Warmth from skin-to-skin contact with mother is essential for the acquisition of filial huddling preference in preweanling rats.

During a single, 2-hr session with a scented foster dam, preweanling rat pups form an affiliative attraction to an odor associated with the maternal caregiver, manifest as a huddling preference. To identify maternal stimuli that induce this filial preference, we quantitatively examined behavioral interactions during odor conditioning. Bout duration of skin-to-skin (STS) contact was positively associated with the preference. In contrast, simple physical contact and anogenital licking were not significantly related to the preference. The frequency of nonanogenital licking was negatively associated with the preference as well as with bout duration of STS contact. When odor conditioning was conducted with a warm cylinder, ambient warmth, or stroking as the unconditioned stimulus, only pups exposed to the warm cylinder exhibited a preference for the conditioned odor. These results suggest a positive, affiliative effect of maternal STS contact on pup filial preference, which may be disrupted by maternal licking.