Laboratoire de Comportement Animal, CNRS URA 1291, INRA, 37380 Nouzilly, France.
The present study aimed at examining whether the orientation response of newborn rabbits can be influenced by olfactory cues acquired in utero. The pups' prenatal odor environment was manipulated by controlling the pregnant mothers' diet [control (Co) vs cumin-added (Cu) groups]. Prior to any postnatal ingestion, pups were submitted to absolute and relative preference tests in a 2-sided arena. The absolute preference tests consisted in presenting either a prenatal (placenta) or a postnatal substrate (colostrum) as opposed to a control stimulus (water). The relative preference test consisted in presenting simultaneously these prenatal and postnatal substrates. The substrates either matched or not the pups' prenatal olfactory environment. Results were as follows: Pups oriented longer to the side of the arena odorised with placenta (or colostrum) corresponding to the odor they were exposed to in utero: Cu-pups preferred the odor of a placenta (or colostrum) from a Cu-fed doe (during gestation) as compared to a placenta (or colostrum) from a Co-fed female, and conversely for Co-pups. In addition, pure cumin odor was attractive to Cu pups while it was repulsive to controls. Finally, pups did not differentiate placenta and colostrum odors when both were from a female of their own type. They behaved as if both pre- and postnatal substrates' odors were treated as chemosensorily and/or motivationaly equivalent. Rabbit pups are thus monitoring the dominant odor of their amniotic ecology and use it in their initial neonatal orientation behavior. Prenatal chemosensory experience may enhance the immediate efficiency of nipple localisation and condition the success of vital, initial sucking episodes.