Effect of a cage divider permitting social stimuli on stress and food intake in rats

Abstract

The need to obtain data from individual laboratory animals has forced many researchers to singly-house small animals. This is costly to the researcher and isolation can adversely affect animal physiology and behavior which in turn may threaten the validity and generalization of experiment results to humans. We assessed the practical use of a housing device - dubbed "Buddy Barrier" (BB) - that allows social stimulation in a paired-housing situation while at the same time permitting the collection of individual measures that traditionally require individual-housing. To assess stress responses to the BB, adult male rats were single or pair-housed for several days with and without a BB in the cage. Fecal corticosterone metabolites (fCORT), food intake and body weight were monitored daily. Plasma CORT and adrenal catecholamine levels were assessed at the end of the housing manipulation. Stress hormone measures did not differ in paired vs. singly-housed rats and paired rats quickly habituated to introduction and removal of the BB. Barring a trend for paired rats to eat more in the first 4 h of the dark, there was no difference in 24 h intakes or body weight gain between singly and paired-housed rats. While the BB attenuated 24 h intakes in both groups, intakes normalized to non-BB conditions by the third BB reintroduction. A device such as the BB can enhance the welfare of animals by providing social enrichment without compromising the integrity of experimental protocols traditionally requiring single-housing. In times of lagging research funding it can also substantially reduce housing costs.

Figure 1

Panel A) “Buddy Barrier” housing device used to avoid single housing of rats when individual measures such as food intake and fecal specimens are needed. Here it was also used in rats in the Isolated group to control for space restriction and novelty of the BB when the Paired group was exposed to it. Panel B) The BB allows for visual, audio, olfactory, and limited tactile contact between rats while food and feces are kept separated.

Figure 2

Panel A) Daily levels of corticosterone extracted from a 0.20g sample of feces (fCORT) excreted by Paired and Isolated rats over a 4hr period on days when the buddy barrier was in the cage separating the Paired rats (BB) and when not in the cage allowing full social contact in Paired rats (NoBB). The 0.20g sample from Paired rats with no BB consisted of a mixture of both rats’ feces. A 6-9 hr time between circulating and fecal CORT was considered when the values where plotted. Therefore the BB conditions specified under each value reflects secretion of CORT under that BB condition (e.g., the BB was actually placed into the cage on the morning of Day 7 but the fCORT value plotted for Day 7 reflects circulating CORT levels occurring with No BB in the cage so the value was plotted under NoBB). Groups differed only on Day 17 and 26 (*p<0.05). Panel B) Total fecal output collected from Paired and Isolated rats over a 4hr period with the buddy barrier in the cage (BB) and not in the cage (NoBB). E.g., on Day 7, the BB was placed in the cage and feces collected after 4hr with the BB in the cage.

Figure 3

Panel A) Daily Food intake during the first 4hrs in the dark of Isolated and Paired rats with and without a BB in the cage. There was no main effect of group across BB conditions but individual t-tests revealed increased intake in Paired vs. Isolated rats on some days (*p<0.05; **p<0.01, ***p<0.001). Panel B) Serial 24-hour chow intake of Isolated vs. Paired rats on days with the buddy barrier in the cage (BB) and without (NoBB). Days omitted (1, 6, 11, 16, 26, and 31) were Mondays, when no 24 hr data was obtained (Sunday-Monday). NoBB data for Paired rats were derived from the total intake of both rats in the cage divided by 2.

Figure 4

Panel A) Daily mean body weights of Paired and Isolated rats on days with the buddy barrier in the cage (BB) and without (NoBB). Panel B) Daily weight gain or lost in the groups across BB conditions. Omitted days were Mondays as weights were not recorded on Sunday to subtract from Monday’s weights; *p<0.05, **p<0.01 difference in weight gained between groups.