Effects Of MHA-Zn On Production Performance And Gut Microbiota Of Broilers In Low-protein Diets

Poultry farming is experiencing rapid development,the shortage of dietary protein,and nitrogen pollution has also attracted particular the interest of scholars,who have begun to focus on low-protein(LP)diets to alleviate protein stress and nitrogen pollution.However,reducing dietary protein levels alone may negatively affect the performance of animals.Trace elements are essential nutrients for poultry,and their addition in appropriate amounts can improve poultry production performance,and zinc is an essential nutrient for the survival and growth of poultry,with organic zinc being more bioavailable than inorganic zinc.Therefore,the study was conducted to investigate on the effect and mechanism of MHA-Zn(methionine hydroxyl analogue chelated zinc,MHA-Zn)on production performances of broiler in LP diets.To investigate the appropriate dose of MHA-Zn in LP diets and to achieve the maximum protein bioavailability of broilers.216 one-day-old Arbor Acres broilers were randomly assigned to 4 dietary treatments with 3 replicates(18 broilers per replicate).The work included 4 different groups: Group A as the control group:normal protein diet(110 mg/kg MHA-Zn);test groups were LP diet groups with 70mg/kg MHA-Zn(Group B),90 mg/kg MHA-Zn(Group C)and 110 mg/kg MHA-Zn(Group D),respectively,for 42 days.Test one: The production performance,apparent total tract digestibility,slaughter performance,meat quality traits,immune organ indices,blood biochemical indices,and ileal morphology of broiler chickens were measured at the end of the feeding trial,and the results showed that at 42 days,there no significant difference was observed for edible part,feed conversion ratio between LP diet group(90 mg/kg MHA-Zn)and normal diet group(P>0.05),groups B and D had significantly lower body weights than Group C(P<0.01).The result showed that there were no statistical differences in the percentage of dressed,the percentage of half-eviscerated,the percentage of eviscerated and meat quality traits between Group C and Group A(P>0.05),the percentage of eviscerated and the sum of breast and leg muscle were significantly lower in Group B than in groups A and C(P<0.05),but there was no significant difference between groups B and D(P>0.05).And adding 90 mg/kg MHA-Zn in LP diet significantly improved apparent total tract digestibility(ATTD)of nutrients and ileal histomorphology compared to Group A(P<0.05).There were no significant differences in protein estimations(total protein,albumin and globulin)and immune organ index detected across groups(P>0.05).The SUN in groups B and C was significantly lower than in groups A and D(P<0.01).Test two: According to the results of test one,performance levels of LP diet Group C(90 mg/kg MHA-Zn)and control Group A were similar.To investigate part of the mechanism of its effect on production performance,16 S r RNA sequencing was performed on the cecal contents of Group A and Group C,and expression of genes related to ileal and jejunal nutrient absorption was analyzed.Results showed that the five dominant phyla were Firmicutes(65.88% vs.51.30%),Bacteroidetes(30.62% vs.44.95%),Proteobacteria(2.50% vs.1.67%),Tenericutes(0.51% vs.0.75%)and Synergistetes(0.028% vs.0.25%)in Group A and Group C,at the genus level,Bacteroides(24.61% vs.36.91%),Faecalibacterium(7.05% vs.4.30%),Oscillospira(6.82% vs.3.93%),Ruminococcus(6.19% vs.3.18%)and Phascolarctobacterium(1.84% vs.2.56%)are the main dominant bacteria.Adding LP diet with 90 mg/kg MHA-Zn was adequate for production performance of broilers,it can promote beneficial bacteria of cecum(Lactobacillus,Butyricoccus,Oscillospira 等.)(P<0.01),at the same time,the expression of SGLT1,Pep T1 and MCT4 in the ileum and the expression of Pep T1 and MCT4 in the jejunum were significantly increased(P<0.05).These results implied the addition of MHA-Zn(90 mg/kg)can improve production performances,meat performances of broilers in the LP diet,reach a level close to normal protein diet while reducing feed costs and nitrogen excretion.And 90mg/kg of MHA-Zn in LP diet group improved apparent nutrients digestibility,intestinal histomorphology,the beneficial flora of cecum and gene expression related to ileal and jejunal absorption.This study provides a theoretical foundation for the future promotion of low-protein diet technology for broilers with regard to organic zinc nutritional criteria and promotes the development of environmentally friendly broilers farming with low nitrogen excretion.