Interlitter variability in fetal body weight in mouse offspring from continuous, overnight, and short-period matings.

When female mice of the Jcl:ICR strain were mated with a male either (1) continuously throughout the day or (2) overnight or (3) during 2 hours in the morning at light period, the interlitter variability of fetal body weight on the 18th day of gestation was smallest in the group with short-period mating. Thus, in the embryonic stage-specific teratological experiments, this mating schedule is advised. Even for routine reproductive toxicity testing protocols, the short-period mating may be preferable for the purpose of increasing test sensitivity.