Effects And Mechanisms Of Rumen-protected Leucine On Starch Digestion And Utilization In Small Intestine Of Goats

Starch is the main source of energy for high-yielding ruminants.Most of the ingested starch is degraded by microorganisms in the rumen into volatile fatty acids and then gluconeogenesis into glucose through the liver,and the other part reaches the small intestine through the rumen and is directly digested into glucose.The energy utilization efficiency of starch digestion in the small intestine is much higher than that of degradation in the rumen.At the same time,too much starch degradation in the rumen can easily cause diseases such as rumen acidosis.Enabling more starch to digest in the small intestine is an energy-efficient and healthy nutritional regulation method.However,the digestion of starch in the small intestine of ruminants is restricted by insufficient secretion of pancreatic α-amylase.Studies have shown that leucine can stimulate the secretion of pancreatic α-amylase in adult ruminants and the development of pancreas in juvenile ruminants.However,in production practice,whether leucine can effectively promote pancreatic enzyme secretion to improve the digestibility of ruminant small intestine starch and the mechanism of leucine promoting pancreatic enzyme secretion need to be further explored.The research group had conducted amino acid addition experiments on ruminants through small bowel intubation surgery in the early stage.In order to avoid possible test errors caused by surgery to the experimental animals,in this study,young dairy goats were treated by adding rumen-protected leucine and rumen-protected lysine.We hypothesized that leucine can act as a signal molecule to promote pancreatic enzyme secretion and increase starch digestion in the small intestine.Detect production performance,blood biochemical indicators,small intestinal starch digestibility,pancreas and small intestinal chyme digestive enzyme activities and other indicators,comprehensive evaluation of the effect of rumen-protected leucine on the digestion of starch in the small intestine of dairy goats,and compare the differences in the mechanisms of leucine and lysine regulating the digestion of small intestine starch and the secretion of pancreatic enzymes,clarify the mechanism of leucine regulation of pancreatic enzyme secretion,and provide research basis for amino acid addition to improve ruminant production performance and feed utilization.Exp.1 The effect of rumen-protected leucine and rumen-protected lysine on the production performance,blood biochemical indicators,and digestion of small intestinal starch in young dairy goatsEighteen healthy Guanzhong dairy goat rams with similar weight were selected and randomly divided into three groups.Control group: fed with basal diet;Rumen-protected leucine group(RP-Leu): basic diet +17.45 g/d RP-Leu(actually reach the small intestine is 9g/d Leu);Rumen-protected lysine group(RP-Lys): basic diet +28.94 g/d RP-Lys(actually reach the small intestine is 9 g/d Lys).The pre-feeding period is 14 days,and the trial period is 49 days.Measure your body weight on the 1st and 49 th day.Blood was collected from the jugular vein 2 h after morning feeding on the 49 th day,and rumen fluid was collected at 4 h.Detect blood biochemical indicators and rumen fermentation parameters.The results showed that dietary supplementation of RP-Leu can significantly increase the body weight gain(P<0.05)and blood triglyceride concentration(P<0.05)of dairy goats compared with the control group,which tends to increase the insulin concentration(P<0.10).Carcass weight,other blood indicators,and digestibility of nutrients in the small intestine had no apparent effect(P> 0.05).The addition of RP-Lys significantly increased the blood triglyceride concentration compared with the control group(P<0.05),but had no effect on other indicators(P> 0.05).The addition of RP-Leu had no effect on the above indicators compared with the addition of RP-Lys(P> 0.05).Exp.2 The effect of rumen-protected leucine and rumen-protected lysine on thechymase activity,pancreas development and expression of pancreatic digestive enzymes in dairy goatsOn the basis of Experiment 1,it was found that although adding RP-Leu did not significantly improve the digestibility of small intestinal starch,it was numerically improved,and the weight gain of dairy goats was significantly increased.This experiment intends to study the possible effects of leucine and lysine on pancreatic enzyme secretion,pancreatic development and small intestinal glucose transport from the molecular mechanism level.After the trial period,each group randomly selects 5 dairy goats for slaughter,and collects pancreas and small intestine chyme samples.The digestive enzyme activity in pancreas and small intestine chyme was measured using the kit.Quantitative PCR was used to detect the m RNA expression levels of pancreatic amylase,trypsin,lipase,and small intestinal glucose transporters(SGLT1,GLUT2).Western-blot technology was used to detect the phosphorylation level of key proteins downstream of the mTOR pathway.The test results show that the addition of RP-Leu can significantly increase the activity of duodenal chyme α-amylase compared with the control group(P<0.05),and tend to increase the phosphorylation level of pancreatic protein 4EBP1(P<0.10)and the pancreas trypsin activity(P <0.10),for small intestine chymotrypsin activity,chymotrypsin activity,pancreas development,pancreatic digestive enzyme activity,pancreatic digestive enzyme m RNA expression,small intestinal glucose transporter m RNA expression,and pancreatic S6K1 phosphorylation level has no significant effect(P> 0.05).The addition of RP-Lys had no effect on the results compared with the control group(P> 0.05).Therefore,this study shows that leucine as a signal molecule activates the mTOR pathway and promotes α-amylase activity,thereby improving the digestion of starch in the small intestine of young dairy goats and improving production performance.Lysine does not stimulate pancreatic function.