SURVIVAL OF FECAL BACTERIA IN DAIRY Cow MANURE

摘要

Bacterial pollution of water is impacted to a great extent by the ability of bacteria to survive in manure following excretion. We investigated the effects of environmental temperature (4℃, 27℃, and 41℃) and manure moisture content (30%, 55%, and 83%) on the survival and release of indicator bacteria in dairy cow manure. Fresh manure samples of about 60 g were packed to 12 mm depth in polystyrene dishes and held at controlled temperatures and moisture contents for up to 103 days. Supernatant from a distilled-water extraction was enumerated for fecal bacteria (fecal coliforms, Escherichia coli, and fecal streptococci) by the membrane filtration method. Bacterial populations increased as much as 2.5 log10 (over 300X) in the three days following excretion. Temperature had a significant overall effect on survival of all three fecal bacteria, whereas moisture content produced a consistent effect on fecal streptococci survival only. Fecal streptococci showed no significant die-off at any temperature or moisture content studied. In contrast, no measurable E. coli or fecal coliforms were found in supernatant water samples from the 41℃ treatment after day 35. E. coli and fecal coliform populations for the 4℃ treatment at lower moisture content (30% and 55%) conditions were close to the detection limits after five weeks, but significant numbers of E. coli (2.34 × 10{sup}4 cfu g{sup}(-1) wet manure) and fecal coliforms (3.84 × 10{sup}4 cfu g{sup}(-1) wet manure) remained for the 4℃ treatment at 83% moisture content after 103 days. First-order die-off rate coefficients for E. coli were found to be appropriate after day 3 for about a 3-week period and averaged 0.11 d{sup}(-1) at 4℃, 0.20 d{sup}(-1) at 27℃, and 0.32 d{sup}(-1) at 41℃. Results from this study suggest that barnyard, feedlot, and manure management practices that detain manure at higher temperatures (e.g., 41℃) will decrease the E. coli and fecal coliform populations but not those of fecal streptococci. Coliform bacterial populations tested remained viable for long periods (>3 months) particularly at moderate temperature (27℃) for any moisture level, and streptococci survived under all conditions studied.