Do Laboratory Mouse Females that Lose Their Litters Behave Differently around Parturition?

Abstract

Efficiency in laboratory mouse breeding is hampered by poor reproductive performance, including the loss of entire litters shortly after birth. However, the underlying mechanisms are not yet fully understood and establishing the cause of death in laboratory mouse pups can be complicated. Newborn mouse pups are generally hidden in nests, dead pups are often eaten by the female, and the widespread practice of leaving periparturient females undisturbed complicates inspection, which may delay the discovery of pup loss. In order to efficiently prevent problems with litter loss, it is important to find key factors for survival. We investigated differences in periparturient behavior between female laboratory mice whose pups survived until weaning and females whose entire litters were lost. Video recordings of 82 primiparous females of the C57BL/6 strain or knockouts with C57BL/6 background were used. The mice were observed from 24 h before until 24 h after parturition and female behaviors coded using a pre-established ethogram. The relationship between behavior and survival was analyzed using logistic models, where litter survival was regressed on the proportion of 30-s observations with at least one occurrence of the behavior. We found that females with surviving litters performed more nest building behavior during the last 24 h before parturition (p = 0.004) and spent less time outside the nest during the entire observation period (p = 0.001). Increased litter survival was also associated with more passive maternal behaviors and the female ignoring still pups less. Females that lost their litters performed more parturition-related behaviors, suggesting prolonged labor. The results indicate that maternal behavior plays a significant role in laboratory mouse pup survival. Complications at parturition also contribute to litter mortality.

Fig 1. Observed relationship between female laboratory mouse behaviors and litter survival.

Nest building, parturition-related behavior, active and passive maternal behavior, ignoring still pup and being outside nest from 24 h before until 24 h after parturition in 64 primiparous mice whose litters survived (solid line; n = 49) and did not survive until weaning (dashed line; n = 15); mean proportion of 30-s observations per 6-h period with at least one occurrence of the behavior.

Fig 2. Predicted relationship between female laboratory mouse behavior and litter survival according to a multivariable logistic model.

Nest building during 24 h before parturition (left) and being outside nest from 24 h before until 24 h after parturition (right) in 64 primiparous mice; behaviors expressed as mean proportion of 30-s observations with at least one occurrence of the behavior, shaded areas are 95% confidence intervals.