeders:

• Only animals from Charles River (Italy or France sites) or Janvier (France) are accepted
• Animals must have Specific Opportunist Pathogen Free (SOPF) health status
• Animals must be transported via car (transport via airplane is not permitted)

To minimise the risk of infecting the colony in the B-barrier, animals that arrive from accredited vendors are sampled and placed in a brief quarantine (estimated 2-3 weeks) before they can be introduced to the B-barrier. Please keep this in mind when planning your breeding in the B-barrier.

Purpose of core breeding

Maintaining live mice free from infections and genetically unchanged is the major purpose for keeping these animals in a protected and enclosed environment. This can be achieved by keeping a small set-up of breeding pairs for a specific strain in an area that is separate from all other barriers with limited access of personnel. In this way the core breeding unit serves as a live back-up repository for the most valuable and regularly used mice.

The core breeding is used as the basis (foundation stock colony) for each strain and is therefore a basic principle for producing animals for the expansion and production (research) colonies. It is not allowed to place mice inside the barrier without prior re-derivation. Even access of researchers is prohibited regarding the B-barrier.

Core breeding strategy

Both the core breeding and the expansion breeding are based on a strict inbreeding schedule (brother sister mating). The size of a core breeding nucleus should be around 10 to 50 breeding pairs, whereas 10 to 15 breeding pairs are normally sufficient (depending on the breeding performance of the strain). The core breeding pairs should be refreshed every 6 months, to avoid a decrease of the breeding performance.

The thorough genetic control and the refreshing of the gene pool of the strains are major prerequisites to maintain the strains in the core breeding unchanged. A genetic drift can result in the loss of the genetic modification, a changed phenotype due to mutations or loss of the initial phenotype.