疾病是如何影响营养需求的

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疾病是如何影响营养需求的

作者：Ioannis Mavromichalis, Ph.D. 译者：刘彩红

序言：生病的动物吃很少的食物,但是很明显,他们也有不同的营养需求。

    在生病时,从合成代谢到分解代谢的代谢改变被认为是免疫系统应答成功的关键因素,从生长到支持免疫系统功能控制病原感染,营养必须重新组合分布。然而,目前,存在很少专门为生病动物制定加强营养的饲料日粮配方资料。

免疫系统应答

    广泛地认为,暴露于病原体触发了免疫系统,在应答中释放很多前炎症细胞因子,这些因子不仅调节免疫应答,而且调动整体代谢。研究已经清洗地表明免疫系统被这些细胞因子激活后(甚至在亚临床水平),抑制了食欲,减少了肌肉蛋白的合成。同时也减少了肌肉蛋白质的降解。因此,生病动物的代谢状态连通合成代谢(生长)到分解代谢(肌肉损失)。

    当然,当免疫系统激活时,新陈代谢直接指向免疫系统成分的合成。这种情况发生时,这些过程的营养需求与自然生长不同。今天,还是真正缺乏生病动物的营养需求的有意义资料。所有的“标准”营养需求是从传统的剂量调整试验中得到的,这些试验是使用健康饲养猪在接近最佳状态的条件进行的。
氨基酸

     免疫系统有它自己独立的一套氨基酸需求方案,这不同于生长需求。比如说,急性期细胞因子应答时肝脏产生的蛋白质与骨骼肌肌肉蛋白相比有不同的氨基酸组成，急性期蛋白质有高浓度的芳香族氨基酸(苯丙氨酸、酪氨酸和色氨酸)存在，这些是疾病发作时，在肝脏中大量产生。这些实际上表明肌肉过度退化是由于组成肌肉蛋白和急性蛋白的氨基酸功能不同。
    此外，苏氨酸是免疫G蛋白的主要组成，日粮成分中为猪抗体生产所需的苏氨酸是高于自然生长的需求。除此之外，免疫应激导致氨基酸的持续需求如同氨基酸总需求一起增加。总而言之，抵抗疾病的猪，氨基酸需求可能会增加，然而，赖氨酸需求相对来说低点。

矿物质

     提到矿物质，锌减少免疫竞争，增加感染的机会，这是众所周知的。然而，高浓度锌也可能会影响感染猪的免疫应答，这是由于它可能会干扰正常免疫功能。事实上，很长一段时间，氧化锌的药理剂量常常与性能缺陷相关。
    此外，因为感染期大多数病原微生物生长和增殖需要铁，血液中铁的含量大幅下降。因此，减少日粮中铁的供应可能会是一种有效的干预策略，这样能帮助生病动物抵抗疾病，甚至防止感染。实验管理中，抗病猪的过剩铁被证明是导致恢复时间延长的原因。最后，免疫应激动物血液中铜含量增加，因为IL-1增强了铜蓝蛋白的合成，这是一种急性期蛋白，它增强了淋巴细胞的反应。
维生素

    很少有资料是关于疾病期维生素需求的。维生素E和硒的缺乏降低感染动物淋巴细胞的增殖，这一信息已经被证明，而这些营养过剩增加了抗体生长和淋巴细胞的增殖，这些都是非常有益的成分。其他天然抗氧化剂目前是未知的，但是也被认为是有相似作用功能的。另外，维生素A缺乏与减少上皮完整度有关，这样潜在地促进了病原体物质通过胃肠道或者呼吸道系统的感染。

结论

    以上信息只是针对这个令人兴奋的话题作一个简短的介绍，也是对许多研究的一个指导，研究需要充分理解这个主题。对于在疾病时期营养需求更深的认识将促进动物更快地恢复，减少疾病对生长性能的消极影响。

英文原文

How disease affects nutrient requirements

Date: 2013-02-04

Ioannis Mavromichalis, Ph.D.,

Sick animals eat less feed, but it appears they also have different nutrient requirements.

