All standards used to care for the mice conform to the Guide for the Care and Use of Laboratory Animals (1996), which includes general requirements for vertebrates, for warm-blooded animals, and for mice in particular. These particular issues are identified as areas to review by the USDA Inspection Report, subchapter A-Animal Welfare, subpart F as specifications for the humane handling, care, treatment, and transportation of warm blooded animals other than dogs, cats, rabbits, hamsters, guinea pigs, nonhuman primates, and marine mammals [1997 edition].
Mice used for teaching and research in Psychology Department at Carleton are from the strain C57BL/6j and are purchased from the Jackson Laboratories (in US). Because at Carleton we study development we breed mice. Thus, the animal colony ranges from newly born pups to adults. Pups are kept in cages with their dams up until post-natal day (PND) 21. Since mice are social animals at PND 21 they are weaned by sex (i.e. males and females are placed in different cages) and placed in cages with up to five age-matched mice that are from their same litter. Mice become adults at approximately 3-6 months of age, and their life span is between 1 to 3 years. The typical weight for newborns 1.0 g and for adult mice is 20-40 g.
Housing
Mice are housed in a room with a 12 hour light/12 hour dark cycle that is set to allow researchers to collect data during the day. The lights are on at 7 am and off at 7 pm. The lights should not be switched on to override the light/dark cycle except in cases of emergency, and then the switching should be recorded.
The room is maintained between 70-72 degrees F and its air is circulated 12 times per day. Filters aid in the ventilation and need to be changed 2x per month to maintain good air quality and good circulation. Robyn Durand, the animal care manager for psychology, trains staff on how to change the air filters, and keeps track of the changing of them on a chart in the office area.
The information about weight of mice and size of cage, from the Guide is provided below:
- Mice less than 10 should have a floor area of 6 inches squared and a height of 5 inches.
- Mice up to 15 g should have a floor area of 8 inches squared and a height of 5 inches.
- Mice up to 25 g should have a floor area of 12 inches squared and a height of 5 inches.
- Mice over 25 g should have a floor area over 15 inches squared and a height of 5 inches
The size of current mouse cages that we use at Carleton are 10 1/2” (width) x 19” (length) x 6 1/8” (height) inches, which includes a total of 199 inches squared. The cage is a rectangular style made of Polycarbonate with a wire bar lid used to hold the water bottle and feed. The cage perfectly supports litters that have not been weaned. When dams give birth, all pups must be kept with the dam from post-natal day (PND) 0 to PND 21 to avoid disturbing the litters and mouse development. PND 21 mice must be weaned and placed in different cages by sex. The cages can hold at up to five 25 g mice with no problem. Additionally, pelleted paper bedding at least 2 in deep is placed in each mouse cage to allow for mouse comfort as well as easier cleanup of urine and feces.
Animal Identification
Adult mice are usually kept five to a cage by sex, that is, males and females are kept in different cages, and are labeled by numbers on a card that exists outside the cage. The card also includes the investigator’s name, the date of birth, and the date of acquisition, and any invasive procedures that were done. The mice inside the cage may be differentiated by a permanent marker stripes or dots on the tail (e.g. mouse no. 1 has one dot on the tail, mouse no. 2 has two dots on the tail and so and so forth). No other invasive technique (i.e., ear punching) is used at Carleton for identification. Mice may be differentiated by a permanent marker after weaning (PND 21).
Enrichment
Enrichment for mice is used for at least three purposes, including building nests for pregnant dams, comfort, and/or “playing.” Enrichment used for building nests includes Enviro-dri and nestlets. Enrichment used for housing and/or playing includes mouse igloos and tunnels (that are made of cardboard and/or plastic).
Food and Water
Water consumption is 4-7 ml, or 1.5 ml/10 g of body weight daily. Food consumption is 4-5 g a day (12 g/100 g body weight per day). Water is offered freely to the animals to allow for a good level of consumption. Food is offered freely, except when mice are in experiments in which they are motivated to find food or eat.
Daily Chores
Daily checking includes checking water, food, and animal health. Each is described below.
Mice are commonly fed and watered freely (ad libitum). Water bottles are checked daily, and refilled with each bedding change (2x per week) and sanitized by the cage washer. They are also topped off if needed during daily checks. Food amounts are also checked daily and replenished as needed. Pelleted rodent chow (irradiated with 18% fat) purchased from the company Envigo is the diet for mice. This food supports gestation, lactation and growth.
During food/water check, one should take a look at each mouse to make sure each is doing well. Mice should appear to be moving, and to sniff and orient to you. If there is any sign of blood, any wounds, or if an animal does not move easily when the cage is moved, call Robyn Durand (phone numbers provided in the animal facility) and leave a message for her to respond. You must also call the faculty investigator (Gisel Flores-Montoya). She will take action and call the veterinarian if necessary, to examine the animal.
Periodic Chores
Mouse’ cages should be cleaned 2x per week, with bedding removed, cages washed in the cage washer at a sanitizing temperature with disinfectant solution, and new bedding put in. The mouse room should be swept and mopped with disinfectant solution once every week. The weighing table should also be wiped down every week. Shelving, walls, and cage racks should be sanitized at least once every term.
For Handling instructions, see the section on Safety Measures While in Contact with Mice