中链脂肪酸在饲料中的用途

2017-6-23 09:58| 发布者: 畜牧编辑| 查看: 2816| 评论: 1|原作者: 畜牧编辑

　作者：于炳欣译来源：预混料家园（yuhunliaojiayuan）

　　在抗生素减少使用的趋势中，脂肪酸正在成为促进肠道健康的常用添加剂。

　　在乳猪断奶后，会发生许多变化，包括饲料、圈舍和分群，这些都是影响动物生长的已知应急。断奶后生长发育迟缓是仔猪常见的一种表现，如果断奶越早，则表现越明显。原因与低采食量和肠道发育不良有关。在猪的一生中，肠道的发育对它们的健康和生产性能至关重要。中链脂肪酸(MCFA)是天然产物，已在动物营养中使用了一段时间。研究表明，它们具有抗菌活性，并在肠道发育和免疫系统中发挥作用。考虑到减少饲料抗生素使用的压力，对MCFA的兴趣有所增加。

　　那么营养专家需要知道如何，为什么，什么时候考虑把它们使用在饲料中呢？

　　什么是中链脂肪酸？

　　中链脂肪酸是6~12个碳原子构成的脂肪酸，它是自然界中含量较少的脂肪酸，主要来源于母乳、牛奶及其制品、棕榈仁油和椰子油等。代表性的MCFA有：己酸（6），辛酸（8），癸酸（10）和月桂酸（12）

　　在消化方面，MCFAs被动地从胃肠道扩散到门静脉系统，不需要改变——不像长链脂肪酸。

　　MCFAs如何工作?

　　MCFAs影响肠道环境，通过这种方式，它们已经被证明会影响肠道菌群。微生物学家发现，它们对革兰氏阳性和革兰氏阴性菌有直接的抗菌作用。当对四种常见的影响猪(大肠杆菌，链球菌，沙门氏菌和产气荚膜梭菌)的病原体进行测试时，MCFA组合的最低抑制浓度在0.1 - 0.3%之间。

　　与猪常见的条件致病菌的抗菌活性。

　　他们还将为肠道提供一些能量，并改善肠道形态，包括绒毛高度。MCFAs是有益细菌的能量来源，改变肠道环境，阻止病原体的扩散。它们还具有抗病毒性质。其他研究也发现，它们可以减少某些病原体的毒性。

　　商业应用

　　MCFAs的混合物被作为饲料添加剂出售，被应用在各种动物生产中。产品还包括短链脂肪酸(SCFA)，如丁酸、丙酸和甲酸。这些有机酸与MCFAs之间有一定的协同作用。SCFAs破坏细菌细胞壁，让MCFAs进入内部。它们改变pH值，导致细胞爆裂。

　　MCFAs可以以甘油三酯的形式中出现，但这需要脂肪酶才能达到预期的效果。

　　对猪的好处

　　在乳猪饲料中，建议添加高水平的MCFAs，因为在乳猪的免疫系统仍在发育中，它们与各种微生物接触。

　　MCFA在断奶乳猪时期的益处已经在生长和饲料转化方面得到证实。MCFA还可以改善乳猪蛋白质和粗纤维的消化。

　　减少抗生素的使用

　　添加MCFA是减少抗生素使用的方法之一

　　欧盟有可能禁止氧化锌的使用，有助于防止断奶后腹泻的产品越来越引起关注。

　　美国营养专家最近公布的数据显示

　　对未来的影响

　　已经证实MCFA在有益菌繁殖和提高动物健康水平的作用，因此对于它们的用途值得进一步的研究。在某些情况下MCFAs对采食量的负面影响有一些担心。在组合的情况下，短、中、长链脂肪酸的水平和比例将对畜禽生产性能起到显著影响。

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引用畜牧编辑 2017-6-23 09:50: 附上原文英文版：

How to use medium-chain fatty acids in pig dietsIn a climate of reduced antibiotic usage, natural fatty acids are becoming popular additive for promoting gut health
During weaning — and shortly after — a lot of changes occur, including diet, environment and social grouping, which are known stressors that affect animal performance. Post-weaning growth retardation is a common phenomenon in pigs and one that is more pronounced if weaning is carried out early. The reasons for this are linked to lower feed intake and poor gut health. The development of the gut in young piglets and its maintenance throughout a pig's life are key to their health and performance.
Medium-chain fatty acids (MCFA) are natural products, which have been used in animal nutrition for some time. Research has shown that they have antibacterial activity, as well as playing a role in gut development and the immune system. Given the pressure to reduce the use of antibiotics in agriculture, interest in MCFA has grown.
So what do nutritionists need to know in terms of how, why and when to consider including them in pig diets?
What are medium-chain fatty acids?
MCFAs are fatty acids with aliphatic tails of six to 12 carbons, which can form medium-chain triglycerides (MCTs). They include the unbranched fatty acids: caproic acid (6), caprylic acid (8), capric acid (10) and lauric acid (12).
Commercially, MCFAs are extracted from coconut and palm oil. Goat’s milk is naturally high in the smallest three MCFAs, while sow's milk contains a significant amount of the largest.
In terms of digestion, MCFAs passively diffuse from the gastrointestinal tract into the portal system, without the need to be modified — unlike long-chain fatty acids.
How do MCFAs work?
MCFAs influence the intestinal environment and, in this way, they have been shown to affect the gut microflora (microbiome). Microbiologists have discovered that they have a direct antimicrobial affect on gram-positive and gram-negative bacteria.
When tested against four pathogens commonly affecting pigs (Escherichia coli, Streptococcus suis, Salmonella poona and Clostridium perfringens), the minimum inhibitory concentration for MCFA combinations was between 0.1 and 0.3 percent.