During disease a metabolic alteration from anabolism to catabolism is considered essential for the success of the immune system response, as nutrients must be redistributed away from growth to the support of immune system functions to control the pathogenic infection. However, today there is very little quantitative data to enable nutritionists to formulate diets specifically for sick animals.
Immune system responses
It is widely understood that exposure to pathogens triggers the animal’s immune system, which in response releases a host of pro-inflammatory cytokines that modulate not only the immune response, but also, overall metabolism. Research has demonstrated clearly that activation of the immune system by these cytokines (even at subclinical levels) depresses appetite and reduces muscle protein synthesis, while increasing muscle protein degradation. Thus, the metabolic state of the diseased animal switches from anabolism (growth) to catabolism (muscle loss).
Naturally, when the immune system is activated, metabolism is directed towards the synthesis of immune system compounds. As it happens, nutrient requirements for these processes are quite different than requirements for normal growth. Today, there is a real lack of meaningful information regarding the nutrient requirements of diseased animals. All “standard” nutrient requirements have been traditionally derived from dose-titration experiments with relatively healthy pigs reared under near optimal conditions.
Amino acids
The immune system has its own unique set of amino acid requirements, which differ from that required for growth. For instance, acute-phase proteins produced by the liver in response to cytokines have a different amino acid composition than skeletal muscle proteins: the aromatic amino acids (phenylalanine, tyrosine, and tryptophan) are found in larger concentrations in acute phase proteins, which are produced in massive quantities in the liver at the onset of disease. It has actually been suggested that excessive muscle degradation is due to the differences in amino acid profile between muscle protein and acute phase proteins.
In addition, threonine is a major component of immunoglobulin-G and obviously higher dietary concentrations of threonine are required for antibody production than for body growth in pigs.  Additionally, immunological stress causes an increase in amino acid maintenance needs as a proportion of total requirement. Overall, it appears that requirements for many amino acids may be increased in challenged pigs, whereas lysine requirements could be much lower.
Minerals
When it comes to minerals, it is already known that a deficiency of zinc greatly reduces immunocompetency and increases the chances of infection. However, zinc hyper-alimentation may also complicate the immune response of infected pigs because it may interfere with normal immune system functions. Indeed, pharmacological dosages of zinc oxide for a prolonged period of time have been often associated with depressed performance.

In addition, as iron is required for the growth and proliferation of most pathogenic microorganisms, blood iron levels are dramatically reduced during infection. Thus, reducing dietary iron supplementation may be a useful intervention strategy to help diseased animals combat or even prevent an infection. Experimental administration of excess iron in challenged pigs has been shown to result in increased time to recovery. Finally, immunologically stressed animals exhibit increased copper levels in plasma, because IL-1 enhances synthesis of ceruloplasmin, an acute phase protein that enhances lymphocyte response.
Vitamins
There is very little information on vitamin requirements during disease. A deficiency of vitamin E and selenium has been known to greatly reduce proliferation of lymphocytes in infected animals, whereas hyper-alimentation of these nutrients increases antibody production and lymphocyte proliferation; something that is highly beneficial. The role of other natural antioxidants is currently unknown, but it is believed to be along similar lines of action. In addition, vitamin A deficiency is associated with reduced epithelial integrity that could potentially facilitate the invasion of pathogenic agents via the gastrointestinal tract or the respiratory system.
Conclusions
The above can only serve as a brief introduction to this exciting topic and also as a guide towards more research that is needed to fully understand this issue. A deeper understanding of nutrient requirements during disease will enable animals to recover faster and reduce the negative effects of disease on growth performance.

英文来源：wattagnet.com

zhou7550

太感谢楼主了，倾情奉献！

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zhou7550 发表于 2013-5-19 20:27
太感谢楼主了，倾情奉献！

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