Two mouse strains (SHN and SLN) with high and low incidences, respectively, of mammary tumors were established from the same basal stock of Swiss albino mice that were unrelated in origin to other mouse strains with mammary tumors. In the breeders, mammary tumor incidence and average age of the mice when they developed mammary tumors were 97.2% and 6.6 months for SHN, and 55.7% and 10.1 months for SLN, respectively. In virgins, tumor incidence and age at development of tumors were 88.3% and 8.7 months for SHN, and 9.7% and 14.4 months for SLN, respectively. In SLN mice, the efficiency of selection was more marked in virgins than in breeders. The number of mammary tumors per mouse was significantly higher in SHN than in SLN. SHN females were superior to SLN females in normal and preneoplastic mammary growth, reproductivity, lactation performance, mammary sensitivity to pituitary mammotropin, and activity of mammary tumor virus. Selection had little effect on the pituitary prolactin secretion.
No takes yet. Share an insight, caveat, or question.
Nagasawa et al. (1976) studied this question.