Effects of isolation rearing upon behavioral state organization and growth in the rabbit

Newborn rabbits were raised in isolation from Day 1 through Day 20 except for a daily 15-min feeding with the mother. They were returned to their littermates on Day 20 and remained with them until Day 30. On Days 2, 8, 16, 20, and 30, each isolate and a littermate control (group reared) were observed for 1 hr under standarized conditions. Every 10 sec a judgment was made of the animal's behavioral state. Food intake and body weight data was also obtained. In comparison to controls, isolation-reared rabbits spent significantly less time in Wake on Days 16 and 20, they spent more time in Active Sleep than in Quiet Sleep, and they had more visits to Active Sleep. Isolates also ingested less milk, had a slower rate of weight gain, and were less efficient in utilizing the food they ingested. The state findings are discussed with respect to Roffwarg, Muzio, and Dement's (1966, Science 152, 604–619) hypothesis concerning the function of Active Sleep. In general, the isolate animal differs from its group-reared control both quantitatively and qualitatively.