We investigated the hypothesis that photoperiod information received during the prenatal and/or early postnatal periods influences subsequent development in collared lemmings. Pregnant lemmings were exposed to either a short [8:16-h light-dark cycle (8:16)] or long (22:2) photoperiod throughout gestation. On the day of birth, pups were cross-fostered to dams housed in either short or long photoperiod. After an 11-day experimental lactational period (LACT), all animals were transferred to an intermediate photoperiod (16:8), the response to which depends on prior photoperiod exposure. Pups remained on this photoperiod until death at postnatal day 90. Information received during gestation (GEST) influenced offspring growth, pelage color, guard hair length, presence of the bifid claw at weaning, testes mass at 10 wk postweaning, and serum prolactin (PRL). Parameters measured at weaning reflected directly the photoperiod experienced during GEST (e.g., short-day GEST pups had white pelage). Conversely, parameters measured at 10 wk postweaning reflected the change in photoperiod experienced between GEST and 16:8 (e.g., short-day GEST young had gray pelage, indicative of an increase in photoperiod). Information received during LACT influenced growth and the presence of the bifid claw at weaning.