Rodent Breeding
III. Husbandry Procedures
B. Rodent Breeding
PURPOSE
This protocol describes general procedures used by the College of Charleston for breeding rodents in the Vivarium of the Hollings Science Center. The specified activities pertain only to the breeding of rodent species (Rattus spp, and Mus spp) by the IACUP for animals intended for teaching purposes.
DEFINITIONS
Breeding- sexual propagation of animals.
Estrus- a female is sexually receptive to a male; ovulation occurs (duration approximately 12-14 hours for Mus spp and 13-15 hours for Rattus spp).
Feeding- ad libitum (constant access) availability of food.
Nestlets- two Kimwipes rolled into a ball or fluffy pine shavings may be used as nesting materials.
Outbreeding- a carefully planned scheme in which only unrelated animals of the same stock are mated.
Watering- ad libitum availability of water.
Weaning- separation from mother at 21 days of age.
BREEDING PROCEDURES
Initial Considerations
All animals will be maintained on a 14:10 light: dark cycle; this light cycle is best for breeding, as it helps females establish consistent estrous cycles. Animals will be acquired from an AAALAC-accredited vendor for the purposes of breeding. Breeding female rats will be at least 70 days of age when acquired for breeding and female mice will be 70 days of age.
PROCEDURES
Housing
Animals will be housed and cared for with food and water available ad libitum according to Animal Program Standard Operating Procedure III.A: Husbandry Procedures. Breeding animals will be maintained in a separate room in a quiet area.
Mating
See the Summary Table of Reproductive Parameters below.
Timed (hand) mating will be used for all animal pairing. Each female will be bred one or two times and only with outcrossed males. Only one adult male and one adult female rodent will be paired per cage, and these animals will remain together for 8 days (this amount of time is usually sufficient for mating to occur).
Monitoring
Once an animal has been mated, the female will be singly housed, and she will be monitored for evidence of pregnancy. Abdominal distention is apparent in most animals by 12-14 days of gestation, although animals with larger litters may show distention slightly earlier. In addition, it is possible to determine if the animal is pregnant by very gentle palpation of the abdomen at 12-14 days. If the animal is pregnant, a series of beads may be palpated on either side of the abdomen at 12-14 days after mating.
The cage(s) will be checked daily for a new litter near the anticipated date of birth. Staff will be instructed to notify the IACUP Director when birth occurs. Cage changes will be minimized prior to term (gestation 18-21 days in Mus spp; 21-23 days in Rattus spp) and postpartum. Nestlets will be provided 2-3 days prior to parturition. Following birth, newborns will be handled only minimally. Additionally, newborns will not be directly touched; they will be moved along with the bedding they are in using gloved hands for the first week after birth if cage changes are necessary. A litter of animals will be counted as one animal for the daily animal census until weaning.
Weaning
Weaning will occur at 21 days of age. Near the weaning date, food will be placed in the bottom of the cages to facilitate this transition, and long sipper tubes will be used on all water bottles for all recently weaned animals. Sexes will be separated into cages of 5 animals or less with food available on the floor of the cage for the first week. Sex will be determined by the anogenital distance; sex determination will be checked twice more during the next 7 days to ensure that the designation is correct. At this time, weaned animals will be renamed with a new stock name for in-house bred animals and will be moved out of the breeding room. At 45 days of age, they will be separated into same sex pair housed cages or individual housing, if specified by an approved protocol.
REFERENCES
Canadian Council on Animal Care, Guide to the Care and Use of Laboratory Animals, Second Edition, Appendix 1, Housing and Environment, pps 167-168.
National Research Council, Guide for the Care and Use of Laboratory Animals, H.H.S., N.I.H. Pub. No. 85-23, 2011 edition or succeeding editions.
Poole, T. (Ed.). (1999). The UFAW Handbook in the Care and Management of Laboratory Animals (7th ed.) Volume I Terrestrial Vertebrates. Malden, MA: Blackwell Science, Inc.
Summary Table of Reproductive Parameters
Mus spp
| Estrus Cycle (Range) | Duration of Estrus | Age at First Mating | Age at End of Mating | Life Span | Gestation Period | Litter Size | Weight of Newborn | Weaning Age | Age at Sexual Maturity |
|---|---|---|---|---|---|---|---|---|---|
| 2–9 days | 12–14 hours | 56–70 days | 6–12 months | 1–3 years | 18–21 days | 6–12 | 0.5–1.5 grams | 21 days | 56–70 days |
Source: Baumans, V. (1999). The Laboratory Mouse. In Poole, T. (Ed.). The UFAW Handbook on the Care and Management of Laboratory Animals (7th ed.) Volume I Terrestrial Vertebrates (pp. 282-312). Malden MA: Blackwell Science, Inc.
Rattus spp
| Estrus Cycle (Range) | Duration of Estrus | Age at First Mating | Age at End of Mating | Life Span | Gestation Period | Litter Size | Weight of Newborn | Weaning Age | Age at Sexual Maturity |
|---|---|---|---|---|---|---|---|---|---|
| 4-6 days | 13-15 hours | 50-100 days | 9-24 months | 2-4 years | 21-23 days | 3-18 | 4.5-6.0 grams | 21 days | 40-50 days |
Approved: April 5, 2001
Revised: April 19, 2001
Revised: September 11, 2001
Reviewed: August 24, 2012
Revised and Approved: September 27, 2019