Murine astrovirus (MuAstV) is a recently identified, widespread infection among laboratory mice. Our goal was to determine the duration of MuAstV infection, susceptibility of pups, and efficacy of soiled-bedding sentinels and environmental monitoring. Eight CD1 dams and their litters of 3-d-old pups and 8 CD1 dams and their litters of 13-d-old mice were inoculated orally with MuAstV. Neither dams nor offspring demonstrated any clinical signs, and MuAstV had little to no effect on weight gain in pups. MuAstV RNA was detected in feces from 15 of the 16 dams through postnatal day (PND) 21, and 9 dams were still shedding MuAstV at PND 42. MuAstV RNA was highest in intestines of mice. Low levels of MuAstV RNA were sporadically detected in the spleen, liver, and kidney. MuAstV was detected in 97% of feces from 3- to 9-wk-old mice born to infected dams. Several weanlings became pregnant, and intestines from their pups were MuAstV-negative at PND 0 through 5. Weekly swabs of cages housing MuAstV-infected mice were MuAstV-positive through PND 42. Swabs of the rear exhaust manifold of the ventilated rack were MuAstV-positive at 21 through 56 d after inoculation. In addition, 98% of sentinels that received soiled bedding from dams and their litters and 83% of sentinels that received soiled bedding from weaned mice were MuAstV-positive. Feces from most sentinels exposed to soiled bedding that had been stored for 1, 2 or 3 wk before addition of the sentinels were MuAstV-positive.