Group size, cage shelf level, and emotionality in non-obese diabetic mice: impact on onset and incidence of IDDM.

We hypothesized that differential housing, shown to influence emotionality and health in infectious and neoplastic disease, would influence onset/incidence of diabetes in an autoimmune animal model of insulin-dependent diabetes mellitus (IDDM). Non-obese diabetic mice were assigned to same-sex groups of one, five, or eight animals/cage, counterbalanced across shelf level by sex and group. During weekly urine glucose testing, presence of behaviors indicating emotional arousal was recorded. Sex, group, and shelf level affected emotionality: males, animals housed alone, and those on the top of the rack exhibited higher emotionality. Emotionality and shelf level predicted IDDM in females only. Delayed onset of IDDM was associated with high emotionality and with being housed on the top of the rack. Group size had no significant effect on IDDM. Emotionality may be a mediating factor in animals genetically predisposed to develop IDDM. This variable and cage shelf level should be incorporated into the design of studies in which IDDM is the outcome.