| The progress of digestion, absorption and metabolism of dietary nitrogen nutrients is not isolated, their exists nesessary relationship between efficiency of dietary energy substances and the growth performance and effective utilization of dietary protein. Amino acids used for oxidation in gastrointestinal tract can be reduced by timely supply of dietary glucose. Thus, this will improve utilization of protein and reduce environmental pollution caused by excessive discharge of protein metabolites, which has an obvious theoretical significance, economic significance and environmental benefits. Although the dietary digestible energy values and crude protein content are described in various feeding standards, the source and composition of carbohydrates and fats for energy have not been demonstrated, and mechanisms of dietary energy structure on nitrogen utilization of piglets still need to be further studied. Therefore, comparative effect of different energy composition on growth performance were investigated in weaned pigs, and the differences of digestion, absorption and metabolism of dietary nitrogen were studied from both digestive tract and tissues of piglets to clarify the mechanism of energy composition on nitrogen utilization. This study contains two parts as follow: Experiment one: Effect of dietary glucose release characteristics on nitrogen utilization in pigletsTwenty-four 9.80 ± 0.59 kg of Duroc × Landrace × Yorkshire piglets were used in this experiment, randomly divided into four experimental treatments, each treatment contains six pigs. Piglets in the four treatments were fed with diets containing four different structures, different release pattern of glucose, 20% corn starch, lactose, glucose and sucrose, respectively, based on corn-soybean meal diets. The digestible energy of diets were all 14.8 MJ / kg, content of crude protein were all 17%, and the amino acid content of each group remain to be basically consistent. After 28 days feeding, growth performance of piglets, regularation of metabolism, portal vein blood parameters, chyme glucose and amino acid content of each intestinal segment, digestive enzyme activity, intestinal mucosa glucose and amino acids transporter gene expression were measured to study the different glucose release characteristics on nitrogen digestion, absorption and metabolism of piglets. The results showed that:Digestion in vitro experiments showed that the glucose release pattern as follows: glucose release rate was the fastest in glucose group diet from 0 to 120 min, and corn starch group was the slowest. But after 180 min, the other three groups were higher than glucose group.The results in vivo showed that: the free glucose concentration in duodenum was the highest in glucose group, the free glucose concentration in proximal jejunum of corn starch group was the lowest, and glucose concentration of lactose and corn starch group in distal jejunum was higher than glucose group significantly(P<0.05), glucose concentration in the ileum of corn starch group was the highest, glucose was the lowest. Total free amino acid concentrations in glucose and sucrose group were significantly higher than the contents of corn starch group(P<0.05), total free amino acid concentrations in proximal jejunum of glucose group were significantly higher than corn starch group(P<0.05), and the difference of total free amino acid concentrations in distal jejunum among four groups were not significant, the total free amino acid concentration of ileum chyme in corn starch and glucose group was significantly higher than sucrose group(P<0.05).The results of growth performance and nutrient metabolism showed that: in the first week, lactose, glucose and sucrose group showed a higher growth performance, ADFI of piglets and ADG were significantly higher than corn starch group(P<0.05). F/G of lactose and sucrose group were also significantly higher than corn starch group(P<0.05); in the second week, ADFI was still significantly higher in each added sugar group, but the differences of ADG and F/G between glucose and corn starch group were disappeared; the growth performance were similar in lactose and sucrose group in the whole test, and were significantly higher than the corn starch and glucose group(P<0.05). Nitrogen deposition in Lactose and sucrose group was significantly higher than the group of corn starch group and glucose group(P<0.05). Plasma alkaline phosphatase activity in lactose and sucrose group was significantly higher than the group of corn starch and glucose group(P<0.05). Portal vein serum total free amino acids in lactose and sucrose group were significantly higher than corn starch group(P<0.05). Pancreatic amylase activity had no significant difference among the four groups(P>0.05). But trypsin activity in glucose group was significantly higher than that of corn starch group(P<0.05). The effects of dietary glucose release characteristics on protease activity in each segment of intestinal contents had a significant difference(P<0.05), and disaccharide activity in each segment of the small intestine mucosa also changed significantly(P<0.05).Effects of dietary glucose release characteristics on intestinal glucose transporter SGLT1, amino acids transporter B0 +, EAAC1 and peptides transporter PepT1 mRNA expression levels were