Ovariectomy attenuates aggression by female rats cohabiting with sexually active sterile males

Female rats were individually housed with a single castrated male with a testosterone implant that maintained sexual and aggressive behavior. At weekly intervals, the resident male was removed and an unfamiliar female intruder was introduced into the colony. Attacks, bites, on-top, and piloerection of the resident female toward the intruder were scored. Females whose level of aggression toward the intruder was substantial and stable were either ovariectomized or sham-ovariectomized. Aggression tests resumed 1 week postoperatively and continued for an additional 3 weeks. The results confirm that female cohabiting with a sterile male become aggressive. They also demonstrate that ovariectomy greatly attenuates but does not entirely abolish aggression toward an unfamiliar female intruder. The results appear to contribute to a growing body of evidence suggesting that the biological substrate and behavioral form of aggression by females housed with males (including that following parturition) is a hormone-dependent aggression which parallels testosterone-dependent social aggression of males housed with females.