Strategies for optimizing nitrogen use by ruminants
Strategies for optimizing nitrogen use by ruminants
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DOI：
10.1017/s1751731110000911
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发表时间：
2010-07-01
期刊：
影响因子：
3.6
通讯作者：
van Vuuren, A. M.
中科院分区：
文献类型：
--
作者：
Calsamiglia, S.;Ferret, A.;van Vuuren, A. M.
与其他生产动物的较高效率相比，反刍动物的氮利用效率通常较低（约 25%）且变化很大（10% 至 40%）。低效率会对生产性能和环境产生影响。为了提高反刍动物的氮利用效率，人们付出了很多努力，虽然我们对氮需求和代谢的理解已经取得了重大进展，但总体效率仍然很低。一般来说，氮利用效率的最大化只能以生产性能的一些损失为代价。然而，通过了解氮代谢控制中涉及的关键机制，可以实现最佳的生产和氮利用。瘤胃中的关键因素包括瘤胃中氮捕获的效率（每克瘤胃可用氮的细菌氮克数）和蛋白质降解的改变。传统上，蛋白质降解是通过改变饲料（物理和化学处理）来调节的。改变参与肽降解和氨基酸脱氨的瘤胃微生物菌群提供了一种需要解决的替代方法。目前的证据表明，在典型的饲养条件下，进入瘤胃的氮净循环有限（血液尿素氮吸收减去氨氮吸收），但了解控制尿素跨瘤胃壁运输的因素可能会扭转平衡，以利用反刍动物的循环能力。最后，门引流内脏 (PDV) 和肝脏中存在大量的氨基酸 (AA) 代谢。然而，这一过程大部分是通过从动脉血中摄取 AA 发生的，而不是在“吸收”过程中发生的。因此，AA 在被 PDV 和肝脏使用之前先进入外周循环和乳腺。在这些情况下，乳腺在决定氮利用效率方面起着关键作用，因为 PDV 和肝脏将使用超过乳腺所需的 AA。乳腺中的蛋白质合成似乎受到局部和全身信号的严格调节。了解乳腺中调节 AA 供应和吸收的因素以及乳蛋白的合成，应有助于制定日粮，增加乳腺对 AA 的总吸收，从而减少 PDV 和肝脏对 AA 的利用。更好地了解这些关键过程，应有助于制定提高反刍动物氮利用效率的策略。
The efficiency of N utilization in ruminants is typically low (around 25%) and highly variable (10% to 40%) compared with the higher efficiency of other production animals. The low efficiency has implications for the production performance and environment. Many efforts have been devoted to improving the efficiency of N utilization in ruminants, and while major improvements in our understanding of N requirements and metabolism have been achieved, the overall efficiency remains low In general, maximal efficiency of N utilization will only occur at the expense of some losses in production performance. However, optimal production and N utilization may be achieved through the understanding of the key mechanisms involved in the control of N metabolism. Key factors in the rumen include the efficiency of N capture in the rumen (grams of bacterial N per grams of rumen available N) and the modification of protein degradation. Traditionally, protein degradation has been modulated by modifying the feed (physical and chemical treatments). Modifying the rumen micro flora involved in peptide degradation and amino acid deamination offers an alternative approach that needs to be addressed. Current evidence indicates that in typical feeding conditions there is limited net recycling of N into the rumen (blood urea-N uptake minus ammonia-N absorption), but understanding the factors controlling urea transport across the rumen wall may reverse the balance to take advantage of the recycling capabilities of ruminants. Finally, there is considerable metabolism of amino acids (AA) in the portal-drained viscera (PDV) and liver However, most of this process occurs through the uptake of AA from the arterial blood and not during the 'absorptive' process. Therefore, AA are available to the peripheral circulation and to the mammary gland before being used by PDV and the liver In these conditions, the mammary gland plays a key role in determining the efficiency of N utilization because the PDV and liver will use AA in excess of those required by the mammary gland. Protein synthesis in the mammary gland appears to be tightly regulated by local and systemic signals. The understanding of factors regulating AA supply and absorption in the mammary gland, and the synthesis of milk protein should allow the formulation of diets that increase total AA uptake by the mammary gland and thus reduce AA utilization by PDV and the liver A better understanding of these key processes should allow the development of strategies to improve the efficiency of N utilization in ruminants.