断奶仔猪胃肠道的饲喂

monica

FEEDING THE GASTROINTESTINAL TRACT AFTER WEANING
                                                 断奶仔猪胃肠道的饲喂

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)强调了仔猪断奶后胃肠道生长发育的短期变化，认为早期断奶(14 天)后有一个为期约7天的“敏感阶段”及随后的“适应阶段”，在“适应阶段”仔猪的胃肠道会从断奶后的损害中恢复过来。虽然这两个阶段的持续时间及影响程度随断奶日龄、环境、猪的基因型和健康状况的不同而有差异（而这些指标通常都是千差万别Brooks and Tsourgiannis, 2003），但是这两个阶段通常都和断奶后能量采食及增重息息相关的(Le Dividich and Seve, 2000)。基于断奶后饲喂程序和饲料开支的考虑，猪场通常都采用这两个阶段进行饲养，而且会尽可能快地让猪吃上便宜的日粮，但是猪群中适用这种大众化模式的猪到底有多少？不得而知。而事实是：对于不能适应这种饲养模式的猪而言，这又意味着什么？

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.

就这一点，Burrin and Stoll (2003)就提出过：当前要更好的理解小肠对营养物质的利用，在原理上，为达到胃肠道的理想生长、功能和健康的特定目的来配制断奶仔猪日粮，这也是完全可行的。根据Burrin and Stoll (2003)的回顾：基于一些物质在胃肠道发挥作用的方式以及它们在PDV组织中的作用，这些物质是断奶仔猪日粮配制中很有帮助的指标，PDV组织包括胃、胰腺、小肠和大肠以及脾脏。 对猪来说，PDV组织约占体重的5%，但是却占机体蛋白周转和能量消耗的20-35%，这一点体现在PDV组织不成比例的高蛋白合成速度和氧气的消耗上。 肠道代谢和营养物质利用的高效率直接与粘膜内不同的上皮和淋巴细胞的本身增殖、蛋白分泌、细胞死亡和脱落有关，这些上皮和淋巴细胞对断奶后仔猪生长和发育都很关键。

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，肠道的特定营养物质包括谷氨酸，谷氨酸盐和苏氨酸，读者可以直接根据他们的回顾得到更多的信息。在传统日粮中谷氨酸和谷氨酸盐都不被认为是必需氨基酸，然而，有大量不同动物包括小猪在内的证据表明，在刚断奶后仔猪日粮中添加谷氨酸和谷氨酸盐确实有效。精氨酸，对于刚出生的乳猪来说是必需氨基酸，但对生长猪来说则不然，根据Wu等(2004)的研究表明乳猪在吃奶期间血浆内精氨酸显著下降，给出生后7-21天的乳猪人工饲喂0.2%和0.4%的精氨酸，生长速度分别提高了28%和60%。虽然我自己的研究中并没有进行关于精氨酸是否是条件必需性氨基酸的研究，但是对于那些饲喂液体奶的生产者来说，应该关注精氨酸的水平。 显而易见，考虑上述任何一种氨基酸都会带来成本的变化。

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，要提一下断奶后的感染及炎症对肠道功能的影响。 Burrin and Stoll (2003)建议，肠道感染增加了对营养物质的需要，进而限制了日粮中本来用来生长的养分利用率。一些关键的问题，包括产肠毒素大肠杆菌感染，是怎样改变了小肠营养物质利用的模式，从而使一些重要的养分，或许也就变成了小肠机能/机体生长和/或肠道修复的限制性因子。拿产肠毒素大肠杆菌感染作为例子，在断奶后10-12天仍然是主发疾病，但是比较有讽刺意味的是，在一个栏内本来需要特定日粮来满足肠道修复需要，但是却提供了普通的日粮。虽然经济目的和设备管理更多地决定了日粮的使用，然而从生物角度来讲，我认为，这是一个比较有意思的话题，值得探讨。