n. the effect that chemical signals (i.e. urinal pheromones) have in blocking the pregnancy of female rodents. Being exposed to the odor of an unfamiliar male causes laboratory mice (Mus musculus) to go through a miscarriage, after which follows their mating. First described by British endocrinologist Hilda Bruce in 1959. See whitten effect- also pregnancy block.
BRUCE EFFECT: "The Bruce effect is a phenomenon which terminates pregnancy in lab mice who are exposed to the new scent of unfamiliar males."