Mouse Breeding Systems

1. Mouse Breeding Systems • General Mouse Information • Factors That Influence Breeding • Breeding Systems • Record Keeping

2. General Mouse Information • Average lifespan is 2 years • Breeding life is 8 months • Reach sexual maturity at 28-42 days of age • Breeding onset: Females 6-8 weeks Males 8-10 weeks • Gestation is 19-21 days • Litter size 2-16 pups per litter • Breeding retirement: After having 5-6 litters or 6-8 months of age

3. Strain Age Health Technician Temperature Humidity Lighting Diet Water Nesting Material Number of mice Age Bred Disturbances Factors That Influence Breeding Production

4. Inbreeding • Homozygous animals • Inbred strains are desirable due to their high degree of homogeneity • A strain is considered to be inbred after 20 consecutive generations of brother/sister matings

5. Line Breeding • Homozygous animals • More intensive form of inbreeding • Animals must have common ancestor in order to be bred to each other

6. Outbreeding • Heterozygous animals • Desirable due to their high degree of individual diversity • Maintained by random matings. Usually a planned breeding scheme that ensures that only unrelated animals are bred • Usually have bigger litters with stronger, larger pups than litters of inbred strains

7. Breeding Systems • Monogamous • Polygamous • Timed • Observed

8. Pros: Ease of accurate record keeping Uses postpartum estrus Parents are known Don’t have to separate mice Little male burnout Exact date of birth for each litter Maximum number of litters per female during her life span Monogamous:One male continuously bred to one female.

9. Monogamous:One male continuously bred to one female • Cons: • Higher number of males required • Higher number of cages • If one of the breeders in an inbred strain dies it can be difficult, if not impossible to replace • If the male is aggressive he may cannibalize pups and possibly injure the female

10. Pros: Requires fewer males Fewer number of cages needed Can reduce exposure of pups and females to male aggression Good way to get large number of litters quickly Polygamous, AKA Harem Breeding:One male bred to multiple females

11. Polygamous, AKA Harem Breeding:One male bred to multiple females. Cons: • Higher level of technician responsibility • Fewer litters per female • Higher male burnout than monogamous breeding • Can be labor intensive • Accurate record keeping more difficult • May not be sure who the mother is • More than one litter can be born in a pan • May loose postpartum estrus breeding

12. Trios • Often left together • Co-parenting • Can mix females • Can help conception rates • Watch for overcrowding • Can be hard to determine maternal lineage of pups

13. Timed Matings • Mice are bred for a specified period • Predictable litter due date • Stage of pregnancy • Gestational age of pups • Does not require checking for plugs • Less labor intensive than observed mating

14. Observed Matings • Female is bred to male. The next day begin checking for vaginal plugs • Females are separated from the male once a plug is found • Predictable litter due date • Plug is not a guarantee of pregnancy • Requires handling of mice

15. DOCUMENTATION • DOB • Lineage • Identification • Strain • Sex • Dates bred • Weaning information • Initials