Abstract
BALB/c female mice were given a single sc injection of 5 IU PMSG at 16 : 00 hr and 48 hr later received a single ip injection of 5 IU hCG. Each gonadotropin-treated female was paired with one BALB/c male immediately after hCG injection. Copulation was observed in 28 (96.6%) of the 29 pairs. However, when two of the gonadotropin-treated females were placed with one BALB/c male in a single cage, copulation was confirmed consistently in only one of the two females. Possible explanations are proposed for the present finding that a single BALB/c male mouse does not copulate with more than one female over a single night.
