中鏈脂肪酸在飼料中的用途

畜牧編輯

　作者：于炳欣譯  來源：預混料家園（yuhunliaojiayuan）

　　在抗生素減少使用的趨勢中，脂肪酸正在成為促進腸道健康的常用添加劑。

　　在乳豬斷奶后，會發生許多變化，包括飼料、圈舍和分群，這些都是影響動物生長的已知應急。斷奶后生長發育遲緩是仔豬常見的一種表現，如果斷奶越早，則表現越明顯。原因與低采食量和腸道發育不良有關。在豬的一生中，腸道的發育對它們的健康和生產性能至關重要。中鏈脂肪酸(MCFA)是天然產物，已在動物營養中使用了一段時間。研究表明，它們具有抗菌活性，并在腸道發育和免疫系統中發揮作用。考慮到減少飼料抗生素使用的壓力，對MCFA的興趣有所增加。

　　那么營養專家需要知道如何，為什么，什么時候考慮把它們使用在飼料中呢？

　　什么是中鏈脂肪酸？

　　中鏈脂肪酸是6~12個碳原子構成的脂肪酸，它是自然界中含量較少的脂肪酸，主要來源于母乳、牛奶及其制品、棕櫚仁油和椰子油等。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被動地從胃腸道擴散到門靜脈系統，不需要改變——不像長鏈脂肪酸。

　　MCFAs如何工作?

　　MCFAs影響腸道環境，通過這種方式，它們已經被證明會影響腸道菌群。微生物學家發現，它們對革蘭氏陽性和革蘭氏陰性菌有直接的抗菌作用。當對四種常見的影響豬(大腸桿菌，鏈球菌，沙門氏菌和產氣莢膜梭菌)的病原體進行測試時，MCFA組合的最低抑制濃度在0.1 - 0.3%之間。

　　與豬常見的條件致病菌的抗菌活性。

　　他們還將為腸道提供一些能量，并改善腸道形態，包括絨毛高度。MCFAs是有益細菌的能量來源，改變腸道環境，阻止病原體的擴散。它們還具有抗病毒性質。其他研究也發現，它們可以減少某些病原體的毒性。

　　商業應用

　　MCFAs的混合物被作為飼料添加劑出售，被應用在各種動物生產中。產品還包括短鏈脂肪酸(SCFA)，如丁酸、丙酸和甲酸。這些有機酸與MCFAs之間有一定的協同作用。SCFAs破壞細菌細胞壁，讓MCFAs進入內部。它們改變pH值，導致細胞爆裂。

　　MCFAs可以以甘油三酯的形式中出現，但這需要脂肪酶才能達到預期的效果。

　　對豬的好處

　　在乳豬飼料中，建議添加高水平的MCFAs，因為在乳豬的免疫系統仍在發育中，它們與各種微生物接觸。

　　MCFA在斷奶乳豬時期的益處已經在生長和飼料轉化方面得到證實。MCFA還可以改善乳豬蛋白質和粗纖維的消化。

　　減少抗生素的使用

　　添加MCFA是減少抗生素使用的方法之一

　　歐盟有可能禁止氧化鋅的使用，有助于防止斷奶后腹瀉的產品越來越引起關注。

　　美國營養專家最近公布的數據顯示

　　對未來的影響

　　已經證實MCFA在有益菌繁殖和提高動物健康水平的作用，因此對于它們的用途值得進一步的研究。在某些情況下MCFAs對采食量的負面影響有一些擔心。在組合的情況下，短、中、長鏈脂肪酸的水平和比例將對畜禽生產性能起到顯著影響。

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畜牧編輯

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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