Estimation Of Optimum Requirements For Major Essential Amino Acids In Low-protein,Amino Acid-supplemented Diets For Laying Hens

Regarding the imbalanced nutrition of low-protein,amino acid-supplemented diets,a study was conducted to assess the requirement of laying hens(33 to 41 day of age)for 4essential amino acids and their appropriate proportion,and determine the optimum level of lysine(Lys)under different extents of decreasing dietary crude protein(CP)concentration in older laying hens(70 to 78 day of age),with the goal to clarify the ideal amino acid profile for laying fowl and the association of essential amino acids(EAA)with non-essential amino acids(NEAA),providing new ideas and methods for the scientific formulation of low-protein,amino acid-supplemented diets.In trial 1,4 separate experiments were conducted with Hy-Line Brown hens to determine the ideal ratio of Met,Met+Cys,Trp,and Arg relativeto Lys for maximal egg mass.Experiments were conducted simultaneously and were each designed as a randomized complete block design with 30 experimental units(each consisting of 3 cage with 3 hens)and5 dietary treatments.The 20 assay diets were made from a common basal diet(2,987 kcal/kg of ME;10% CP),formulated using corn and soybean meal.The true digestible amino acid contents in the basal diet were determined using the precision-fed assay with adult cecectomized roosters.Crystalline L-Lys·HCl,DL-Met,L-Trp and L-Arg(considered 100%true digestible)were added to the basal diet at the expense of corn starch to make the respective assayed amino acid first limitingand to yield 5 graded inclusions of the assayed amino acid.Hens were fed the assay diets from 33 to 41 wk of age,with the first 1 wk considered a depletion period.Egg production was recorded daily and egg weight was determined weekly on eggs collected over 48 h;egg mass was calculated as egg production ×egg weight.The requirement for each amino acid was determined using the broken-line regression method.Consumption of Arg did not affect egg mass,thus a requirement could not be determined.The true digestible amino acid requirements used to calculate the ideal amino acid ratio for maximum egg mass were 539 mg/d of Lys,254 mg/d of Met,507 mg/d of Met+Cys,and 122 mg/d of Trp.The ideal amino acid ratio for maximum egg mass was Met47%,Met+Cys 95% and Trp 23% on a truedigestible basis relative to Lys.In trial 2,the optimum level of Lys in low-protein,amino acid-supplemented diets was investigated.A total of 540 Hy-line Brown laying hens at the age of 70 week were randomly divided into 10 groups,each with 6 replicates of 9 birds.The first group was the control,with hens fed a conventional diet(16% CP).A completely randomized experimental design with a3 × 3 factorial arrangement(dietary CP and Lys levels)was applied to the remaining groups.Dietary CP contents were 14%,12% and 10%,and dietary Lys levels were 0.76%,0.90% and1.04%.Except Lys,the remaining EAA of the assay diet was fortified by the addition of crystalline amino acids(synthetic amino acids)to the same level as the control.The preliminary trial period was 1 week,and the formal test lasted for 8 weeks.It was found that supplemental Lys of low(0.76%)or medium(0.90%)dose maintained the normal laying rate,egg mass and feed to egg ratio,with the reduction of dietary CP by 2 percentage points(14%CP).When dietaty CP content was reduced by 4 percentage points to 12%,a high dose of supplemental Lys(1.04%)was needed to maintain the normal production performance of laying hens.As the dietary CP level was further decreased(10% CP),laying performance became worse with the current level of Lys supplementation.These results indicated that NEAA(s)are decreased with the reducing level of dietary CP,so the supply of EAA,e.g.Lys,should be increased to maintain the normal production performance.