significant. Expression of SGLT1 mRNA in duodenum in diet group of the fastest glucose release was highest, expression of SGLT1 mRNA in proximal jejunum in glucose and sucrose group was significantly higher than the group of lactose and corn starch(P<0.05). Expression of SGLT1 mRNA of distal jejunum in lactose group was significantly higher than the other three groups(P<0.05). Expression of SGLT1 mRNA of ileum in corn starch, lactose and sucrose group was significantly higher than the glucose group(P<0.05). Expression of B0+ mRNA of duodenum and proximal jejunum in lactose group was significantly higher than sucrose group(P<0.05), expression of B0+ mRNA of distal jejunum in lactose, glucose and sucrose group was significantly higher than corn starch group(P<0.05), relative expression of B0+ mRNA of ileum in lactose group was the highest. Relative expression of EAAC1 mRNA of duodenum and proximal jejunum in corn starch group was the highest. Expression of PepT1 mRNA of duodenum and proximal jejunum in corn starch group was higher than the other three groups(P<0.05). Relative expression Pep T1 mRNA of distal jejunum in lactose group was the highest(P<0.05), expression of PepT1 mRNA of ileum in corn starch group was the highest(P<0.05), the difference in the other three groups were not significant(P>0.05). Experiment two: Effect of dietary carbohydrate/fat ratio on digestion and metabolism of nitrogen of piglets and mechanismEighteen 9.85±0.81 kg kg of Duroc × Landrace × Yorkshire piglets were used in this experiment, piglets were randomly divided into three experimental treatments, each treatment contain six pigs. Digestible energy of experimental diets were 14.8 MJ / kg, content of crude protein were all 17%, dietary carbohydrate energy value and fat energy value were respectively 11.7:1.0(low fat, LF), 1.5:1.0(middle fat, MF) and 1.0:6.9(high fat, HF). After 28 days feeding, growth performance of piglets, regularation of metabolism, portal vein blood parameters, each segment of intestinal chyme glucose and amino acid content, digestive enzyme activity, gene expression of glucose and amino acids transporter of intestinal mucosa, and protein expression both energy and protein metabolism in muscle of piglets were measured to study the difference of energy value ratios on nitrogen digestion, absorption and metabolism of piglets and mechanism. The results showed that:The ADFI and ADG was significantly reduced, F/G was significantly increased in Piglets consuming MF and HF diet at the initiation of the experiment(P<0.05), and in the whole test ADFI and ADG was significantly reduced in piglets consuming MF and HF diet(P<0.05). The apparent digestibility of dry matter, fat and protein were significantly reduced in Piglets consuming MF and HF diet(P<0.05). Intake nitrogen were significantly lower in piglets consuming MF and HF diet compared to LF(P<0.05), however the fecal nitrogen was significantly increased(P<0.05), nitrogen deposition was significantly decreased. Plasma total protein content in LF group was significantly higher than HF group(P<0.05), albumin, alkaline phosphatase, blood urea nitrogen, blood glucose and insulin among these three groups had no significant differences. Plasma Leptin and triglyceride levels were significantly increased in piglets consuming HF diet(P<0.05).Trypsin activity and amylase activity of pancreatic was significantly increased in piglets consuming LF diet(P<0.05), lipase activity of pancreatic were significantly lower in piglets consuming LF and MF diets(P<0.05).Lipase activity of intestinal contents of was significantly increased in piglets consuming HF diet compared with piglets consuming MF and LF diets(P<0.05). Effect of dietary carbohydrate/fat on protease activity of intestinal contents was significant(P<0.05), small intestine disaccharide activity and gene expression was also significant(P<0.05). With increased of dietary fat, the concentration of glucose in the gut was decreased, the concentration of free amino acids of duodenum in piglets consuming LF diet was significantly higher than the piglets consuming HF diet(P<0.05), and HF was significantly higher than LF group in distal jejunum(P<0.05), HF and MF group was significantly higher than LF group in ileum(P<0.05). With decreased of dietary carbohydrate/fat energy value ratio, the expression of SGLT1 mRNA were significantly decreased in each intestinal segments(P<0.05), expression of PepT1, B0 + and EAAC1 mRNA of duodenal mucosa in HF was the highest, Jejunum and ileum mucosa was increased in pigs consuming LF diet. Phosphorylation level of AMPK protein in skeletal muscle was significantly increased in pigs consuming HF diet compared with pigs consuming LF diet(P<0.05), protein expression of mTOR and its downstream protein S6K1 and 4E-BP1 was significantly decreased in pigs consuming HF diet(P<0.05).The above studies showed that the glucose release characteristics of different diets and carbohydrate/fat energy value ratio of dietary could influence the growth performance of weaned pigs, glucose release rate is too fast or too slow will affect the effective utilization of dietary protein. Piglets consuming LF diet had higher protein digestibility and nitrogen deposition ratio compared with piglets consuming HF diet. |
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