Suppressed murine mammary tumor virus (MuMTV) expression in RIII female mice treated neonatally with goat antiserum to MuMTV.

Passive immunization of newborn inbred RIII (R3) mice with the globulin fraction of goat antiserum to murine mammary tumor virus (MuMTV) successfully suppressed MuMTV expression in the milk of some of the treated mice throughout nine successive lactations. No mammary tumors developed in the MuMTV-suppressed mice during the first 9 months, whereas all untreated R3 female breeders expressed MuMTV in the milk of the third lactation, and all developed tumors before 9 months of age (mode and median: 189 days).