New to Lab Mouse Experiments? Learn Lifecycle & Best Ages for Your Research

Introduction

Embarking on an animal experiment, especially when you're not well - versed in lab mice, can seem daunting. But don't worry! Understanding the life cycle and ideal ages for experiments is key. Let's dive in.

The Life Cycle of Laboratory Mice

Laboratory mice are crucial in drug discovery and disease research, despite their short lifespan compared to humans.

Embryonic Stage

After the zygote forms in the oviduct ampulla, it transforms into a morula in about 3 days. By 5 days, it becomes a blastocyst, starting the implantation process. The gestation period lasts 19 - 21 days.

Postnatal Early Life and Lactation

Day 0: Newborn pups are hairless, with pink skin, and their eyes are tightly shut.
Day 3: The umbilical cord detaches, and ear pinnae start to show.
Day 7: Fine hair covers their body, and the toes are fully separated.
Days 12 - 14: Their eyes fully open, and they begin to eat solid food.

Weaning Period

Pups are weaned at 3 weeks old and start their independent life. At this stage, male and female pups must be separated. As they adapt to the new environment, they gradually display adult - like behavioral traits.

Early Juvenile and Growth Period

Females reach vaginal opening patency at around 4 weeks.
Males experience testes descent into the scrotum by around 5 weeks.

Late Juvenile Period

This occurs 5 - 8 weeks after birth.

Sexual Maturity Period

Mice reach sexual maturity at 45 - 60 days old, with an estrous cycle of 4 - 5 days.

Physical Maturity / Adulthood

At 60 - 90 days, mice enter adulthood.

Middle to Old Age

Mice enter middle age around 4 months and old age after 6 months. On average, healthy mice live 18 - 24 months, with a maximum of up to 3 years.

Interestingly, a mouse's short lifespan can be roughly correlated to the human average lifespan of about 80 years. Theoretically, 1 day in a mouse's life is approximately equivalent to 40 days in a human. Here are some stage - based conversions:

Weaning: Mouse 3 - 4 weeks is about like human 6 months.
Adolescence: Mouse 42 days is similar to human 11.5 years.
Adulthood: Mouse 10 weeks (at sexual maturity) is like human 20 years.
Middle Age: Mouse 15 months is about human 51 years.
Old Age/Senescence: Mouse 18 months is similar to human 70+ years.

Choosing the Right Age for Mouse Experiments

Mice's organs start maturing by 4 - 6 weeks. By 6 - 8 weeks, their organs are fully developed, and they're in good health, making this age suitable for most experiments.

Acclimatization

When ordering mice, it's wise to choose those 1 - 2 weeks younger than the required experimental age. This gives them time to acclimate to the laboratory environment.

Immunology Studies

If human cell line xenografts are difficult, 4 - 6 week - old mice can be a good choice. Their less - developed immune systems make tumor engraftment easier.

Breeding Experiments

For breeding, 9 - 10 week - old mice are recommended as they have a stronger reproductive capacity.

Aging/Geriatric Studies

Select mice 12 months or older to model physiological changes in the elderly.

By understanding these aspects of lab mice, you'll be better prepared to plan and execute your animal experiments effectively.