Hünerberg M, McGinn S M, Beauchemin K A, Entz T, Okine E K, Harstad O M, McAllister T A
J Anim Sci. 2015 Apr;93(4):1760-6. doi: 10.2527/jas.2014-8469.
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.
本研究的目的是确定瘤胃pH值对肉牛甲烷（CH4）排放的影响。在2个试验中，给16头小母牛饲喂高粗饲料（55%大麦青贮料）或高谷物（92%精料；干物质基础）日粮，从而得出瘤胃pH值和CH4数据。两个试验均设计为重复的4×4拉丁方，有4个周期和4种日粮处理。使用开路呼吸室连续4天测量甲烷，每个呼吸室容纳2头小母牛。使用植入式pH记录仪测量个体小母牛的瘤胃pH值。每个呼吸室中2头小母牛的平均瘤胃pH值和CH4排放（克/小时）按30分钟时间段进行汇总。尽管在体外瘤胃产甲烷菌被描述为在pH值<6.0时受到抑制，但在体内，当瘤胃pH值降至亚急性（5.2≤pH<5.5）或急性瘤胃酸中毒（pH<5.2）的阈值水平时，CH4产生率（克/小时）并未降低（P>0.05）。每日平均CH4排放量（克/天）与瘤胃pH值仅呈轻度相关（r2 = 0.27；P<0.05），这表明与高粗饲料日粮相比，高谷物日粮喂养的牛CH4排放较低是由其他因素造成的，如丙酸生成增加或通过速度加快。因此，仅降低瘤胃pH值并不是一种有效的CH4减排策略。使产甲烷菌在瘤胃低pH值情况下存活的机制可能包括群落结构向更耐pH值的菌株转变，或隔离到生物膜或原生动物内的微环境中，在那里产甲烷菌受到保护而免受低pH值影响。
