The Effects Of Levels Methionine In Low Protein Diets On Nitrogen Metabolism, Muscle Growth And Related Genes Expression In Broilers

As the source of protein in feeds gets more and more deficient, and the excessnitrogen excreted by livestock and poultries is causing the pollution, the animalnutritionist focused on the low protein technique. The animals fed low protein dietsonly could decreased the nitrogen excretion, thus it could prevent the pollutioncaused by animals. However, the low protein diets may influenced the performanceof animals. Thus, the objectives of this paper were to investigate the effects of levelsmethionine in low protein diets on nitrogen metabolism, muscle growth and relatedgenes expression in broilers.A total of3008-day-old Arbor Acres broiler chicks were randomly assigned tofive groups(Group A, Group B, Group C, Group D and Group E). The experimentaltime is from8-days-old to42-days-old. The Group A is the control group,the dietscontained normal CP (starter23%, finisher21%) and normal methionine (starter0.575%, finisher0.509%). The other four diets are low protein diets, the CP (starter21, finisher19%) is lower2%than diet A. The methionine level in diet B is lower0.07%than control diet, the methionine level in diet C is in accord with control diet,the methionine in diet D and E are higher1%and2%respectively than diet C.The feed intake and body weight were measured individually on a weekly basis.The FCR was calculated. The carcass characteristics were measured weekly from2-weeks-old. The breast yield, thigh yield and liver yield were collected and weighed.The ratio of breast, thigh and liver were calculated. The meat quality (pH, color,tenderness) were measured from4-weeks-old. The mRNA of MRFs, Pax3/7、MSTN、HSP25in breast muscle were measured by Real-time PCR. The Caspase-3mRNA in breast and liver was measured too.From15to21days old and from36to42days old, one chick (close to average body weight) was chosen to study the nitrogen metabolism. The Cr2O3markermethod was used to detect the digestibility of nitrogen and nitrogen excretion. At42days old, the serum profiles (BUN, UA, TP, GLOB, ALB, AST, ALT, ALP, Ca) weremeasured.The results showed that: there was no significance among these groups in bodyweight in42days old (P>0.05). The group B, C and D decreased the feed intake inwhole period (P<0.05). And there is a trend decreased the FCR in low protein dietsgroup (P>0.05). The group D decreased the breast weight in3weeks old (P<0.05),however the breast weight grow rapidly in group, in6weeks old the group Dimproved the breast weight (P<0.05). The group D decreased the liver weightsignificantly (P<0.05). There is no significance in meat quality among these groups(P>0.05).Group B decreased the digestibility of nitrogen in starter (P<0.05), the lowprotein diets decreased the chicken nitrogen excretion in some extent (P>0.05). Thelow protein diets decreased the UA and BUN in serum, group B and C decreased theUA in serum significantly (P<0.05), group B and E decreased the BUN in serumsignificantly (P<0.05).The group B down-regulated the expression of Caspase-3mRNA (P<0.05),group C and down-regulated the expression of Myogenin m RNA (P<0.05).In conclusion, the low protein diets could decreased the nitrogen excretion,adding DLM to low protein diets could raise the performance and improve the breastweight, the methionine deficient could enhance the expression Caspase-3, and thismay be one of the most important molecule regulate the breast growth.