[xoxoxoBruce]

The Bruce effect, or pregnancy block, is the tendency for female rodents to terminate their pregnancies following exposure to the scent of an unfamiliar male.

The effect was first noted in 1959 by Hilda M. Bruce, and has primarily been studied in laboratory mice (Mus musculus). In mice, pregnancy can only be terminated prior to embryo implantation, but other species will interrupt even a late-term pregnancy.

The Bruce effect is also observed in deer-mice, meadow voles, collared lemmings, geladas, and it has also been proposed, but not confirmed, in other non-rodent species such as the lion.