[The establishment of pathogen-free colonies of Chinese and Syrian hamsters (Cricetulus griseus and Mesocricetus auratus) by foster rearing].

Naturally born (less than 5 d old) or hysterectomy-derived litters from 7 mice, 90 Chinese and 19 Syrian hamsters were fostered to conventional or gnotobiotic mouse, Chinese hamster or rat dams. Generally, Chinese hamsters and mice are able to serve mutually as foster mothers without special manipulations of dams or pups. Chinese hamsters adopted suckling mice with less problems than mice when fostering young hamsters. In correlation with sucking activity the growth of most of the mouse-fostered Chinese hamsters stopped during the first week after the pup exchange. During this phase only animals with high vitality could survive. When fostered by mice or rats, hysterectomy-derived (gnotobiotic) or newborn Chinese and Syrian hamsters survived only for few days. After initially intensive maternal care the hamster pups were increasingly neglected by the foster dams. This wellknown behavior is explained with the low sucking intensity of hamsters causing the decrease of the foster mother's maternal behaviour depending on the litter's stimuli. By this interaction between the mouse's maternity and the sucking behaviour of the hamster the success of the "classic" method of rearing gnotobiotic hamsters became highly chance dependent.