斷奶仔豬胃腸道的飼喂

monica

FEEDING THE GASTROINTESTINAL TRACT AFTER WEANING
                                                 斷奶仔豬胃腸道的飼喂

Burrin and Stoll (2003) highlighted the temporal changes in gastrointestinal development and growth after weaning, showing that early-weaned pigs (14 days in this case) have an “acute phase” lasting about 7 days and a subsequent “adaptive phase” in which the gastrointestinal tract recovers from the immediate post-weaning insults. Although the duration and magnitude of these phases varies according to factors such as weaning age, environment, genotype and health status, they are generally coincidental with patterns of energy intake and weight gain after weaning (Le Dividich and Seve, 2000), although the variation surrounding these indices can be enormous (Brooks and Tsourgiannis, 2003). Feeding programmes and feed budgets after weaning have evolved to accommodate these two phases and place pigs as soon as possible onto cheaper diets, but the percentage of pigs in a population that fit this generalized pattern is unknown. Indeed, what are the implications for pigs that fall outside this pattern?

Burrin and Stoll (2003)強調了仔豬斷奶后胃腸道生長發育的短期變化，認為早期斷奶(14 天)后有一個為期約7天的“敏感階段”及隨后的“適應階段”，在“適應階段”仔豬的胃腸道會從斷奶后的損害中恢復過來。雖然這兩個階段的持續時間及影響程度隨斷奶日齡、環境、豬的基因型和健康狀況的不同而有差異（而這些指標通常都是千差萬別Brooks and Tsourgiannis, 2003），但是這兩個階段通常都和斷奶后能量采食及增重息息相關的(Le Dividich and Seve, 2000)。基于斷奶后飼喂程序和飼料開支的考慮，豬場通常都采用這兩個階段進行飼養，而且會盡可能快地讓豬吃上便宜的日糧，但是豬群中適用這種大眾化模式的豬到底有多少？不得而知。而事實是：對于不能適應這種飼養模式的豬而言，這又意味著什么？

In this regard, Burrin and Stoll (2003) remarked that given increases in the understanding of intestinal nutrient utilization of recent times, it is (theoretically perhaps) possible to formulate diets for weanling pigs with the specific goal of optimizing the growth, function and health of the gastrointestinal tract. Their review comprehensively describes some of the most promising candidates they believe could be used in weanling pig diets based upon their known mode(s) of action in the gastrointestinal tract and their utilization in the portal-drained viscera (PDV), the tissues of which include the stomach, pancreas, small and large intestine, and the spleen. In pigs, the PDV tissues contribute approximately 5% of body weight yet account for 20-35% of whole-body protein turnover and energy expenditure (Yen et al., 1997), which reflects their disproportionately high fractional protein synthesis rates and O2 consumption. The high rates of metabolism and nutrient utilization in the gut are directly linked to the high rates of proliferation, protein secretion, apoptosis and desquamation of various epithelial and lymphoid cells within the mucosa (Burrin and Stoll, 2003), all of which are a key feature of the post-weaning period.

就這一點，Burrin and Stoll (2003)就提出過：當前要更好的理解小腸對營養物質的利用，在原理上，為達到胃腸道的理想生長、功能和健康的特定目的來配制斷奶仔豬日糧，這也是完全可行的。根據Burrin and Stoll (2003)的回顧：基于一些物質在胃腸道發揮作用的方式以及它們在PDV組織中的作用，這些物質是斷奶仔豬日糧配制中很有幫助的指標，PDV組織包括胃、胰腺、小腸和大腸以及脾臟。 對豬來說，PDV組織約占體重的5%，但是卻占機體蛋白周轉和能量消耗的20-35%，這一點體現在PDV組織不成比例的高蛋白合成速度和氧氣的消耗上。 腸道代謝和營養物質利用的高效率直接與粘膜內不同的上皮和淋巴細胞的本身增殖、蛋白分泌、細胞死亡和脫落有關，這些上皮和淋巴細胞對斷奶后仔豬生長和發育都很關鍵。

Gut specific nutrients suggested by Burrin and Stoll (2003) include the amino acids glutamine, glutamate and threonine, and the reader is directed towards this review for more extensive information. Glutamine and glutamate are not considered as “essential” amino acids in traditional diet formulations, however there is a large body of evidence in many species, including young pigs, showing some benefits to the addition of these amino acids in the immediate post-weaning period. Arginine, an essential amino acid for neonates but not for growing pigs, was shown by Wu et al. (2004) to decline markedly in plasma during suckling, and supplementation of 0.2 and 0.4% arginine to 7- to 21-day-old artificially-reared pigs increased piglet growth rates by 28 and 66% respectively. Whether there is a conditionally essential requirement for arginine after weaning has not been investigated to my knowledge, however for producers that feed pigs milk liquid diets then attention to arginine levels may be warranted. Obviously major consideration for any of these amino acids of course is the cost of such interventions.

Burrin and Stoll (2003)提到，腸道的特定營養物質包括谷氨酸，谷氨酸鹽和蘇氨酸，讀者可以直接根據他們的回顧得到更多的信息。在傳統日糧中谷氨酸和谷氨酸鹽都不被認為是必需氨基酸，然而，有大量不同動物包括小豬在內的證據表明，在剛斷奶后仔豬日糧中添加谷氨酸和谷氨酸鹽確實有效。精氨酸，對于剛出生的乳豬來說是必需氨基酸，但對生長豬來說則不然，根據Wu等(2004)的研究表明乳豬在吃奶期間血漿內精氨酸顯著下降，給出生后7-21天的乳豬人工飼喂0.2%和0.4%的精氨酸，生長速度分別提高了28%和60%。雖然我自己的研究中并沒有進行關于精氨酸是否是條件必需性氨基酸的研究，但是對于那些飼喂液體奶的生產者來說，應該關注精氨酸的水平。 顯而易見，考慮上述任何一種氨基酸都會帶來成本的變化。

In addition, the influence of post-weaning infections and associated inflammatory responses on aspects of gastrointestinal function warrants mention. Burrin and Stoll (2003) suggested that enteric infection increases intestinal nutrient requirements that in turn limit the availability of dietary nutrients for growth. Key questions include how an infection, such as enterotoxigenic Escherchia coli infection, alters the pattern of intestinal nutrient utilization, and what are the key nutrients that may either become limiting for intestinal function/body growth and/or assist with gastrointestinal repair. In the case of enterotoxigenic Escherchia coli infection for example, which can still be prevalent 10-12 days after weaning, it seems ironic that some pigs in a pen could be offered a lower specification diet just at the time they require a higher specification diet to boost gut repair. Economics and facility management obviously play key roles in addressing this, however from a biological perspective I think this is an interesting question and one worth discussing.

此外，要提一下斷奶后的感染及炎癥對腸道功能的影響。 Burrin and Stoll (2003)建議，腸道感染增加了對營養物質的需要，進而限制了日糧中本來用來生長的養分利用率。一些關鍵的問題，包括產腸毒素大腸桿菌感染，是怎樣改變了小腸營養物質利用的模式，從而使一些重要的養分，或許也就變成了小腸機能/機體生長和/或腸道修復的限制性因子。拿產腸毒素大腸桿菌感染作為例子，在斷奶后10-12天仍然是主發疾病，但是比較有諷刺意味的是，在一個欄內本來需要特定日糧來滿足腸道修復需要，但是卻提供了普通的日糧。雖然經濟目的和設備管理更多地決定了日糧的使用，然而從生物角度來講，我認為，這是一個比較有意思的話題，值得探討。