MCFAs have antibacterial activity against common pig pathogens. | Batovska, D., et al.
They will also provide the gut with some energy, and improvements in intestinal morphology, including villi height, have been observed.
MCFAs are an energy source for beneficial bacteria, therefore creating a gut environment that discourages the proliferation of pathogens. They also have anti-viral properties, being particularly effective against membrane viruses.
Other research has found that they may be able to reduce the virulence of certain pathogens. This may be due to an indirect immune effect or their ability to reduce viral shedding. These findings have led to their application in specific disease states, e.g. post-weaning multisystemic wasting syndrome (PMWS).
Commercial application
Blends of MCFAs are sold as feed additives to be included in a variety of production animal species. Products may also include short-chain fatty acids (SCFA), such as butyric acid, propionic and formic. There is a synergy between these organic acids and MFCAs, for which a greater-than-additive effect has been observed.
SCFAs acidify the gut and interrupt the bacterial wall, allowing MCFAs inside. They change the pH and cause the cell to burst. They also inhibit the production of lipase, an enzyme that bacteria require to attach to the gut wall.
MCFAs can be presented in the triglyceride form, but this requires lipase in order for them to have the desired effects. As salts, there can be palatability issues and aromas may be added to try and overcome this. They can be encapsulated to protect them as they pass through the duodenum and are released in the ileum and large intestine.
Other products are described as stable, but activated.
“By delivering MCFAs in this way means they are ready to act as soon as they are needed,” said Dr. Suzanne Petersen, senior business development manager with PMI Nutritional Additives. “Other catalysts, such as enzymes, aren’t required for them to work.”
Benefits in pigs
In the neonatal pig, a high level of MCFAs is recommended due to it being the time of greatest challenge. Piglets’ immune systems are still developing and they are coming into contact with a wide variety of microbial challenges.
The benefits of MCFAs in weaning pigs have been demonstrated in terms of better growth and feed conversion. This effect is particularly pronounced in times of challenge and fewer incidences of diarrhea have been reported. Studies have also shown that MCFAs can improve the digestion of protein and fiber in piglets.
Stresses during early grower phases may have a negative impact on pig performance. Diet changes, pig movement and re-established social orders may result in reduced feed intake and poorer gut health. By supporting gut health during these periods, MCFAs are included with the aim of optimizing pig performance.
There is also potential application in the late finishing period, when increased intake and feeder competition can cause stress. In terms of the sow, supporting her immunity and gut health can only be of benefit to her offspring and longevity in the herd.
Reducing antibiotic usage
MCFAs are one of the strategies being employed by producers wishing to reduce or remove antibiotics from their production.
“While there is no direct replacement for antibiotics, they are a useful tool, particularly post-weaning,” says Violet Beatie, research and technical manager, Devenish Nutrition. “They should be employed alongside improvements in management, nutrition and hygiene.”
With a potential EU ban on zinc oxide, products that could help prevent post-weaning diarrhea are particularly interesting.
American scientists decided to compare the performance of nursery pigs fed MCFAs with and without a commercial antibiotic program. The recently published data showed that MCFAs improved the performance of pigs fed a diet containing antibiotics. Similar weight gains and a numerical trend for improved feed efficiency were seen when compared with an antibiotic-free diet — with savings of $0.45 per pig.

Equivalent performance was observed between those pigs fed MCFAs alone or in combination with antibiotics. | McManus, D., et al.
Future implications
MCFAs have been shown to have a beneficial effect at the microflora and host animal level. Therefore, their use to support pigs in times of stress is worth further investigation.
As already discussed, their inclusion in antibiotic-free diets has potential. However, not all products are the same. Nutritionists should ensure that the MCFAs are pure, stable and well defined.
There is some concern about potential negative effects of MCFAs on feed intake in certain circumstances. This is one of the reasons the product specification and level of inclusion should be carefully considered for each life stage. In the case of combination products, the level and ratio of short-, medium- and long-chain fatty acids will have a significant effect on efficacy.
As with all feed additives, they need to pay for themselves – so potential performance improvements must be calculated. However, the benefits of MCFAs are becoming more widely accepted and will probably appear in pig diets more frequently.
References available on request.
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