| Environmental pollution and the shortage of protein feedstuffs are two major problems in animal production,which can be alleviated by the utilization of low protein diet.However,there are still some problems in the research and application of low protein diets.For example,reducing the dietary protein level will result in fattening of carcasses and the dietary protein level decreasing by 4%,which will have inconsistent effects on the growth performance of pigs.Therefore,this study was conducted to study the effects of different net energy levels of low protein diets on growth performance and nitrogen excretion of growing-finishing pigs,and then determined the different amino acid balanced patterns of low-protein diets on growth performance,carcass characteristics,nitrogenexcretion,and colonic microflora of growing-finishing pigs.This study was divided into two parts: Exp.1 Effect of different net energy levels of low protein diets on growth performance and nitrogen balance of growing-finishing pigsA total 18 barrows(25.00 ± 0.50 kg)and were randomly divided into 3 treatments according to their initial body weight.Test period divided into three phases,25-50 kg,50-75 kg,and 75-105 kg.The three treatments included high protein and high net energy diet,the protein levels and net energy levels in the three phase were 17.04%-15.43%-13.62% and 10.36 MJ/kg-10.36 MJ/kg-10.36 MJ/kg,respectively;low protein and high net energy diet,the three phase of protein levels and net energy levels were 13.78%-12.20%-10.34% and 10.36 MJ/kg-10.36 MJ/kg-10.36 MJ/kg,respectively;low protein and low net energy diet,protein levels and net energy levels in the three phase were 13.51%-12.16%-10.20%,and 9.86 MJ/kg-10.01 MJ/kg-10.01 MJ/kg,respcectiviely.There were balanced 10 essential amino acids in the three treatments.During the 90 days of the trial period,the nitrogen balance test was performed using the total faeces and urine collect test in the last 4 days of each phase.At the 91 st day of the experiment,fasting blood was collected from each pig.The results showed as follows: There was no significant difference in growth performance and apparent digestibility of nutrients among the three treatments at each phase(P> 0.05).The low protein diets with high NE level or low NE level significantly reduced nitrogen intake and nitrogen excretion at each phase(P< 0.05),and also significantly reduced serum urea nitrogen levels,ammonia nitrogen levels and the population of fecal E.coli(P<0.05).Exp.2 Effects of low-protein diets supplemented with different amino acids on growth performance,carcass characteristics,nitrogen balance and colonic microflora of growing-finishing pigsA total 42barrows(25.34 ± 0.39 kg)were randomly assigned to 7 treatments based on their initial body weight.The trial period was 112 days and divided into four phases 25-50 kg,50-75 kg,75-100 kg,and 100-125 kg.The 7 treatments included treatment 1(high protein diet),the NE levels in the four phase were 10.36 MJ/kg andprotein levels were 17.42%-16.01%-14.63%-13.11% and balanced10 EAAs;treatment 2(medium protein diet),according to the NRC2012 recommendation,the net energy levels of the four phase were 10.36 MJ/kg and protein levelswere 15.76%-13.70%-12.40%-10.67%,and 10 EAAs were balanced.The NE levels in the four phase of treatment 3-treatment 7(low protein diet)were 10.06 MJ/kg,and the protein level was decreased by 4% on the basis of treatment 1.And treatment 3 only balanced lysine(Lys),methionine(Met),threonine(Thr)and tryptophan(Trp);treatment 4,5 and 6 were further supplemented with Isoleucine(Ile),Valine(Val)and Ile + Val on the basis of diet 3,respectively;treatment 7 balanced 10 EAAs.The nitrogen balance test was performed using the total faeces and urine collect test in the last 4 days of each phase.The blood sampling and slaughter sampling were performed immediately after the end of the trial.The results showed as follows:With balancing 10 EAAs,a 2% or 4% reduction in dietary protein levels had no significant effecton growth performance,nutrients digestibility,carcass characteristics and meat quality,but significantly reduced nitrogen excretion and slurry ammonia volatilizationat all weight phases(P<0.05),while protein levels decreased by 2% could significantly reduced the abundance of colonic Firmicutes and significantly increase the abundance of Bacteroidetes(P<0.05),the dietary protein level decreased by 4% significantly increased the abundance of colonic Proteobacteria(P<0.05).The dietary protein level was reduced by 4%,supplemented with Lys,Met,Thr,Trp and Val in the 20-50 kg phase significantly improved the ADFI and ADG(P<0.05),and the supplementation with Lys,Met,Thr,Trp and Ile in the 75-100 kg phase and the 100-125 kg phase significantly decreased F/G(P<0.05).Addition of different amino acids had no significant effect on nitrogen excretion and carcass characteristics.Both supplemented with Lys,Thr,Trp,Met,Val and Ile and balanced 10 EAAs increased the population of colonic Firmicutes and significantly decreased the population of colonic Bacteroidetes(P< 0.05).In conclusion,appropriate reduction of the net energy level in the low protein diet had no negative impact on the growth performance of the pigs,however,which improved the carcass characteristics while also significantly reduced nitrogen excretion.Reduction in dietary protein levels by 4 %,addition of different amino acids had no significant effect on nitrogen excretion and carcass characteristics.Balancing with Lys,Met,Thr,Trp and Val was optimal for growth performance during 25-50 kg phase,and balanced with Lys,Met,Thr,Trp and Ile was optimal for growth performance during 75-125 kg phase.Both protein levels and amino acid balanced patterns in low protein diets had no significant effect on diversity of colonic microbes in finishing pigs.With balancing 10 EAAs,protein levels decreased by 2%,which significantly reduced the abundance of colonic Firmicutes and significantly increase the abundance of Bacteroidetes,andthe dietary protein decreased by 4% significantly increased the abundance of colonic Proteobacteria.When dietary protein levels were reduced by 4%,both balancing Lys,Met,Thr,Trp,Val,and Ile and balancing 10 EAAs increased the population of colonic Firmicutes and significantly decreased the population of colonic Bacteroidetes... |
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