ALAT Breeding and Reproduction 2 — Questions and Answers
Question 1: What is the typical estrous cycle length for a mouse?
- 24 hours
- 4-5 days (Correct answer)
- 14-16 days
- 28 days
Correct answer: 4-5 days
The mouse estrous cycle is approximately 4-5 days with four stages: proestrus, estrus, metestrus, and diestrus.
Stages: proestrus (12-14 hours), estrus (12 hours, mating receptivity), metestrus (21 hours), and diestrus (48+ hours). Mice ovulate spontaneously during estrus. Post-partum estrus occurs within 24 hours of delivery.
Question 2: What is a vaginal plug and what does it indicate in mice?
- A sign of infection
- A coagulated mass of seminal fluid indicating mating has occurred (Correct answer)
- A contraceptive device
- A sign of urinary obstruction
Correct answer: A coagulated mass of seminal fluid indicating mating has occurred
A vaginal plug is coagulated seminal fluid that forms after mating. Checking for plugs each morning is standard for detecting mating in timed breeding.
Plugs form from male coagulating gland secretions and remain 8-24 hours. A plug found in the morning is designated gestational day 0.5. However, a plug does not guarantee pregnancy — 10-20% of plugged females don't become pregnant.
Question 3: What is the typical litter size for laboratory mice?
- 1-2 pups
- 6-12 pups (Correct answer)
- 15-20 pups
- 25-30 pups
Correct answer: 6-12 pups
Laboratory mice typically produce 6-12 pups, varying by strain. C57BL/6 average 6-8 pups; CD-1 outbred may produce 10-14.
First litters tend to be smaller. Pups are typically weaned at 21 days, separated by sex, and ear-punched for identification. Minimize cage disturbance during the first 48 hours to prevent cannibalism.
Question 4: What is the Whitten effect in mouse breeding?
- Females reject males during light cycle
- Male pheromones synchronize estrous cycles in group-housed females (Correct answer)
- Males become infertile with multiple females
- Females produce larger litters in enriched environments
Correct answer: Male pheromones synchronize estrous cycles in group-housed females
The Whitten effect occurs when male pheromones synchronize and stimulate estrous cycling in group-housed females within 3 days.
Mediated by male urinary pheromones detected by the female vomeronasal organ. Related effects: Lee-Boot (grouped females without males show suppressed cycles) and Bruce effect (strange male pheromones cause pregnancy block).
Question 5: At what age are mouse pups typically weaned?
- 7-10 days
- 14 days
- 21 days (Correct answer)
- 35 days
Correct answer: 21 days
Mouse pups are typically weaned at 21 days when they can eat solid food and drink independently. They should be separated by sex.
At weaning, pups weigh approximately 8-12 grams. Key steps: separate from dam, sex the pups, separate by sex, identify individually, and record. Some strains may need extended weaning up to 28 days.
Question 6: Why avoid disturbing a mouse dam's cage in the first 48 hours after birth?
- The cage is sterile
- Disturbance can cause the dam to cannibalize pups due to stress (Correct answer)
- Pups need darkness
- Cage changing isn't due yet
Correct answer: Disturbance can cause the dam to cannibalize pups due to stress
Disturbance within 48 hours of birth can trigger stress-induced cannibalism. Minimize disturbance during this critical bonding period.
Cannibalism is most likely in first 48 hours, especially in primiparous dams and C57BL/6 strain. Triggers include cage changing, loud noises, and unfamiliar odors. Delay cage changes until day 3-4 postpartum.
ALAT Breeding and Reproduction 2
What is the typical estrous cycle length for a mouse?