A Tier 3 Method for Enteric Methane in Dairy Cows Applied for Fecal N Digestibility in the Ammonia Inventory
A Tier 3 Method for Enteric Methane in Dairy Cows Applied for Fecal N Digestibility in the Ammonia Inventory
复制标题
DOI：
10.3389/fsufs.2018.00066
复制
发表时间：
2018-11-05
影响因子：
4.7
通讯作者：
Sebek, Leon B. J.
中科院分区：
文献类型：
--
作者：
Bannink, Andre;Spek, Wouter J.;Sebek, Leon B. J.
目前牛排泄物中的氮排放清单依赖于荷兰饲养表中粪便氮消化率数据，假设膳食成分可添加以获得膳食值（CVB 模型）。或者，粪便氮消化率可以通过胃肠道消化的动态机械模型来估计，该模型目前在荷兰用作肠道甲烷预测的第三层（第三层模型）。用作方法 3 模型输入的淀粉、中性洗涤纤维 (NDF) 和粗蛋白的原位瘤胃降解特性的估计基于荷兰饲养表（蛋白质评估系统）。这两种方法都在粪便氮消化率的独立数据集上进行了评估，该数据集是根据自 1999 年以来发表的关于奶牛氮平衡数据的同行评审论文构建的（54 项试验，242 种处理方法）。结果表明，与 Tier 3 模型 (69.8 +/- 4.52%) 相比，观察到的表观粪便氮消化率 (67.0 +/- 6.77%) 被系统性地高估，特别是 CVB 模型 (73.8 +/- 4.35%)。对于仅包含荷兰试验观察结果的数据集，观察到的粪便氮消化率 (70.4 +/- 7.33%) 也被 CVB 模型 (76.4 +/- 5.27%) 系统性地高估，但 Tier 3 模型 (69.7 +/- 5.81%) 则没有。以研究为随机因子的混合模型分析表明，观察到的粪便氮消化率与预测的粪便氮消化率之间的回归斜率小于 1，特别是对于 CVB 模型（CVB 模型斜率在 0.405 和 0.560 之间变化，而第 3 层模型斜率在 0.418 和 0.657 之间变化）。 CVB 模型对消化率 6-7% 单位的过度预测将导致氨库存中氨氮排泄（尿氮）的过度预测，以及对营养措施氮缓解潜力的估计存在偏差。本研究证明了与 CVB 模型相比，使用第 3 层模型预测粪便氮表观消化率平均水平的优势。作为第 3 层模型输入的淀粉、NDF 和粗蛋白原位瘤胃降解特性的一般估计似乎适用于荷兰试验，但不适用于非荷兰试验。
The current inventory of N emission from cow excreta relies on fecal N digestibility data in Dutch feeding tables, assuming additivity of dietary ingredients to obtain diet values (CVB model). Alternatively, fecal N digestibility can be estimated by a dynamic, mechanistic model of digestion in the gastrointestinal tract, currently used as Tier 3 for enteric methane prediction in the Netherlands (Tier 3 model). Estimates of in situ rumen degradation characteristics for starch, neutral detergent fiber (NDF) and crude protein used as an input for the Tier 3 model were based on Dutch feeding tables (the protein evaluation system). Both methods were evaluated on independent dataset on fecal N digestibility that was constructed from peer-reviewed papers on N balance data for dairy cows published since 1999 (54 trials, 242 treatment means). Results indicate that observed apparent fecal N digestibility (67.0 +/- 6.77%) was systematically over-predicted in particular by the CVB model (73.8 +/- 4.35%) compared to the Tier 3 model (69.8 +/- 4.52%). For the dataset including only observations from Dutch trials the observed fecal N digestibility (70.4 +/- 7.33%) was also systematically over-predicted by the CVB model (76.4 +/- 5.27%) but not by the Tier 3 model (69.7 +/- 5.81%). Mixed model analysis with study as random factor indicated the slope of the regression between observed and predicted fecal N digestibility to be smaller than 1, in particular for the CVB model (CVB model slope varied between 0.405 and 0.560 and Tier 3 model slope between 0.418 and 0.657). The over-prediction by the CVB model with 6-7%-units of digestibility will lead to an over-predicted ammoniacal N excretion (urinary N) in the ammonia inventory, and biased estimation of N mitigating potential of nutritional measures. The present study demonstrates the benefit of using the Tier 3model to predict the average level of apparent fecal N digestibility compared to the CVB model. The general estimates of in situ rumen degradation characteristics for starch, NDF and crude protein used as input for the Tier 3 model seemed applicable for the Dutch trials but less so for the non-Dutch trials.