The Effect And Mechanism Of Dietary Phosphate On The Intestinal Absorption Of Phosphorous In Broilers

Phosphorus is an essential nutrient and possesses numerous functions, both structural and metabolic,in all animals. For its characteristic of being absorbed relatively slowly by intestine of animal,phosphorus,an very expensive feed resource now, has been excharged into the environment by animalwaste, which definitely is harmful with ecological environment. In order to solve the problem above byanimal nutritional means, we conducted three trials to research the character of intestinal absorption ofphosphorus in broiler chichens.Trial one was conducted to investigate the effects of diets with different P content on P depositionin broilers on the macro level through length of tibia, Ca and P retentions in tibia as well as theconcentration of calcium and phosphate in serum. In a completely randomized design test,240ArborAcres broilers were assigned into five groups given experimental diets containing differentnon-Phytate Phosphorus (nPP) content (0.25%,0.35%,0.45%,0.55%,0.65%). The Ca content wasthe same (1.0%) in all diets. On days14,28and42, serum and tibia bone was collected for measuringthe length, ash content, Ca and P content in serum and tibia. The results were shown as following:(1)The tibia length of0.25%treatment was significantly shorter than that of other treatments whichrevealed significant difference (P<0.05).(2) The serum Ca declined as the dietary P level of dietincreased, and0.25%treatment was significantly higher than other treatments on day14.(3) Thecontent of Ca in tibia bone in0.25%treatment group was much lower than the others on day14, but itwas higher than the others on day28and42significantly.(4) The content of phosphorus in tibia boneof each treatment almost remained on the same level before day28, but it decreased significantly as Pcontent in diet increased on day42. From all the results above, it concluded that that the optimaldietary level of available phosphorus meeting the requirement for development of bone in broilers is0.45%when the dietary level of1.0%Calcium was provided.Trial two was conducted to study the effect of phosphorous deficient diet on absorption andtransportation of phosphate in the small intestine of broiler. In a completely randomized design test,one hundred and twenty eight Arbor Acres broiler chicks divided into four treatments with eachtreatment containing four replicates and8chicks per replicate were fed for42days (1-42days of age),the diet of four treatments contained0.2%、0.3%、0.4%and0.5%non-Phytate phosphorus respectively.The ability of absorbing phosphate by everted intestinal sac from each group was evaluated every twoweeks. The results revealed the absorption ratio of different intestinal sacs from two-week-old chicksdiffered significantly,which lowest in duodenum,and duodenum absorption decreased when thedietary phosphorus level increased.For four-week-old chicks,dietary phosphorus affected the intestinalabsorption ratio significantly,and the phosphorus absorption ratio in jejunum and illum of0.2%groupcome out higher than that of other groups (P<0.01). For six-week-old chicks,the phosphorusabsorption ratio of duodenum and jejunum sacs decreased as dietary phosphorus level increased,butno differences coulded be seen in illum. We got the conclusion that phosphorus absorption ratio by intestinal sacs from broilers decreased as dietary phosphorus level increased; The difference betweenphosphorus absorption ratio by intestinal sacs was obvious in the first two weeks,but disobvious in thelast four weeks.Trial three was designed to investigate the effect of diets of different P content on the expression oftype Ⅱ sodium phosphate cotransporter (NaPi-Ⅱb) in the brush border membrane of duodenumentercyte by real time RT-PCR.128Arbor Acres broiler chicks were randomly assigned into fourtreatments with each treatment containing four replicates fed diets of four treatments containing0.2%、0.3%、0.4%and0.5%total phosphate respectively, and1cm duodenum samples were collected on days14,28and42. The results showed that RT-PCR analysis demonstrated the presence of a single mRNAtranscript present predominantly in the small intestine, with the highest expression in the duodenum,followed by the jejunum and ileum. In situ hybridization indicated that the Na-Pi cotransporter mRNAis expressed throughout the vertical crypt-villus axis of the small intestine. Reduction of P in the diet ofchicks from hatch to14d of age resulted in a significant induction of Na-Pi cotransporter mRNAexpression in the small intestine.