The effect of high-sugar grass on predicted nitrogen excretion and milk yield simulated using a dynamic model
The effect of high-sugar grass on predicted nitrogen excretion and milk yield simulated using a dynamic model
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DOI：
10.3168/jds.2010-4059
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发表时间：
2011-06-01
影响因子：
3.5
通讯作者：
France, J.
中科院分区：
文献类型：
--
作者：
Ellis, J. L.;Dijkstra, J.;France, J.
高糖草品种因其减少牛的氮（N）排泄和增加产奶量的潜力而受到相当大的关注。然而，在公布的结果中，反应的程度存在相当大的差异。本研究的目的是解释变化的响应，使用动态机理模型来预测观察到的N和牛奶产量的结果，从文献中，并从模拟数据。研究的影响是（1）水溶性碳水化合物[WSC; g/kg干物质（DM）]增加;（2）随着WSC增加植物的粗蛋白（CP）和中性洗涤纤维（NDF）含量的变化;和（3）氮肥水平。用于评价模型N和产奶量预测的数据库由4项已发表的研究组成，其中28项治疗方法正在评价高糖草。水溶性碳水化合物的含量范围为95至248克/公斤的DM，CP含量范围为115至263克/公斤的DM，和NDF含量范围为400至568克/公斤的DM。尿N，牛奶N，总N排泄预测模型，并遵循每个研究中观察值的方向模式。模拟结果表明，氮的利用率随着饲料中WSC含量的增加而增加，但不同程度上取决于所研究的草情景。在氮利用率和尿氮水平方面的最大效益被认为是当WSC含量的草增加，以牺牲CP，其次是50：50 CF和NDF的组合，其次是NDF的贸易。模拟产奶量略有下降时，WSC增加CP的费用，略有增加时，它增加了CP和NDF的混合物的费用，并增加了最WSC增加时，NDF的费用。结果略有放大的条件下，低氮施肥和粮食喂养的情况下。总的来说，建模作为一种解释性工具是有用的。与文献中高WSC牧草饲喂结果的差异可能至少部分是WSC水平（g/kg DM）增加、植物CP和NDF组分中同时发生的变化以及饮食营养水平（谷物饲喂和氮肥水平）的结果。
High-sugar grass varieties have received considerable attention for their potential to reduce nitrogen (N) excretion and increase milk yield in cattle. However, considerable variation exists in the magnitude of response in published results. The purpose of this study is to explain the variation in response using a dynamic mechanistic model to predict observed N and milk yield results from the literature, and from simulated data. Examined effects were (1) water-soluble carbohydrate [WSC; g/kg of dry matter (DM)] increase; (2) change in crude protein (CP) and neutral detergent fiber (NDF) content of the plant with WSC increase; and (3) the level of N fertilization. The database for evaluation of model N and milk yield predictions consisted of 4 published studies with 28 treatment means for which high-sugar grasses were being evaluated. Water-soluble carbohydrate content of the diets ranged from 95 to 248 g/kg of DM, CP content ranged from 115 to 263 g/kg of DM, and the NDF content ranged from 400 to 568 g/kg of DM. Urine N, milk N, and total N excretion were predicted well by the model and followed the directional pattern of observed values within each study. Simulation results showed that the N utilization ratio increased as the WSC content of the diet increased, but to varying degrees depending on the grass scenario examined. The greatest benefit in terms of N utilization ratio and urine N levels were seen when the WSC content of grass increased at the expense of CP, followed by a 50:50 CF and NDF mix, followed by a trade for NDF. Simulated milk yield decreased slightly when WSC increased at the expense of CP, increased slightly when it increased at the expense of a CP and NDF mix, and increased most when WSC increased at the expense of NDF. Results were amplified slightly under conditions of low-N fertilization and in the absence of grain feeding. Overall, modeling is useful as an explanatory tool. The variation from results in the literature with high-WSC grass feeding may be, at least in part, the result of the level of WSC (g/kg of DM) increase, concurrent changes occurring within the CP and NDF fractions of the plant, and the plane of nutrition of the diet (grain feeding and N fertilization levels).