basic

Animal Resources Center: 

Animal Resources Center BASIC MOUSE BREEDING & WEANING PROCEDURES

Basic Mouse BreedingReproductive Data: 

Basic Mouse BreedingReproductive Data Sexual maturity 40-60 days Estrous cycle 4 - 5 days Gestation 19-21 days Weaning age 21 days Reproductive life + or - 8 months Life span 1 - 3 years Pups begin eating dry food 12 -14 days Litter size 6-12 pups

Mating Systems: 

Mating Systems Timed mating Observed for presence of vaginal plugs Monogamous pairs 1 male to 1 female Trios 1 male to 2 females Harem Mating 1 male to 3 or more females Not recommended for standard mouse cage. If a trio or harem mating system is used, it is VERY important to REMOVE pregnant females from the group cage prior to their delivery.

Vaginal Plugs: 

Vaginal Plugs Vaginal plugs are NOT a guarantee of pregnancy. They are only an indication that copulation has taken place. This is important if timed mating is needed. The best time to look for plugs is in the morning since mating usually occurs during the dark cycle and plugs only remain in place for 10-15 hours

Sexing Mice: 

Sexing Mice The drawing at the top illustrates the difference in anogenital distance in male and female pups. The drawing at the bottom illustrates the difference in anogenital distance in adults. Also note the presence of the scrotum in the male.

Sexing Mice: 

Sexing Mice In the adult mouse, male and female are easily differentiated by the anogenital distance. The mouse on the left is female. The mouse on the right is male. Note the presence of the scrotum. scrotum

Mouse Reproduction: 

Mouse Reproduction First-time mothers are sometimes very careless with their young and mortality can be very high. It is not unusual for a first time mother to cannibalize her litter. In many cases, future litters are successful. *The date of birth should be noted on the cage card.

Mouse Pups: 

Mouse Pups 1 day old mice are very red, helpless and hairless. The ears and eyes are shut. If they are nursing, milk can easily be seen in the stomach. At day 2 the pups are less red, more pink Milk can still be seen in the stomach By day 3, the ear flaps will begin to open If the pups are going to be black or agouti, the skin pigment begins to develop

and more pups: 

and more pups On day 4 the ears are erect and milk is no longer visible in the stomach By day 5, the pups will begin to develop light, fuzzy dorsal fur At day 6 the fur is thicker across the shoulders and the coat color may be evident

and more pups: 

and more pups By day 7 the back of the pups is completely covered in fur. Day 8, the belly is beginning to show fur On day 9 the fur is thicker. Females will have five pairs of conspicuous nipples while the males will be much less obvious

and more pups: 

and more pups Day 10, the fur growth is complete and muscular activity is increased By day 11 the teeth are beginning to erupt and the eyes start to open. At days 12,13 and 14, the eyes are mostly open and they begin to nibble of solid food

and more pups: 

and more pups By 3 weeks of age the pups become very active (popcorn stage) These pups are 3 weeks of age and ready to be weaned.

Weaning PolicyPairs vs. Trios: 

Weaning PolicyPairs vs. Trios In cages with breeder pairs: If weanlings reach 25 days of age and have not been weaned, the ARC staff will wean them and a penalty will be applied. In cages with breeder trios: If weanlings reach 22 days of age and have not been weaned, the ARC staff will wean them. This allows a 1 day grace period after notification at day 21.

Weaning: 

Weaning A “wean request form” must be filled out when animals are weaned from the parent. Please fill in ALL information accurately and return to the ARC office. No more than four animals may be housed in the same cage. If separating by gender, use one segment for each gender. IMPORTANT: NOTE THE NUMBER OF CAGES IN THE “COMMENTS” COLUMN Segments # of cages # of cages # of cages # of cages Actual date weaning should have occurred

Weaning: 

Weaning Place completed pink Temp Card on the new cage. FILL IN ALL REQUESTED INFORMATION. Submit the completed “Wean Request Form” to the ARC office for processing. Cage cards for weans are generated on Monday, Wednesday, and Friday. W12345 (note segment also) Ermeling mouse/ Balb/c 4 ♀ 9/1/04 Date wean should have happened if not same date as “today’s date”

ARC Wean Policy: 

ARC Wean Policy Rodents should be weaned at 21 days old as a general rule. Realizing occasions arise that prevent someone from weaning on the specific date, a grace period of 3 additional days has been allowed. Cages with multiple litters, except those in large breeding cages, will not be given a grace period. Strains that routinely require delayed weaning (see discussion below) should be set-up as breeding pairs and not trios. When litters reach 21 days of age the ARC staff will e-mail the “PI” and the “contact” listed on the cage card to let them know there are mice to be weaned in the facility. The blitz should indicate the room number where litters are housed that are due for weaning. In addition the ARC technician will put a ”Please Wean” sticker on the cage card that indicates the date the ARC staff will wean the mice if not weaned by the lab, and indicates that a penalty fee will be charged. In cages with breeder pairs: If weanlings reach 25 days of age and have not been weaned, the ARC staff will wean them. In cages with breeder trios (or greater): If weanlings reach 22 days of age and have not been weaned, the ARC staff will wean them. Weaning at 22 days of age is to allow the lab a day to wean the mice after the e-mail notification.

ARC Wean Policy (continued): 

ARC Wean Policy (continued) In both of the above cases the lab will be assessed a penalty fee of $50 per litter weaned. The ARC technicians will NOT contact the lab prior to weaning on day 25 or 22 (see above), but will send the contact person an email to let them know that the weaning has already been done. The effective date on the wean request form should be the date they are weaned and placed in their own cages. The ARC technician will complete an MS slip indicating the number of litters weaned and the lab personnel responsible for the weaning for each litter. The ARC office will process the MS slip so that the bill will reflect the number of late weaning penalty fees that have been assessed for each lab technician or other laboratory personnel that are responsible for weaning. Please note that the Wean Number from the Wean Request Form needs to be clearly written on the pink temporary cards on each cage. If the contact name is different from the name printed on the breeding cage permanent card, please write the correct name on the temporary card. If the ARC staff has any questions about placement of cage cards, they will contact the name on the temporary card. It is necessary to note ‘Large Breeding Cage’ in the comments section of the wean form, otherwise everything is processed as regular cages

Delayed Weaning: 

Delayed Weaning If a member of the lab feels a litter will need to stay with its mother beyond the “grace period”, they should contact a member of the ARC veterinary staff for a weaning exception. If this weaning exception will be for a specific strain/line, the PI will be required to provide a written justification for this exemption. If delayed weaning is approved, the ARC will provide an ‘Approved Delayed Weaning’ card.

Cage Cards after Weaning: 

Cage Cards after Weaning In an effort to assure that cage cards are put on weaned mice in a timely fashion, the ARC asks the laboratory staff to pick-up the cage cards. The ARC office notifies the contact when cards are at the facility. The cards should be picked up and put on the appropriate cages within 24 to 48 hours. This is important so that we get the information required by the regulatory agencies onto the cages where it belongs, to prevent problems with billing, and to minimize loss of information written on temporary cards. If the cards are not on the cages within 1 week of weaning the ARC will put the cards on the cages for the laboratory. Please let the ARC office know who is responsible for weaning your mice and putting the cage cards on the cages, i.e. your lab or the ARC.

Contact Numbers: 

Contact Numbers Main office ~ 650-7592 Email: ARC@dartmouth.edu Veterinarian ~ Call the main office for the vet on call. Supervisor, Technical Staff ~ 650-7571 Delayed Weaning requests: Facilities Operations Manager 650-7598 ARC Technologist 650-7528