Ming, how does the mouse breeding process work?

 

The mouse breeding process mainly includes selecting breeding stock, co-housing, and pregnancy detection, among other stages.

 

I. Selecting Suitable Breeding Stock
 

Choosing appropriate breeding stock is fundamental to breeding success. Here are some key assessment points:

● Physical Examination: Select mice with glossy, smooth fur and no hair loss. Mice with strong limbs and agile reactions typically have good health. Prioritize mice with bright, clear, black eyes, and avoid those with cataracts or squinting in one eye.

● Health Status: Natural orifices (e.g., eyelids, nostrils, ear canals) of breeding mice should be free of secretions. Mice with a strong appetite and black, wheat-grain-shaped feces are healthier. Avoid mice with diarrhea due to gastrointestinal infections.

● Reproductive Capacity: Female mice should be selected at 6 weeks of age, as 6-8 weeks is the sexual maturity period for females. Male sexual maturity occurs slightly later; choose males at 8 weeks of age as breeding studs. Important checks: examine females for a double vagina or absence of vagina, and males for absence of penis or testicles.
 

II. Co-housing
 

Select sexually mature, healthy male and female mice for mating. To increase conception rates, the male-to-female ratio for co-housing can be 1:2 to 1:3.

There are two main co-housing methods:

1.  Continuous Co-housing: Female and male mice remain in the same cage for several consecutive days.

2.  Intermittent Co-housing: One female is housed with one male for a day, then replaced with another female.

To improve pregnancy rates, continuous co-housing can be used, with vaginal plug checks performed in the morning and afternoon. Earlier mating allows for more breeding generations. It is recommended to complete breeding before mice reach 4 months of age.

How can I tell if mating was successful?
 

III. Pregnancy Detection
 

1.  Vaginal Plug Check: 10-12 hours after mating, check the female's vagina for a vaginal plug. Use forceps to directly inspect the vagina for the presence of a plug (a whitish, solid gelatinous mass at the vaginal opening, formed by the coagulation of secretions from the male's seminal vesicles and coagulating glands within the vagina).

a.  Drawback: Susceptible to missed detection and pseudopregnancy.
 

2.  Sperm Detection via Vaginal Smear: Check the morning after co-housing. Using a disposable pipette tip moistened with a small amount of saline, insert it into the female's vagina, aspirate a few times, smear onto a slide, add a drop of saline, cover with a coverslip, and observe under a microscope. The presence of numerous motile sperm indicates fertilization.
 

IV. Identification and Record Management
 

Accurate identification and record-keeping help manage the mating process and ensure breeding plans proceed smoothly:

● Identification Method: Each mouse entering the facility should be marked, typically by ear punching, with each mouse assigned a specific identification number and corresponding genetic information. Previous articles have discussed mouse numbering; you can learn more by searching related resources.

● Record Content: Detailed records should include the genotype of breeding stock, mating times, vaginal plug check results, pregnancy status, and genotyping results of offspring. These records help track breeding progress and assess the reproductive performance of breeding stock.

Problems inevitably arise during mating. Addressing them promptly can prevent breeding failure.
 

V. Mating Problems
 

Accurate identification and record-keeping help manage the mating process and ensure breeding plans proceed smoothly:

● Male Aggression Towards Females: Reduce stocking density—a maximum of 5 mice per cage, preferably 3 when possible. Enrich the mice's environment by providing nesting material and toys to help alleviate stress.

● Female Refusal to Mate: Ensure the female is in estrus, determined by observing behavior and vaginal smears. If a female persistently refuses to mate, consider changing the male or adjusting the housing environment.
 

VI. Breeding Cage Culling and Replacement
 

● Criteria for Culling Cages: Cages where breeding has not resulted in pregnancy or viable pups for over 2 months, or where no litter has been born 2 months after the last birth, or where cannibalism has occurred in 2 consecutive litters, should be culled. This is often due to poor reproductive performance or poor nursing ability of the breeding pair, and culling is recommended.

● Criteria for Cage Replacement: For cages co-housed for over 6 months, the breeding pair is typically 7-8 months old. At this age, reproductive performance declines significantly or is even lost. It is recommended to select younger breeding stock of the same strain for replacement to ensure stable genetic inheritance of the colony.

 

References:

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

[2] Zhang Gongchang, Deng Yiping, Dong Birong. Husbandry, breeding, and identification strategies for genetically engineered mice. Modern Clinical Medicine, 2023, 49(04), 295-298.

[3]https://www.zhihu.com/question/31443264/answer/52190560?from=profile_answer_card

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