Jilin Inter-Regional Cooperation Centre for the Scientific and Technological Innovation of Ruminant Precision Nutrition and Smart and Ecological Farming, Jilin Agricultural Science and Technology University, 1 Xuefu Road, Zuojia, Jilin 132109, China.
Grasslands Research Centre, AgResearch Limited, Private Bag 11008, Palmerston North 4442, New Zealand.
Animal. 2020 May;14(5):952-962. doi: 10.1017/S1751731119002799. Epub 2019 Nov 18.
Low methane (CH4) emissions from sheep fed forage rape (Brassica napus) might be related to low ruminal pH value. In this study, sodium carbonate (Na2CO3: SC) was supplemented to the diet to alter ruminal pH for evaluation of its role in CH4 emissions from sheep fed forage rape. Fourteen intact and eight fistulated Romney sheep were adapted to forage rape over 32 days and then randomly allocated to one of two groups: diets supplemented with SC or not (control). Methane emissions were measured from intact sheep in seven experimental periods. In parallel, ruminal pH and fermentation characteristics were assessed using the fistulated sheep. In the first (P01) and the second (P02) periods, none of the sheep received SC to examine the baseline CH4 emissions. The P01 period was used as a covariate for analysis of gas emission measurements in subsequent measurement periods. Sodium carbonate was offered at 5% of the forage DM in P03 and P04, increased to 8% in P05 and P06 to assess the effect of pH increase on CH4 emissions and stopped in P07 to assess if the CH4 emissions reverted to values similar to those measured before the supplementation started. Methane yield (g/kg forage DM intake) was similar for the sheep in both groups during P02 and P03, but sheep supplemented with SC in the diet emitted 36%, 49% and 30% more CH4 per unit of forage DM intake than those in the control group during P04, P05 and P06, respectively. Emissions returned to similar levels when SC supplementation was ceased in P07. Ruminal pH was 0.412 to 0.565 units higher in SC supplemented sheep than for the control group during the SC treatment periods. Based on the lack of an immediate response in CH4 emissions to the supplementation of SC in P03, the positive responses in P04 to P06 and the rapid disappearance of the response after supplementation with SC stopped in P07, we propose a new hypothesis that ruminal pH effects on CH4 emissions are possibly through medium-term changes in microbial and methanogenic communities in the rumen, rather than a direct, short-term impact on methanogens per se. In conclusion, SC supplemented to the forage rape diet of sheep increased rumen pH, leading to an increase in CH4 emissions. Low ruminal pH in sheep fed forage rape explains, at least partially, the reported low CH4 emissions from sheep fed with this forage crop.
绵羊采食油菜饲粮时甲烷（CH4）排放量低可能与瘤胃 pH 值低有关。本研究中，添加碳酸钠（Na2CO3：SC）来改变瘤胃 pH 值，以评估其在绵羊采食油菜饲粮时对 CH4 排放的作用。14 只完整绵羊和 8 只去势绵羊经过 32 天适应油菜饲粮后，随机分为两组：添加或不添加 SC 的饲粮（对照组）。7 个实验期内对完整绵羊进行甲烷排放测量。同时，利用去势绵羊评估瘤胃 pH 值和发酵特性。在第 1 期（P01）和第 2 期（P02），两组绵羊均不添加 SC 以检测基础 CH4 排放量。P01 期被用作分析后续测量期气体排放测量的协变量。P03 和 P04 期向饲粮中添加 5%的油菜饲粮 DM 中的 SC，P05 和 P06 期增至 8%，以评估 pH 值升高对 CH4 排放的影响，并在 P07 期停止添加 SC 以评估 CH4 排放是否恢复到添加前相似的水平。P02 和 P03 期，两组绵羊的采食油菜饲粮的甲烷产量（g/kg 干物质采食量）相似，但 P04、P05 和 P06 期，添加 SC 的绵羊每单位油菜饲粮干物质采食量比对照组多排放 36%、49%和 30%的 CH4。当 P07 期停止添加 SC 时，排放恢复到相似水平。添加 SC 期间，绵羊的瘤胃 pH 值比对照组高 0.412 至 0.565 个单位。根据 P03 期添加 SC 对 CH4 排放无即时响应、P04 期至 P06 期的阳性响应以及 P07 期停止添加 SC 后响应迅速消失，我们提出了一个新的假设，即瘤胃 pH 值对 CH4 排放的影响可能是通过瘤胃微生物和产甲烷菌群落的中期变化，而不是直接对产甲烷菌本身产生短期影响。总之，添加 SC 会增加绵羊采食油菜饲粮的瘤胃 pH 值，导致 CH4 排放增加。绵羊采食油菜饲粮时低瘤胃 pH 值至少部分解释了报道中绵羊采食该饲粮时低 CH4 排放的原因。
