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Nutritional control to reduce environmental impacts of intensive dairy cattle systems

机译：营养控制减少密集乳制牛系统的环境影响

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Demand for milk and meat is expected to increase rapidly. In the absence of major corrective measures, the environmental impact of cattle production will worsen. In this review, dairy cattle nutrient flows and nutrient accumulation are described by looking at nitrogen (N), phosphorus (P) and methane (CH4) emissions and mitigation options to limit or minimize nutrient loading in the environment. The efficiency of conversion of feed N into milk N is highly variable. Almost all the avoidable N losses is excreted in urine, which is of particular concern with respect to environmental impact. A rational reduction in N intake per cow, with minimal negative effects on lactating performance, will decrease urinary N excretion. This requires a proper balance between energy and N sources at rumen and post-rumen level. At the rumen level, reducing the N to energy ratio or reducing protein degradation rate are promising options. Splanchnic tissues have a high metabolic activity and remove a variable part of the amino acids available for absorption. However, quantitative knowledge on post-rumen N metabolism is limiting, and current protein evaluation systems appear unable to support decision making with a view to reduce N losses. Surplus P is largely excreted in faeces. The variation in efficiency of conversion of feed P into milk P is considerable. Current recommended dietary P concentrations have a large safety margin and reductions in P intake are possible without detrimental effects on animal production and health. Similar to N efficiency, P efficiency of the cow improves when more energy dense diets are fed. Several nutritional strategies have been proposed to reduce CH4 emissions. Among these, shifting from sugars towards starch in the diet, shifting from cell wall material towards starch, or feeding starch sources more resistant to rumen degradation all lead to substantial reductions in CH4 production per unit of rumen digested substrate. Although a number of feed additives have been shown to decrease CH4 production in vitro effectively, data on long-term in vivo effects are scarce. Variation at animal level in losses of N, P and CH4 is considerable. Proper integration of the various subsystems (soil, plant, animal) into a whole farm model requires appreciation of animal variation. Results from current farm system evaluations appear unsatisfactory in this respect. Finally, much more consideration of the interactions between losses of N, P and CH4 is required. In particular, nutritional management to reduce N losses has variable effects on methane emissions of dairy cattle.
机译：预计对牛奶和肉的需求将迅速增加。在没有重大的纠正措施的情况下，牛产量的环境影响将恶化。在本文中，通过查看氮气（n），磷（p）和甲烷（Ch 4）排放和缓解方案来限制或最大限度地减少环境中的营养负荷来描述乳制品养牛营养流和营养积累。进料N-进牛奶N的效率是高度变化的。几乎所有可避免的N损失都在尿液中排出，这对环境影响特别关注。每牛的N摄入量的合理降低，对哺乳期性能的负面影响最小，将降低尿液N排泄。这需要在瘤胃和瘤胃后水平的能量和N来源之间进行适当的平衡。在瘤胃水平，减少N至能量比或降低蛋白质降解率是有前途的选择。 Splanchnc组织具有高代谢活性，并除去可用于吸收的氨基酸的可变部分。然而，对瘤胃后N代谢的定量知识是限制性的，并且目前的蛋白质评估系统似乎无法支持决策，以减少N损失。剩余P在粪便中大大排泄。进料P转化为牛奶P的效率的变化很大。目前推荐的膳食P浓度具有很大的安全保证金，并且P摄入量的降低也是可能对动物生产和健康的不利影响。与N效率相似，母牛的P效率可以提高，当喂食更多的能量密集的饮食时。已经提出了几种营养策略来减少CH4排放。其中，从饮食中从糖转移到淀粉中，从细胞壁材料转移到淀粉，或者喂养更耐瘤胃降解的淀粉源，所有导致每单位瘤胃消化底物的CH 4产生的显着降低。尽管已经证明了许多饲料添加剂可以有效地减少CH4生产，但长期效应的长期数据是稀缺的。 N，P和CH4损失中动物水平的变化很大。适当整合各个子系统（土壤，植物，动物）进入整个农场模型需要升值动物变异。目前农场系统评估的结果在这方面看起来不令人满意。最后，需要更多地考虑N，P和CH4的损失之间的相互作用。特别是，减少N损失的营养管理对奶牛的甲烷排放产生了可变影响。

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