Effect of wild type Escherichia coli W3110 or Escherichia coli nir-Ptac on methane emission and nitrate toxicity in nitrate-treated sheep

Abstract

The effects of the two kinds of Escherichia coli ( E. coli) strains, the wild type E. coli W3110 or E. coli nir-Ptac, which has enhanced nitrite reduction activity, on methane (CH 4) emission and nitrate toxicity in nitrate-treated sheep were assessed in an open circuit respiratory system according to a 4 × 6 Youden square design. Nitrate (1.3 g NaNO 3/kg BW 0.75) and/or E. coli strains were given into the rumen through a fistula as a single dose 30 min after the morning meal. E. coli W3110 or E. coli nir-Ptac cells inoculated for sheep was 150 ml (2 × 10 10 cells/ml). The six treatments consisted of saline (0.9 g NaCl), wild type E. coli W3110, E. coli nir-Ptac, nitrate, nitrate plus E. coli W3110, and nitrate plus E. coli nir-Ptac. Methane emission from sheep was reduced by the inoculation of E. coli W3110 or E. coli nir-Ptac by 6% ( p > 0.05) or 12% ( p < 0.05), respectively. Nitrate markedly inhibited CH 4 emission from sheep. Compared with sheep given nitrate alone, the inoculation of E. coli W3110 to nitrate-treated sheep abated ruminal and plasma toxic nitrite accumulation and blood methaemoglobin production, while keeping ruminal methanogenesis low. Ruminal and plasma toxic nitrite accumulation and blood methaemoglobin production in sheep were unaffected by the inoculation of E. coli nir-Ptac. These results suggest that ruminal methanogenesis may be reduced by the inoculation of E. coli W3110 or E. coli nir-Ptac. The inoculation of E. coli W3110 may abate nitrate toxicity when nitrate is used to inhibit CH 4 emission from ruminants.