Effects Of Different Dietary Starches On Intestinal Functions And Health And The Underlying Mechanism In Weaned Piglets

The health status and growth performance of animals mostly depend on the intestinal health. The relationship between nutrition and intestinal health is one of the most important studies in both traditional and modern clinical nutrition researches. Currently, the studies on the relationship between nutrition and intestinal health mainly focus on functional nutrients, such as amino acids, vitamins and fermentable carbohydrates. Starches are not only the main source of carbohydrates in grains, but also the major energy source for monogastric animals. However, there have been little researches about the correlation between different sources of dietary starch and intestinal health of weaned piglets. Additionally, intestinal microorganisms play an important role in immunity, nutrient intake as well as epithelial cell growth. The complex gut microflora are beneficial for intestinal health. However, the underlying molecular mechanisms by which intestinal microorganisms regulates intestinal health are poorly understood. The present study was designed to compare the effects of different sources of dietary starch on intestinal health of weaned piglets, and study the molecular mechanisms by which different dietary starches affect the intestinal health of weaned piglets. In this study, the influence of the different dietary starches (corn starch (CS), wheat starch (WS), tapioca starch (TS) and pea starch (PS) on growth performance, intestinal morphology and gut environment was investigated in 28 weaned pigs. In vitro cell culture experiments were then conducted to study the effects of main bacteria(Escherichia, Lactobacilli, and Bifidobacterium) as well as starch enzymolysis products on the expression of intestinal development (GLP-2, IGF-1, IGF-1R, EGF) and glucose transporters (SGLT-1 and GLUT-2) related genes. This study contains three experiments as follow:Experiment 1:Effects of different sources of starches on gut environment and intestinal morphology in weaned piglets.The aim of this experiment was to assess the effects of different starches (different amylose/amylopectin ratio) on performance, intestinal morphology and gut environment of weaned piglets. Twenty-eight 21±1.5-day-old Durocx (Landrace×Yorkshire) male piglets with initial BW of 6.5-7 kg were used in this experiment. The experimental pigs were distributed into four groups of seven piglets each according to body weight. Piglets in four treatments were fed diets containing corn starch, wheat starch, pea starch and tapioca starch as only carbohydrate-origin energy source, respectively.The results showed that:1. Amylose content and the amylose/amylopectin ratio were main factors of starch digestibility. The digestibility of different sources of starch was significantly different in different parts of small intestines. The digestibility of tapioca starch (low amylose and amylopectin ratio) was the highest and the digestible rate is the fastest, followed by these of corn starch and wheat starch. The digestibility of corn starch and wheat starch (similar amylose/amylopectin ratios) had no difference in all intestinal segments, while the digestibility of pea starch (high ratio of amylose and amylopectin) was the lowest among four starch diets.2. Our results indicated that the growth performance (daily feed intake, daily gain and F/G) of piglets was not affected by different dietary starches (0-21d).3. The intestinal morphology and enzyme activity were significantly affected by different dietary starches in piglets. The villus height and crypt depth of small intestines (duodenum, jejunum and ileum) in pea-starch-fed piglets were the highest among four starches. Long-term intake of PS with high amylose/amylopectin ratio dramatically increased the activity of amylase and maltase in pig intestines.4. The population and composition of intestinal microbials in piglets were significantly influenced by dietary starch sources. The population of Lactobacillus, Bifidobacterium and Bacillus were elevated in PS-fed group, whereas the populations of Escherichia were decreased in intestinal (duodenum, jejunum, ileum, cecum and colon) digesta of piglets.5. The concentrations of total short-chain fatty acids (SCFA) and the molar concentration of SCFAs (especially butyrate) were significantly influenced by dietary starch sources in the cecum and colon digesta. Feeding pea-starch (high amylose/amylopectin ratio) diet to piglets resulted in high SCFA concentration (especially, butyrate concentration and the molar ratio) in the cecum and colon