Changes in responsiveness to kit odours across pregnancy: relevance for the onset of maternal behaviour

Abstract

Virgin does are indifferent to foster kits but lesions to the main or accessory olfactory systems allow them to behave “maternally” (i.e., they crouch over the litter and allow suckling). This suggests that kit-derived olfactory cues are aversive to virgins but not to lactating does. We hypothesised that the valence of such olfactory cues changes throughout gestation so that, at parturition, does are attracted to the newborn and can then show placentophagia, clean the kits and nurse them. To explore this hypothesis we exposed does to 2 nest boxes containing a variety of pup-derived vs. “neutral” odours, quantifying the number of sniffs and entrances to each box over 60 min. Virgins, confronted with 2 different types of contrasts, showed no significant differences in the number of sniffs or entrances directed at any of the 2 boxes. Pregnant rabbits sniffed the “kit-odour” box significantly more than the “neutral” one as early as gestation day 7, depending on the animals’ experience with the experimental setup and kit odours as virgins. The number of sniffs declined in late pregnancy in all groups. Entrances into the “kit-odour” box were few and significantly higher than those shown towards the “neutral” box only in 1 group. Our findings agree with a correlation between a shift in the valence of kit-derived olfactory cues and the hormonal changes known to occur throughout pregnancy. The relevance of this phenomenon for the onset of maternal responsiveness at parturition is discussed.