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					Animal Resources Center


    BASIC MOUSE BREEDING
             &
    WEANING PROCEDURES
           Basic Mouse Breeding
            Reproductive 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
► 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 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
              •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
            •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
  scrotum   male. Note the
            presence of the
            scrotum.
          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
                            *The date of birth should be noted
  litters are successful.    on the cage card.
                     Mouse Pups




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




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




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




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




By 3 weeks of age
the pups become       These pups are
very active           3 weeks of age
(popcorn stage)       and ready to be
                      weaned.
             Weaning Policy
             Pairs vs. Trios
► Incages 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.

► Incages 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
    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.

Actual
date
weaning
should
have
occurred




Segments
                                                       # of cages

                                                       # of cages

                                                       # of cages

                                                       # of cages



     IMPORTANT: NOTE THE NUMBER OF CAGES IN THE “COMMENTS” COLUMN
                   Weaning
►   Place completed pink
    Temp Card on the new
    cage.                         Ermeling
                                  mouse/ Balb/c

                                  4♀
►   FILL IN ALL                    W12345 (note segment also)
    REQUESTED                     9/1/04

    INFORMATION.                  Date wean should have happened
                                  if not same date as “today’s date”


• Submit the completed “Wean Request Form” to the
ARC office for processing.
• Cage cards for weans are generated on Monday,
Wednesday, and Friday.
                     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)
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
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
 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
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

				
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