Another note on inbred laboratory mouse strains. None of them have as long of an average life-span as out-bred mice. And, to create an inbred strain, a number of out-bred mice are selected originally, then bred brother to sister for generations. A fair number of brother sister pairs have to be selected initially, because many of the attempts fail, typically becoming extinct at between 5 and 10 generations of inbreeding.

    Here is some of the health information on three commonly used laboratory mouse strains as compiled by Michael Festing in a reference book on inbred laboratory mouse strains.

CBA, widely distributed general use strain, originally selected for low mammary tumor incidence. Life span short to intermediate. High gross tumor incidence 29% in males, 55% in females (includes lymphomas, hepatomas (liver cancer), lung adenomas, and yes mammary tumors). High systolic blood pressure. Resistant to Salmonella typhimarium, highly susceptable to measles. Breeding performance varies according to subline, from good to poor.

C3H, among the most widely used of all mouse strains. Has retinal degeneration. Extremely susceptable to a virally induced mammary tumor type. Almost 100% of unfostered females get mammary adenocarcinomas, this is not seen in SPF (specific pathogen free) colonies. In otherwords the female mouse pups must be given to another mother from a different mouse strain to survive, unless they are from lines thatare kept in a virus and bacteria free sterile environment. Otherwise intermediate life-span. 9-23% liver tumors, 2-10% lung tumors, 21-36% non-virally induced mammary tumors, 13-26% heart defects, 13-26% cystic ovaries. Susceptable to various carcinogens. Resistant to Salmonella typherium and mouse hepatitus virus. Susceptable to Entamoeba marinum, highly susceptable to mammary tumor virus. Breeding performance intermediate to good.

C57BL, easily the most widely used strain, used as the genetic background for a large number of congenic strains. A relatively inquisitive and intellegent strain of inbred mice. Intermediate to longlife-span. Small kidney/body weight ratio. Hyperphalangy and polydactyly (extra foot and toe bones) occur at low incidence, hydrocephalus 4.1%. High thyroid activity. Resistant to many carcinogens except estrogens, which produces a high frequency of pituitary tumors. Some substrains have a high incidence of amyloidosis. High susceptability to one leukemia virus, susceptable to Salmonella typhimurium. Resistant to Herpes simplex. Variable breeding performance depending on substrain.