Technical Abstract: Sulfate reducing bacteria (SRB) in swine manure storage pit (SMSP) slurries are responsible for the production of hydrogen sulfide emitted from livestock facilities. However, little is known about the prevalence and diversity of SRB in livestock wastes. In this study, SRB populations in SMSP slurries were identified and quantified through sequence analysis and quantitative, real-time PCR (QRT-PCR) analysis of the dissimilatory sulfite reductase (dsr) gene. Cloned dsrAB gene sequences from SMSP slurry were less than 85% similar to sequences in the databases. However, dsrAB sequences of isolates from SMSP SRB enrichment cultures were over 95% similar to Desulfovibrio desulfuricans. QRT-PCR assays were developed to target the three main groups of SRB. The concentration of Desulfobulbus-like (2.2 X 104 to 1.6 X 108 dsrA copies mL-1 slurry), Desulfovibrio-like (3.3 X 103 to 1.0 X 106 dsrA copies mL-1 slurry), and Desulfovibrio desulfuricans (3.2 X 104 to 5.5 X 106 dsrA copies mL-1 slurry) SRB varied according to time of year, individual house, and depth of slurry. Based on these numbers, SRB averaged around 1% of the total microbial population in the SMSP. These results suggest that the SRB in SMSP slurries possess novel dsr genes and their concentrations are highly variable.