Research On Optimal Threonine Requirement Of Commercial Laying Hens In Low Energy Diets

This study was conducted to determine the influence of different dietarythreonine levels on the production performance, egg quality, N-retention and truedigestibility of amino acid of commercial laying hens in the peak period, and primarydiscussion for ideal amino acid pattern of laying hens in this production phase wasprogressed.Experiment1: Effect of different threonine levels on production performance of layinghens in low energy diets.This study was conducted to evaluate the influence of different threonine levels oflow energy diets on the production performance of commercial laying hens in the peakperiod. Six hundred Hy-Line Variety Brown hens were randomly divided into fivegroups with five replicates per group and24hens per replicate. The basal diet wascorn-peanut meal. Metabolizable energy level was10.89MJ/kg (2600Kcal/kg) andthere were five different threonine levels (0.45%,0.50%,0.55%,0.60%,0.65%).The results showed that:(1) Different threonine levels of low energy diets hadsignificant effects on egg production rate and egg mass (P <0.05).0.60%threoninelevel group was the highest of all and was significantly higher than0.50%group(P <0.05), but there were no significant difference among the other groups (P>0.05) foregg production rate.0.45%group was the highest of all and0.60%group took thesecond place, and0.50%group was the lowest of all for egg mass. Both0.45%groupand0.60%group were significantly higher than0.50%group (P <0.05), but therewere no significant difference among the other groups (P>0.05).(2) Differentthreonine levels of low energy diet had no significant effects on feed intake, egg weight,feed consumed/egg mass, egg broken ratio and daily gain (P>0.05).(3)0.45%grouphad the lowest feed cost of producing100kg eggs of all groups. It could be saved16.91,13.54,3.56and13.54yuan respectively than the other groups. Taking the aboveproduction performance and economic benefit into consideration, we suggested that0.45%threonine level appear adequate for Hy-Line Variety Brown hens in the peakperiod (26～34week) when the metabolizable energy was10.89MJ/kg (2600Kcal/kg),or total threonine requirement was547mg/hen/d. Experiment2: Effect of different threonine levels on egg quality in low energy diets.This study was conducted to determine the influence of different dietary threoninelevels on the egg quality of commercial laying hens in the peak period. Experimentaldesign was the same as experiment1. At the end of feeding experiment, three eggswere collected randomly from each replicate to measure egg quality. The resultsshowed that: threonine levels of diets, ranging from0.45%to0.65%, had nosignificant effects on egg shape index, eggshell strength, protein height, yolk color andHaugh unit (P>0.05). These showed that different dietary threonine levels had noeffects on egg quality.Experiment3: Effect of different threonine level on N-retention and true digestibility ofamino acid of laying hens in low energy diets.This study was conducted to evaluate the influence of different dietary threoninelevels on N-retention and true digestibility of amino acid of commercial laying hens inthe peak period. At the end of feeding experiment, four body condition consistent hensof per replicate were selected for metabolic test. Five body condition consistent adultroosters were selected to determine endogenous nitrogen and endogenous amino acid.The results showed that:(1) Different threonine levels in low energy diets hadsignificant effects on N-excretion, N-retention and N-retention rate (P <0.05).0.45%threonine level group had the lowest N-excretion but the highest N-retention andN-retention rate.0.45%group was extremely significant lower than0.60%group forN-excretion (P <0.01).0.45%group was significant higher than0.65%group for N-retention and N-retention rate (P <0.05), as well as there were no significant differencewith the other groups (P>0.05). There were no significant difference on nitrogen intakeand daily nitrogen balance among the groups (P>0.05).(2) Different threonine levels inlow energy diet had extremely significant effects on true digestibility of threonine(P <0.01) and had significant effect on true digestibility of crude protein, aspartate,glutamic acid, cystine, tyrosine, histidine and arginine (P <0.05), but had no significanteffects on true digestibility of methionine, lysine, serine, glycine, alanine, valine,isoleucine, leucine, phenylalanine, proline and tryptophan (P>0.05). That is to say,0.45%threonine level of diet, or total threonine requirement was547mg/hen/d, ordigestible threonine requirement was470mg/hen/d, can improve daily nitrogen balance,and increase N-retention and N-retention rate when the metabolizable energy was10.89MJ/kg (2600Kcal/kg). Furthermore, different threonine levels of diets hadinfluence on utilization rate of crude protein, threonine, aspartate, glutamic acid, cystine, tyrosine, histidine and arginine.Experiment4: Study on the ideal amino acid pattern of laying hens in the peak period.According to analyse the amino acid pattern of maintenance, weight gain and egglaying, we obtained the ideal amino acid pattern of allocation proportion of N-retentionto weight the three-part of amino acid pattern of laying hens. Assumed the lysine is100,the ideal amino acid pattern was as follow: Lys: Met: Cys: Trp: Thr: Ile: Leu: Phe: Tyr:Val: Arg: His=100:54:51:22:72:88:121:72:58:102:91:63.