Grims, C., Jacobson, C., Hedenqvist, P. 2021. Are female mice dehydrated during peak lactation? Effect of water and gel supplement on hydration parameters and water consumption in two strains of mice. Scandinavian Journal of Laboratory Animal Science 47(3), 16-24.

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.

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