LABORATORY ANIMAL MEDICINE AND SCIENCE - SERIES II ...

V-9042 RATS AND MICE: Care and Management 1748. Health surveillanceThe health status of incoming animals and long termcolony residents can be assessed through serologicand microbiologic testing, as well as necropsy andhistopathologic examination. Specimens for laboratoryexamination can be obtained from incoming animalsat the time of delivery or from sentinel animals housedwithin long-term animal holding rooms. Sentinelanimals do not receive experimental treatments, butshould be handled at least as frequently as testanimals. Placing samples of soiled bedding fromseveral cages into the sentinel cages facilitatesexposure to latent infections that might be present inthe room. For examples of serologic panels for virusesin rats and mice and a discussion of viral healthsurveillance, see V-9044: Rats and Mice-ViralDiseases in this series.49. Section title BREEDING50. Gender determinationGender can be determined by comparing the distancebetween the genital papillae and the anus. Thisanogenital distance is greater in males than infemales. A vaginal closure membrane is present inyoung rat and mouse females, which usually opensaround 35 days of age in mice and around 72 days inrats.51. Mating systems There are two types of mating systems: monogamous—where onemale is paired with one female, and polygamous—where severalfemales are housed in a cage with one or more males. Monogamousmating provides ease of recordkeeping and maximizes opportunitiesfor postpartum breeding. This method requires maintenance of largenumbers of males and has a lower productivity than polygamousmating. Monogamous mating is commonly used for inbred strains andless commonly for outbred stocks. Polygamous mating systems areused primarily for production of outbred stocks.52. Breeding systems There are three major types of breeding systems:∞ inbreeding—to produce inbred strains,∞ outbreeding—to produce outbred stocks,∞ selective breeding—choosing breeding partners based uponspecific physical, behavioral, or physiological parameters.