基于挥发性脂肪酸化学计量模型体外预测山羊瘤胃甲烷产量的精度

Accuracy of predicting in vitro ruminal methane production in goats using volatile fatty acids stoichiometric models

利用挥发性脂肪酸(VFA)的化学计量模型[CH4=0.5Ace-0.25Pro+0.5But-0.25Val,模型1,式中,CH4、Ace、Pro、But和Val分别表示甲烷、乙酸、丙酸、丁酸和戊酸的产量]预测瘤胃甲烷产量的精度.选用常见的10种化学成分差异显著的饲料原料(包括4种精饲料和6种粗饲料)进行体外模拟反刍家畜瘤胃发酵试验,测定发酵72 h后的VFA组成和CH4产量.利用模型精度分析方法比较CH4产量预测值与实测值间的差异.结果表明:模型1估算的CH4生成量普遍高于实测值,其偏差、斜率和随机误差分别为62.6%、11.7%和25.7%,固定误差>70%.考虑到VFA代谢生成氢的80%用于合成CH4,VFA化学计量模型表达为模型2[CH4=0.8(0.5Ace-0.25Pro+0.5But-0.25Val)].与模型1相比(均方预测误差=0.60),模型2的预测精度大大提升(均方预测误差=0.18),模型2的偏差、斜率和随机误差分别为2.1%、5.7%和92.3%,固定误差<10%.模型1认为VFA生成过程所产生的氢全部被甲烷菌用于合成CH4,没有考虑氢代谢的其他途径,这是导致预测值大于实测值的一个重要原因.

This study was conducted to investigate the accuracy of predicting in vitro ruminal methane （ CH4 ） production using volatile fatty acids （VFA） stoichiometric models [ CH4 = 0. 5Ace- 0.25Pro＋0. 5But-0. 25Val] （model 1 ）, where CH4, Ace, Pro, But and Val are the production amounts of CH4, acetate, propionate, butyrate and valerate, respectively. Ten common feedstuffs, including four concentrates and six roughages with a wide range of chemical composition were incubated in serum bottles, and VFAs and CH4 production at 72 h were determined. The differences between the predicted and measured CH4 production were quantified using the model accuracy analysis. The results showed that the predicted CH4 production amounts were generally greater than the measured values obtained using the model 1, and the bias, slope and random error were 62.6% , 11.7% and 25.7%, respectively, indicating that fixed error exceeded 70%. By assuming 80% of total hydrogen being used for CH4 synthesis, the VFA stoichiometric model could be re-expressed as [ CH4 =0.8（0.5Ace-0. 25Pro＋0. 5But-0. 25Val） ] （model 2）. The root mean square prediction error （rMSPE = 0.18） for model 2 was less than for model 1 （rMSPE = 0.60）. In addition, the bias, slope and random error of the model 2 were 2.1%, 5.7%, 92.3%, respectively, indicatingthat fixed error was less than 10%. In model 1, hydrogen formation resulting from VFA production were assumed to be totally consumed by methanogens for CH4 synthesis, without considering other pathways of hydrogen metabolism, which was the main factor resulting in the higher predicted values than the measured values.