University of Oslo
Institute of Basic Medical Sciences, Section of Comparative Medicine Standard operation procedure: Breeding and maintenance of mice and rat lines SOP nbr: 3-03
Created: 20.07.2021 Created by: Frøydis Kilmer
Revised: Revised by:
Valid to: 05.08.2023 Approved by: Espen Engh
BREEDING AND MAINTENANCE OF MICE AND RAT LINES
1.0 PURPOSE
1.1 To ensure good breeding and maintenance of mice and rat lines at Section for Comparative Medicine (KPM).
1.2 To ensure that healthy animals are used for breeding and that healthy animals are produced (unless instructions to the contrary are given in FOTS).
1.3 To ensure that KPM is provided with important information regarding phenotypes.
1.4 To ensure that KPM is provided with important information regarding the type of experiment to be carried out.
1.5 To ensure that different lines of mice and rats are cryopreserved.
1.6 To ensure that the lines are backcrossed to prevent genetic drift.
2.0 DISTRIBUTION OF RESPONSIBILITY
2.1 The users are responsible for maintaining their mouse and rat lines.
2.2 The users are responsible for making sure that the breeding follows the description in FOTS.
2.3 The users are responsible for communicating important information about the line to KPM.
2.4 KPM organises the breeding in response to a request from the user and makes sure that healthy animals are used for breeding.
2.5 KPM informs the user if deviations occur.
3.0 PROCEDURE
3.1 The user is responsible for maintaining his/her own mouse and rat lines. KPM can give advice on breeding at the request of the user.
3.2 The breeding of mice and rats is usually carried out in the MDU. The breeding of mouse lines with special needs regarding hygiene status and type of experiment can be carried out in DU-044 and in the Barrier, subject to prior agreement with KPM.
3.3 The production of inbred animals may take place within the group as long as backcrossing has been carried out in accordance with current rules.
3.4 Animals for breeding in outbred lines should primarily be purchased from a vendor.
Institutt for medisinske basalfag, Avdeling for komparativ medisin 2
Breeding
3.5 The minimum production of a line should consist of two breeding cages, preferably with some overlap in age. Two back-up cages per gender should be maintained and the back-up animals should be changed by the time they reach the age of 7 months. Back-up animals in the Barrier must be labelled with “Back-up” in the “Notes” section about the animals.
3.6 The user sets up a “Breeding request” in Science Linker (SL). The name of the breed must be an approved abbreviation of the name of the strain, which corresponds to the name of the animals (for example, «NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ» can be abbreviated to «NSG»). Select ”Tag” + ”Take sample” if the offspring must be genotyped. Select “Tag” if the genotype is given, but ear tagging is required. Any important supplementary information, such as special phenotypes or e.g. whether the offspring are to have a running wheel or not, should be entered under “Description” in the request.
3.7 For mice, breeding can be set up as duo (a male and a female) or as trio (a male and two females), while duo is the breeding norm for rats (trio breeding is accepted in exceptional circumstances). Trio breeding with mice must be set up in GM900 cages, while GR1800 cages must be used for the breeding of rats. Trio breeding can result in more offspring than duo breeding.
3.8 The user must inform KPM if new lines are set up and all the offspring are to be preserved until the line is established. KPM routinely terminates single males/females in a litter (see SOP 5-03 “Weaning of pups in mouse and rat breeding”).
3.9 KPM sets up the breeding and ensures that the animals are healthy and without defects. KPM informs the user in the case of any deviations. The animals are checked carefully to make sure that they have the correct ear tagging (if applicable). KPM enters important information under “Notes” on the breeding cage.
3.10 A sufficient, but not excessive number of breeding cages must be prepared according to the number of animals needed for the experiment, plus back-up animals. The three Rs must be observed.
3.11 Young animals should be used for breeding, the ideal age being between six and twelve weeks.
However, older animals can also be used.
3.12 Give the male time to establish a territory if he is to be mated with females who are somewhat older.
3.13 The gestation period of mice is ca. 18-21 days, depending on the strain and the size of the litter. The gestation period of rats is ca. 20-23 days, depending on the strain and the size of the litter.
3.14 It is not unusual for the first mouse litter not to survive. Replace any breeding animals that have not produced a viable litter within approx. 60 days.
3.15 Change the breeding cage when the breeding animals are seven-eight months old in order to maximise production. The animals can produce young until they are about one year old, but production will decline and will put more strain on the female. The user can generate a “Termination request” for the animals if they are to be euthanized. If breeding is to cease, but the animals are not to be terminated, an “Other request” should be generated with a comment in the “Description” section.
3.16 Breeding with a plug check can be ordered via SL: generate a request for “Breeding” and “Plug check”
for the females in question. This type of breeding must be prepared during the week before the breeding is to take place.
Separation/weaning of litters
Institutt for medisinske basalfag, Avdeling for komparativ medisin 3
3.17 Litters of mice must be separated/weaned when they are 20 days old, while rat litters are separated/weaned on day 21. The pups must be given plenty of paper, a tunnel/igloo and wet food when they are separated, in addition to regular food, water and bedding. The animals must never be housed alone in a cage at such a young age. If some of the males/females in a litter are to be preserved, all the pups in the litter can be separated/weaned together and housed in the same cage until they are five weeks old. Male mice must then either be used in experiments or for breeding, or they are terminated. Females can be housed with other females of the same strain. Male rats can be housed with other males of the same strain. Ear tag the animals that are housed together so that they can be separated from one another.
3.18 Genotyping of the first litters, in cases where all the pups are expected to have a given genotype, is recommended in order to confirm that the breeding is correctly set up.
3.19 If pups are to be used in experiments, never remove all the pups from the mother in one go. At least two pups (of the same gender, if these are to be preserved after the separation/weaning date) must remain in the cage. Separate the litter in SL by selecting «Males remaining in breeding cage»/«Females remaining in breeding cage» and choose the correct category of termination in SL for the pups used.
Cryopreservation and backcrossing
3.20 All unique lines should be cryopreserved (the freezing of sperm/embryos at a very low temperature) - a service provided by the Norwegian Transgenic Centre at the Institute of Basic Medical Sciences (IMB), and by other national and global institutions.
3.21 The line must be backcrossed, in order to prevent genetic drift, with the original genetic background.
The backcrossing should take place after five generations and no later than after ten generations.
3.22 Lines must be named in compliance with current rules. See «MGI-Mouse Nomenclature Home Page (jax.org)” for more information on the nomenclature of mouse lines.
4.0 HISTORY OF EDITING
4.1 Written 15.07.2021 by Frøydis Kilmer
5.0 REFERENCES
5.1 General Husbandry Tips - JAX
5.2 Nomenclature for Mouse Strains - JAX 5.3 Cox-Genetic Bkg Effects.pdf