digesta.6. The serum insulin and cholesterol concentrations were both elevated in TS-fed group. There was no significant difference between CS-fed and WS-fed groups.7. Feeding pea starch diet to piglets resulted in higher expression of intestinal development-related genes GLP-2, IGF-1, IGF-1R mRNA and glucose transporter SGLT-1 and GLUT-2 mRNA of small intestines. However, these genes were decreased in tapioca starch group. These results indicated that pea starch (high ratio in amylose and amylopectin) could increase the proliferation of intestinal beneficial bacteria (Lactobacillus, Bifidobacterium and Bacillus) in piglets and decrease the amount and ratio of Escherichia.A long-term intake of pea starch could improve intestinal morphology and enzyme activity, and increase villus height and crypt depth in duodenum, jejunum and ileum. Long-term intake of pea starch could increase expression of intestinal development-related genes GLP-2, IGF-1, IGF-1R and GLUT-2 and SGLT-1, which could promote the growth of small intestines and improve the intestinal morphology. Therefore, the starch of high amylose/amylopectin ratio (i.e. PS) may be more healthful for intestines of weaned piglets as the dietary energy sources.Experiment 2:Effects of intestinal microbial population on expression of intestinal development-related genes in IPEC-J2 cell line.The pig jejunum epithelial cell line, IPEC-J2 was used in this experiment to study the effect of intestinal main bacteria on the expressions of genes related to intestinal development and glucose transport carriers In this experiment, we determined the effects of different concentration of Lactobacillus, Bifidobacterium and Escherichia on IPEC-J2 cell proliferation. Moreover, different concentrations of Lactobacillus, Bifidobacterium and Escherichia were added into serum-free medium, in which IPEC-J2 cells were cultured for four hours. Total RNA were extracted and the expressions of related genes were evaluated.The results showed that:1. The cell proliferation of IPEC-J2 was significantly elevated after Lactobacillus and Bifidobacterium treatment for 48 hours.2. Expressions of mRNA levels of genes related to intestinal functions were up-regulated significantly by Lactobacillus and Bifidobacterium. The expression of mRNA of genes related to intestinal development and glucosetransport were down-regulated by Escherichia.These results indicated that intestinal microflora could influence intestinal cell proliferation and function-related gene expressions, which may be the important indirect mechanism that different starches have different effects on intestinal structure and functions.Experiment 3:Effects of enzymolysis products of different starches on mRNA expression of genes related to intestinal development in IPEC-J2 cell lineIn this experiment, we determined the effects of enzymolysis products of different starches on intestinal development of weaned piglets. We produced enzyme-hydrolyzed products of corn starch, tapioca starch, wheat starch and pea starch with amylase and glycosidase in vitro. IPEC-2 cell line was used in the experiment as a model to investigate the effects of enzymolysis products of different starches on mRNA expression of genes related to intestinal development (GLP-2,EGF,IGF-1,IGF-1R) and glucose transport. The results showed that enzymolysis product of pea starch was significantly up-regulated mRNA expression of GLP-2, GLUT-2 and SGLT-1 compared with other groups, whereas these genes were down-regulated by enzymolysis product of tapioca starch. The enzymolysis products of corn starch and wheat starch (similar ratio of amylose to amylopectin) did not impact mRNA expressions of these genes. The result indicated that enzymolysis products of starches in vitro could promote the mRNA expression of GLP-2, GLUT-2 and SGLT-1 genes, which may be the important direct mechanism that different starches have different effects on intestinal structure and functions.In conclusion, the present results demonstrate that different starches have different regulatory effects on intestinal micro-ecological environment of piglets. Pea starch as dietary energy source may be more healthful for intestines of weaned piglets by improving intestinal environment, maintaining intestinal morphological structure and promoting intestinal development. Effects starches on intestinal structure and function may be achieved by the direct effect of hydrolysis products of starch on intestinal epithelium and the indirect effects of change of microfloral profile. The underlying molecular mechanisms are associated with the expression changes of genes related to intestinal structure and function.