Mice (Mus musculus) have a high basal rate of metabolism which increases during pregnancy and lactation. During peak lactation, water intake amounts to up to 65 % of the bodyweight per day. Providing water in a bottle may pose a restriction of water intake and lead to dehydration during periods of high demand, such as peak lactation. To establish if female mice are able to sustain a physiological hydration status during peak lactation, a completely randomized factorial design study was conducted with 12 RjOrl:SWISS (SWISS) and 12 C57BL/6JRj (B6) six-week old female mice in breeding. Female mice were randomly assigned to one of three groups with different watering alternatives: water bottle (Standard, n=6); water bottle + sachet with 98 % water gel (Gel, n=6); or water bottle + water bowl (Bowl, n=6). Non-mated females, provided with water bottles, served as controls (n=6). Hydration parameters [total protein (TP), hemoglobin, hematocrit, serum osmolality (Osmol), blood urea nitrogen (BUN)] and magnesium were measured in blood before mating (Pre) and during peak lactation (Peak), and at the same time points in controls. Water bottles were weighed during lactation and body weights of females and litters recorded at weaning. Data were analyzed by parametric or non-parametric methods to evaluate effects of strain, group and time point. The hydration parameters and magnesium were mostly within normal ranges in all animals at Pre and Peak. TP was lower at Peak in all lactating groups compared to Controls and to Pre (p<0.01). Mice in group Bowl consumed 54 % less bottle water compared with Gel and Standard (p<0.001), had 34 % lower levels of BUN than Standard and Control (p<0.01) and 5 % lower serum osmolality at Peak than Pre (p<0.01). Conclusion: Female mice are not dehydrated at peak lactation. However, they prefer to drink, and seemingly drink more water, from a bowl than from a bottle.

Handling laboratory animals for husbandry and other procedures can be an important source of anxiety and stress, compromising animal welfare as well as the reliability of research that is sensitive to background stressors. Studies have revealed that picking up laboratory mice by the tail induces aversion, anxiety, physiological stress and depression-like behaviour, but such negative responses can be reduced substantially by using a handling tunnel that mice enter readily with minimal familiarisation. It has not been tested whether anxiety and aversion can be reduced similarly by using other objects to lift up mice from their home cage. Here we compared the willingness of C57BL/6NRj mice to interact voluntarily with their handler after being picked up either on a plastic ladder present in the home cage, or inside a familiar tunnel, or lifted by the base of the tail and then returned to the home cage. We also tested anxiety in open field and elevated plus maze tests once animals were familiarised with their assigned handling method. While mice picked up briefly by the tail were unwilling to interact with the hand that picked them up, mice picked up by ladder or tunnel readily approached, climbed on or entered these devices, with no significant difference in time spent with ladder or tunnel. Anxiety in an unfamiliar open field was reduced to a similar extent in ladder and tunnel handled mice compared with those picked up by the tail. Mice handled by tunnel also showed reduced anxiety in an elevated plus maze compared to those handled by tail, while ladder handling resulted in an intermediate response. Our study shows that, like tunnels, using home cage ladders to pick up mice reduces anxiety and avoids the aversion that is induced by picking up mice by their tails. We discuss the potential practicality of using ladders and tunnels to handle mice in different contexts.