All the Pups We Cannot See: Cannibalism Masks Perinatal Death in Laboratory Mouse Breeding but Infanticide Is Rare

Area of Science:

• Animal Science
• Laboratory Animal Science
• Reproductive Biology

Background:

• Perinatal mortality significantly impacts laboratory mouse breeding efficiency.
• Accurate assessment of pup survival is crucial for reliable research outcomes.
• Traditional counting methods may not fully capture all causes of pup loss.

Purpose of the Study:

• To compare the accuracy of a daily check method versus a video tracking method for estimating perinatal mortality in C57BL/6 mouse pups.
• To investigate the incidence of cannibalism and infanticide in different breeding setups.
• To identify critical periods of pup loss in laboratory mouse litters.

Main Methods:

• Comparison of a daily check (DAILY_CHECK) method with a video analysis (VIDEO_TRACK) method across 193 litters.
• Analysis of 109 litters using video recordings to assess cannibalism and infanticide.
• Statistical analysis using linear mixed models, Kaplan-Meier method, and logistic regression.

Main Results:

• The DAILY_CHECK method underestimated mean litter size by 35% and reported half the number of dead pups compared to VIDEO_TRACK.
• Pup loss risk was significantly higher in overlapping trios (TRIO-OVERLAP) versus non-overlapping trios (TRIO-NO_OVERLAP).
• Most cannibalism events involved already deceased pups, and infanticide was infrequent; substantial pup loss occurred before the first cage check.

Conclusions:

• Daily checks significantly underestimate perinatal mortality in laboratory mice.
• Video tracking provides a more accurate assessment of pup survival and loss, revealing higher mortality rates.
• Breeding facilities may be unaware of their true mouse pup mortality rates due to limitations in current monitoring methods.