Dehydration parameters and standards for laboratory mice

Abstract

Water deprivation and restriction are common features of many physiologic and behavioral studies; however, there are no data-driven humane standards regarding mice on water deprivation or restriction studies to guide IACUC, investigators, and veterinarians. Here we acutely deprived outbred CD1 mice of water for as long as 48 h or restricted them to a 75% or 50% water ration; physical and physiologic indicators of dehydration were measured. With acute water deprivation, the appearance and attitude of mice deteriorated after 24 h, and weight loss exceeded 15%. Plasma osmolality was increased, and plasma volume decreased with each time interval. Plasma corticosterone concentration increased with duration of deprivation. There were no differences in any dehydration measures between mice housed in conventional static cages or ventilated racks. Chronic water restriction induced no significant changes compared with ad libitum availability. We conclude that acute water deprivation of as long as 24 h produces robust physiologic changes; however, deprivation in excess of 24 h is not recommended in light of apparent animal distress. Although clearly thirsty, mice adapt to chronic water restriction of as much as 50% of the ad libitum daily ration that is imposed over an interval of as long as 8 d.

Figure 1.

Appearance and attitude scales.

Figure 2.

Weight loss (g; mean ± SE, n = 24) in mice housed on either static or ventilated racks and acutely deprived of water for as long as 48 h: experiment 1. Weight loss was determined as absolute change from initial weight. There was no statistical difference between static and ventilated racks. After 24 and 48 h of acute water deprivation, mice had lost approximately 12% and 18%, respectively, of their baseline body weight; 15% weight loss corresponds to approximately 5.4 g.

Figure 3.

Plasma osmolality (top panel), sodium concentration (middle panel), and corticosterone level (bottom panel) of mice deprived of water as long as 48 h: experiment 1. Caging types have been combined; data are given as mean ± SE (n = 42 to 45). Within a panel, bars marked with different letters differ significantly (P < 0.05); values that are marked with the same letter are not significantly different.

Figure 4.

Hematocrit (top panel), total protein (middle panel), and plasma renin activity (bottom panel) in mice deprived of water for as long as 48 h: experiment 1. Caging types have been combined; data are given as mean ± SE (n = 42 to 45). Within a panel, bars marked with different letters differ significantly (P < 0.05); values that are marked with the same letter are not significantly different.

Figure 5.

Body weight (g; mean ± SE, n = 13 or 14) in mice allowed ad libitum (100% ration) water intake or restricted to either 75% or 50% of that ration daily: experiment 2. The body weights of the 50% and 75% groups differ (P < 0.05) from controls and from each other on days 4 and 8 of restriction.