Ming, there are too many pitfalls in mouse breeding. Can you provide a comprehensive summary?

Let's discuss this from the perspectives of breeding failure and infertility.

 

Breeding Failure

 

Mating Management
 

1.Co-housing Duration:  Insufficient co-housing time may lead to inadequate mating opportunities. It is recommended to co-house male and female mice for at least 7 days.

2.Breeding Ratio:  Improper breeding ratios can affect success. The recommended male-to-female ratio is 1:2 to 1:3.

3.Breeding Pair Adjustment:  If no pregnancy occurs after 3 weeks of mating, breeding pairs should be adjusted promptly.

 

Physiological Defects
 

1.Reproductive System Abnormalities:  Female mice may have structural abnormalities such as double vagina, vaginal atresia, or unilateral uterus. Male mice may have genital abnormalities like cryptorchidism, monorchidism, or genital trauma. It is recommended to perform reproductive system examinations before breeding to exclude abnormalities.

2.Embryonic Lethality:  Certain genotypes may exhibit embryonic lethality, causing embryos to die at specific developmental stages. When selecting mouse strains, it is crucial to fully understand their genetic background and avoid strains with known embryonic lethality.

 

Genetic Factors
 

1.Genetic Drift:  Long-term inbreeding may lead to genetic drift, affecting reproductive performance. It is recommended to periodically introduce new breeding stock to maintain genetic diversity in the colony.

2.Substrain Divergence:  Mice bred independently in different laboratories or environments may develop substrain divergence. It is recommended to use mice from the same source whenever possible in experimental designs.

 

Environmental Factors
 

Noise and vibration, temperature and lighting, and cage environment all affect reproduction. For detailed information, please refer to the previous article "What to Do When Mice Are Pregnant? A Complete Guide to Gestation and Lactation Care."

 

Infertility
 

Male-Related Causes
 

1.Sperm Quality Issues:  Low sperm motility, dead sperm, or abnormal sperm morphology are common causes of male infertility. Semen analysis is recommended to assess sperm quality, and breeding males should be replaced if necessary.

2.Genital Abnormalities:  As mentioned above.

Female-Related Causes

1.Reproductive System Structural Abnormalities:  As mentioned above.

2.Poor Maternal Behavior:  Some female mice may refuse to nurse or care for their pups due to poor maternal instincts, leading to pup mortality. It is recommended to select breeding females with good maternal behavior.

 

Maternal Behavior Problems

Cannibalism
 

1.Stress Response:  Female mice may cannibalize their pups due to stress responses caused by environmental changes, noise, or human disturbance. It is recommended to minimize external disturbances during pregnancy and lactation.

2.Weak Pups:  Pups born with low vitality may be mistaken by the mother as sick or weak individuals, leading to cannibalism. It is recommended to check the health status of pups promptly after birth and provide artificial intervention if necessary.

 

Abandonment
 

1.Maternal Fright, Poor Pup Development, Poor Maternal Behavior:  Cross-fostering measures should be taken.

Cross-Fostering Measures:

●Select foster mothers with good maternal behavior and different coat colors. Their gestational age should be 1-3 days greater than that of the original mother.

●Remove the original mother's scent by rubbing the pups with bedding from the foster mother's cage, then place the pups into the foster mother's cage.

 

Weak Pups
 

1.Malnutrition:  Maternal malnutrition may lead to weak pups. It is recommended to provide adequate nutrition to female mice, especially during pregnancy and lactation.

 

Other Issues
 

1.Strain Contamination

Strain contamination refers to the accidental mixing of different mouse strains, leading to genetic contamination.

Solutions:

●Correctly fill out cage cards to ensure one-to-one correspondence during cage changes by animal care staff.

●Use ear punching methods to mark mice for easy identification.

1.Seasonal Breeding Decline:  Breeding capacity decreases in late autumn and winter.

2.Strain-Specific Breeding Differences:  For example, homozygous nude mice have relatively poor breeding capacity.

 

References:

[1] Peng, X., & Yin, H. (2021). Breeding strategies for genetically engineered mice. Experimental Science and Technology, 19(05), 31-37.

[2] Relevant encyclopedia entry on genetic concepts.

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