Upright standing in the laboratory rat--time expenditure and its relation to locomotor activity.

Various reports have discussed a minimal cage height of 14 cm in rat maintenance. Recommendations for heights between 18 and 22 cm have been proposed and partially put into practice. However, no quantitative data exist on the actual utilisation of higher cages by rats. Thus, upright standing in 19 and 30 cm high cages as well as locomotor activity on the floor was assessed in 54 rats using passive infra-red detectors. The results showed a continuously decreasing use of cage height. On average, adult animals exceeded even a height of 24 cm for 13.8 (strain ACI) and 5.2 (strain LEW and SPRD) minutes per day respectively, corresponding to 8.7 and 5.5% respectively of the locomotor activity on the cage floor. Obviously upright standings is an integral part of the laboratory rat's ethogram showing similar strain-dependent circadian rhythms as locomotor activity.