title: Impact of ruminal pH on enteric methane emissions.
abstract: The objective of this study was to determine the impact of ruminal pH on methane (CH4) emission from beef cattle. Ruminal pH and CH4 data were generated in 2 experiments using 16 beef heifers offered high-forage (55% barley silage) or high-grain (92% concentrate; DM basis) diets. Both experiments were designed as a replicated 4 × 4 Latin square with 4 periods and 4 dietary treatments. Methane was measured over 4 consecutive days using open-circuit respiratory chambers with each chamber housing 2 heifers. The ruminal pH of individual heifers was measured using indwelling pH loggers. The mean ruminal pH and CH4 emission (g/h) of 2 heifers in every chamber were summarized in 30-min blocks. Even though rumen methanogens have been described to be inhibited by a pH < 6.0 in vitro, in vivo CH4-production rates (g/h) did not decrease when ruminal pH declined to threshold levels for subacute (5.2 ≤ pH < 5.5) or acute ruminal acidosis (pH < 5.2; P > 0.05). Daily mean CH4 emission (g/d) and ruminal pH were only mildly correlated (r2 = 0.27; P < 0.05), suggesting that additional factors, such as increased propionate formation or passage rate, account for the lower CH4 emissions from cattle fed high-grain as compared to high-forage diets. Lowering ruminal pH alone is, therefore, not an effective CH4-mitigation strategy. Mechanisms permitting methanogens to survive episodes of low-ruminal pH might include changes in community structure toward more pH-tolerant strains or sequestration into microenvironments within biofilms or protozoa where methanogens are protected from low pH.
authors.forename: M
authors.initials: M
authors.lastname: Hünerberg
authors.forename: S M
authors.initials: SM
authors.lastname: McGinn
authors.forename: K A
authors.initials: KA
authors.lastname: Beauchemin
authors.forename: T
authors.initials: T
authors.lastname: Entz
authors.forename: E K
authors.initials: EK
authors.lastname: Okine
authors.forename: O M
authors.initials: OM
authors.lastname: Harstad
authors.forename: T A
authors.initials: TA
authors.lastname: McAllister
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D002523:Edible Grain; D005260:Female; D001467:Hordeum; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000378:metabolism*; D012417:Rumen / Q000378:metabolism*; D012820:Silage
chemical_list: D008697:Methane