1Laboratoire de Comportement Animal, CNRS URA 1291, INRA, 37380 Nouzilly, France.
2Laboratoire de Recherche sur les Arômes, INRA, 21000 Dijon, France.
3Etablissement National d'Enseignement Supérieur Agricole, 21000 Dijon, France.
Previous studies have separately established the reactogenic power of surface odor cues from the lactating female's abdomen (Hudson & Distel, 1983, Behav., 79: 255) and from fresh rabbit milk (Keil et al., 1990, Physiol. Behav. 47: 225). The present study aimed to assess the relative reinforcing values of both of these odor substrates for newborn pups. In addition, the pup responses to a fraction obtained from rabbit milk (labelled thereafter RMP21) was compared to the above odor substrates. The behavioral assay consisted in a 2-choice paradigm, using an arena with 2 compartments under which odor sources were presented without contact. To determine the absolute and relative responses to the different combinations of stimuli, groups of pups were timed in the following tests: 1) a lactating female's abdomen (LFA) presented against a control stimulus (rabbit fur; RF); 2) milk (Mi) against a) a RF or b) a LFA; 3) RMP21 against either a) a RF, b) Mi or c) a LFA. In assay 1 (LFA vs RF), pups were attracted to the LFA indicating that lactating females emit attractive cues from their abdominal skin. Assay 2a (Mi vs RF) revealed that milk was attractive, and assay 2b (Mi vs LFA) further showed that it was as attractive as a LFA. Finally, RMP21 revealed to be attractive in an absolute choice test (assay 3a: RMP21 vs RF). When it was paired with the odors of a LFA (assay 3b) or of Mi (assay 3c), RMP21 elicited equivalent attraction responses than LFA and Mi. Conclusions: 1) the volatiles developing over the abdomen of lactating females and over rabbit milk inducing similar patterns of positive orientation in pups, it may be suggested that both sources carry functionally similar compounds; 2) the isolated RMP21 fraction from rabbit milk may in itself account for the attraction response of pups to both other stimuli.