Placenta on pups' skin accelerates onset of maternal behaviour in non-pregnant rats

Previous research has indicated that virgin rats (Rattus norvegicus) behave maternally (sensitize) more rapidly if kept in close proximity with pups. Since both parturient rats and a large percentage of virgin rats avidly consume placenta, we tested whether placenta and amnionic fluid, applied to the skin of the stimulus pups, would draw the female adults into closer contact with the pups and therefore hasten the onset of maternal behaviour. The results indicated that the procedure indeed shortened the maternal sensitization latency. Furthermore, this effect was not due to the wetness of the pups, to the presence of placenta in the cage, or to the the adults having previously ingested placenta. Other attractive ingestibles applied to the pups' skin produced an intermediate, but not significant, shortening of the maternal sensitization latency.