Studies on the estrus cycle of the ground squirrel (Citellus citellus L.) at experimentally induced hibernation

Eighty-five ground squirrels (C. citellus L.) were examined immediately after arousal (March-June). It was established that the animals were in estrus at the end of March; in April they were pregnant; in May they were in lactation; and in June they were already at rest, a postlactation period. Fifteen ground squirrels were treated with Hibernal and then placed in a chamber for 30 days at external temperature, 8-12 degrees C. In this case the estrus cycle of hypothermic ground squirrels was not changed. A retarded involution of corpus luteum persisted for a month and cystic follicles appeared in the ovary.