Effect Of Amino Acid Supplementation In Low Protein Diets On Performance,Gut Health And Nitrogen Balance Of Weaned Pigs

Many investigators reported that reducing dietary crude protein(CP)level while proper balancing with crystalline amino acids(AA)did not affect growth performance but decreased diarrhea incidence of weaned pigs.However,a majority of previous studies dealing with low CP diets mainly focused on different levels of dietary CP and balanced limiting AA on performance or N retention of pigs,but information about the effects of AA supplementation in low CP diets on performance or N retention of weaned pigs are scarce.Some researchers observed that increasing Lys and other essential AA(EAA)from deficient to adequate levels has shown to improve ADG and FCR.Furthermore,compared NRC(2012)with NRC(1998),we could find that the AA requirements of swine in current years were higher than before.But,these data were on the basis of normal CP diets,it is not proper apply to low CP diets.Therefore,the objectives of the present experiments were to evaluate the effect of reducing dietary CP content and increasing AA supplementation on weaned pigs,and to determine the optimal EAA level of 8 to 20 kg weaned pigs when fed with low CP diet.Experiment 1 Effect of Supplemented Varied Amino Acid Levels in Low Protein Diets on Performance and Gut Health of Weaned PigletsIn order to measure the optimal EAA level of weaned pigs fed with low CP diet,one hundred and forty-four weaning pigs with 8.10 ± 0.48 kg were randomly assigned to 1 of 6 dietary treatments with 6 pens per treatment and 4 pigs per pen.Diet 1 was the control diet contained 20%CP with 100%essential amino acids(EAA)(i.c.100%of the NRC(2012)recommendation of EAA for 11 to 25 kg pigs).Diets 2 to 6 contained 18.5%CP but varied in EAA level(80,90,100,1 10 and 120%of EAA level recommended by the NRC,2012).The trial lasted for 28 d,on d 0,14 and d 28,blood samples were collected from 6 randomly selected pigs in each treatment after fasting for overnight via anterior vena cava puncture into glass tubes without anticoagulant.On d 28 one piglet chosen from each replicate was killed and sampled.The results were as follows:(1)The performance of pigs was not different when dietary CP reduced from 20 to 18.5%with similar EAA level(P>0.05),but reduced the diarrhea incidence of pigs significantly(P<0.05).However,there were significantly effect on performance and SUN when dietary supplemented varied EAA levels.With dietary EAA level increasing,FCR(linear,P<0.01;quadratic,P<0.01),ADG(linear,P<0.01;quadratic,P = 0.02)increased;but SUN decreased(quadratic,P = 0.02)during the overall experiment period.Using curvilinear plateau and two-slope broken-line model,the optimal EAA level of 8 to 20 kg weaned pigs fed with low CP diet(18.5%CP)was estimated as 103.5%,102.0%and 108.8%EAA of NRC(2012)recommendation to optimize ADG,FCR and the minimal SUN,respectively.(2)Both dietary CP reduced from 20 to 18.5%or supplemented varied EAA levels in low CP diets were not affected the development of viscera and small intestinal morphology,the concentrations of serum TP,GPT,GOTand IgG,the content of immunoglobulin and digestive enzyme activities in jejunum of weaned pigs(P>0.05).However,serum ALB increased(linear,P = 0.02)and the content of protein in ileum increased(linear,P<0.01),in duodenum tended increased(quadratic,P = 0.06),but the activities of sucrose in jejunum tended decreased(quadratic,P = 0.08)as EAA levels increased.(3)Increasing with EAA levels,both increased the mRNA expression of CAT1(linear,P<0.01)and IGF-1(quadratic,P = 0.03),the serum concentrations of Lys(linear,P<0.01)and Val(quadratic,P<0.01),however,the serum concentrations of His declined(linear,P<0.01;quadratic,P<0.01)and Phe declined linearly(P<0.01).In addition,no differences were observed among other essential amino acids(P>0.05).(4)Reducing dietary CP content is an effective strategy to minimize the concentrations of NH3-N and VFA,and promote the production of beneficial bacterium in hindgut of weaned pigs.Furthermore,the content of NH3-N decreased(quadratic,P0.03),the populations of Lactobacillus,Bifidobacteriwm,Bacillus increased(linear,P<0.01),and the concentration of butyric acid increased(quadratic,P = 0.04)as EAA levels increased of weaned pigs fed with low CP diets.These results indicated that EAA supplementation higher than the recommendation of NRC(2012)is beneficial for increasing the efficiency of dietary N,promoting the synthesis of protein of weaned pigs,reducing the undigested proteins in hindgut,enhancing the formation of beneficial bacteria,and decreasing the generation of harmful metabolites.Experiment 2 Effect of Supplemented Varied Amino Acid Levels in Low Protein Diets on Nitrogen Balance of Weaned PigletsThe aim of the trail is to evaluate the effect of supplemented varied AA levels on nitrogen balance of weaned pigs fed with low CP diet.Eighteen pigs with 11.94 ± 0.31 kg were used in a 12-d N-balance trial.Pigs were randomly assigned to 1 of 3 dietary treatments,1)20%CP diet with 100%EAA,2)18.5%CP diet with 100%EAA,3)18.5%CP diet with 110%EAA.Pigs were allowed to have a 7-d adaptation period in the metabolism crates,meal regimen and experimental diets,and a 5-d period of quantitative collection of feces and urine.The results were as follows:(I)Compared with the 20%CP diet,total N excretions of pigs fed 18.5%CP diet with 100%EAA reduced 11.2%.(2)The total N excretions was further decreased when pigs fed 18.5%CP diet with 110%EAA compared with 100%balanced EAA.Furthermore,we found that pigs fed 18.5%CP with 110%balanced EAA had a greater ATTD of GE,CP and most essential A A and N retention(%of N intake).It indicated that pigs fed this diet had better AA absorption capacity.These results suggested that EAA supplementation higher than the recommendation of NRC(2012)could enhance the efficiency of dietary protein.Collectively,the results from the experiments on performance and nitrogen,showed that reducing dietary CP from 20 to 18.5%while balancing to meet the requirements of essential AAs did not affect the growth performance of 8 to 20 kg pigs,but significantly decreased the diarrhea incidence rate and total N excretion.Increasing with the EAA levels,increased the efficiency of dietary protein,and promoted the synthesis of protein of weaned pigs,reduced the undigested proteins in hindgut,enhanced the formation of beneficial bacteria,and decreased the generation of harmful metabolites.The optimal EAA level for 8 to 20 kg pigs fed 18.5%CP diet was estimated as 105%EAA of the NRC(2012)recommendation,which is equivalent to 1.29%SID Lys.