Molecular Mechanism Study Of Early Dietary Energy Level On Intestinal Phosphate Transportation In Broilers

Feed restriction to broilers could alleviate a series of diseases due to high growth rate.Low dietary nutrient density could not only control the growth rate of broilers,but also avoid the starvation induced by feed restriction,whereas in the meanwhile,the phosphate transport in small intestine of broilers was also declined with the mechanism unknown.We first discussed the interactive impact of early dietary energy and non-phytate phosphorus on subsequent growth of young broilers.Then analyze the small intestinal phosphate transport and AMPK signal pathway.At last,the activator and inhibitor of AMPK were used to further clarify the effect of AMPK on intestinal phosphate transport affected by dietary energy.Experiment 1 was taken to determine the interactive impact of early dietary energy and non-phytate phosphorus on subsequent growth performance,intestinal development and bone parameters of young broilers.A 3 × 3 factorial experiment consisting of three levels(low,medium,and high)of energy(LE,ME,and HE)with three levels of non-phytate phosphorus(NNP;LP,MP,and HP)was conducted.Treatments were continued from 1 to 21 days of age,after which the same standard diets were fed until 35 days of age.The results showed that:(1)LE decreased the body weight gain(BWG)of broilers fed the MP and HP diets.A starter LE diet induced significant compensatory growth in LP fed groups,as compared with other NPP groups.(2)LE decreased VH of intestine,and high NPP further induced the lowest CD and the highest VH/CD ratio of broilers in the early growth period.However,in the later period,the VH/CD ratio of broilers fed the LE-LP diet increased.(3)The tibia breaking strength,as well as the phosphorus and calcium contents in the tibia,were significantly decreased in broilers fed a low-NPP diet,as compared to those in the MP and HP groups.LE significantly increased tibia ash content of broilers especially in LP groups in starter phase.At 35 days of age,the tibia breaking strength of broilers fed the LP diet was significantly decreased,while the phosphorus and calcium contents in the tibia were increased.The results suggested that low energy and low phosphorus in early diet had significant compensation and interaction effect on subsequent growth performance and intestinal development of broilers.Higher dietary energy or phosphorus during starter phase did not produce superior later growth.Experiment 2,in order to determine changes in intestinal phosphate transport in young broilers due to dietary energy restriction and the possible underlying mechanism,a 3×3 factorial experiment consisting of three levels of energy with three levels of non-phytate phosphorus(NPP)was conducted.The results showed that LE increased ATP and decreased the AMP/ATP ratio in chick duodenum;and high NPP diet decreased ATP and EC,increased AMP and the AMP/ATP ratio.LE enhanced NaPi-IIb mRNA expression,but decreased p-AMPK/total AMPK ratio.These results suggest that although low dietary energy reduced the growth performance of broilers in the initial phase,it was beneficial for intestinal development and phosphate transport possibly by enhancing intestinal energy metabolism and regulating the AMPK signal pathway.Experiment 3,AICAR and Compound C treatment in vivo test was used to further demonstrate the relationship between AMPK signal pathway and intestinal phosphate transport affected by dietary energy levels.I.V.AICAR significantly increased plasma Ca level,decreased intestinal NaPi-II b mRNA expression,AMP and TAN content.Dietary energy had no effect on other indexes after I.V.AICAR.During the control group,low energy significantly decreased p-AMPK/T-AMPK ratio.After ip Compound C,energy had no effect on plasma Ca,but in the control group,low energy decreased plasma Ca level.ip Compound C significantly increased NaPi-IIb mRNA expression,and had a trend to decrease the p-AMPK/T-AMPK ratio and AMP content.Low and high energy had the trend to decrease the p-AMPK/T-AMPK ratio,low energy increased the p-mTOR/T-mTOR ratio.Compound C and energy had no significant interaction on AMPK signal related protein expression.In the control group,low energy significantly increased intestinal ATP content,decreased AMP/ATP ratio,no effect was found in the high energy group.In the ip Compound C group,both low and high energy decreased ATP and increased AMP/ATP ratio.In conclusion,low energy and low phosphorus in early diet had significant compensation and interaction effect on subsequent growth performance and intestinal development of broilers.Dietary energy could affect intestinal phosphate transport,energy metabolism and AMPK signal pathway.AICAR decreased while Compound C increased the mRNA expression of NaPi-IIb,both could affect the intestinal nucleotide metabolism,but had different effect on AMPK/ACC signal pathway.Except AMPK/ACC signal pathway regulated the intestinal phosphate transport affected by dietary energy,Ca2+ was might also be involved during the process.