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B oth feces and urine are vehicles for sulfur excretion. Three forms of sulfur, inorganic sulfate (principal), etheral (ether origin) sulfur, and neutral sulfur, are found in urine (Maynard and Loosli, 1969). Fecal sulfur is of endogenous (plant) origin (Fontenot and Church, 1979).

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PORCINE reproductive and respiratory syndrome virus (PRRSV) is an enveloped RNA virus that is both heat and pH labile. It is readily inactivated by drying or following contact with a broad range of disinfectants (Benfield and others 1992, Bloemraad and others 1994). In addition, PRRSV survives for extended periods when frozen or if in a moist environment (Benfield and others 1992, Bloemraad and others 1994, Pirtle and Beran 1996. In a study by Pirtle and Beran (1996), a standard concentration of PRRSV (2 x 10 5 TCID50/ml) was added to a sample of water taken from a well and a sample of city water at a 1:10 dilution and incubated at 25 to 27°C for 11 days. On each day of the incubation period, an aliquot of inoculated liquid from both sources was collected and tested for the presence of PRRSV. Infectious PRRSV was recovered from well water after nine days and from city water after 11 days.For handling swine waste, many commercial production systems use high-volume, underslat flushing systems that recirculate lagoon effluent back to the manure pits beneath the animals. With these systems, animals frequently come into contact with effluent from the lagoon as it splashes upward through the slotted concrete flooring (S. Dee, personal observations). The aims of the present study were to determine how long PRRSV could remain viable in swine effluent and to test the infectivity of PRRSV-inoculated effluent in naive pigs.Effluent was obtained from a single-stage, anaerobic lagoon, with a depth of 6·6 m, that serviced the breeding, gestation, farrowing and nursery facilities of a commercial swine operation located in the mid-west USA. To initiate the study, a 4 litre sample of effluent from the pit of the nursery facility was collected as it flowed into the lagoon basin. Ten 5 ml samples of the effluent were collected and tested for the presence of PRRSV by TaqMan PCR (Perkin-Elmer Applied Biosystems) and virus isolation at the Minnesota Veterinary Diagnostic Laboratory (Bautista and others 1993, Molitor and others 1997). All samples were negative by both tests. Four 20 ml aliquots of effluent were then collected from the original sample, and a 2 ml aliquot of PRRSV strain MN 30-100 (Bierk and others 2001) was added to each one. The concentration of virus present in each 22 ml aliquot of effluent was determined to be 2 x 10 4 TCID50/ml. Two of the four aliquots were held at 4°C and the other two were held at 20°C.For a positive control, a 2 ml aliquot of PRRSV MN 30-100 was added to 20 ml of minimum essential medium (MEM) and incubated at 4°C and 20°C. For a negative control, a shaminoculated effluent (20 ml MEM plus 2 ml effluent) was stored at the same temperatures. At 24-hour intervals on days 1 to 12 after inoculation, a 1 ml sample of each of the four aliquots was collected using separate syringes, and the samples were placed in sterile 3 ml plastic tubes. These samples and the remaining 10 ml of the four PRRSV aliquots were frozen at -70°C.Following the completion of the 12-day sampling period, all samples were test...