Bioefficacy And Toxicity Of Methionine With Different Optical Activity In Pekin Ducks

Four experiments were conducted in this study to investigate the effects of dietary methionine on growth performance,carcass quality and blood parameters of Beijing ducks,to evaluate the efficiencies of L-methionine?LM?relative to DL-methionine?DLM?,to determine the methionine requirement and maximum safe level?MSL?and to study the effects of excess methionine on transcriptom of liver by RNA-seq.Our objective was to provide a theoretical basis for the use of crystal methionine in meat ducks.Experiment 1 was carried out to evaluate the relative bioavailability of LM compared to DLM for Bejing ducks from 1 to 21 days of age fed by corn-peanut meal diets.There were 15 treatments containing a control diet?Met 0.29%,ME 12.56MJ/Kg,CP 22.15%?and control diet supplemented with crystal LM or DLM according to 7 supplemental levels?0.03,0.06,0.10,0.14,0.19,0.24 and 0.29%?.A total of 720 1-day-old ducks were randomly allotted to 15 groups with 8 replicate pens per group and 6ducks per replicate.The trial lasted for 21 days.The results showed as follows:Compared with the control group,optimal addition of methionine in diets could improve average body weight?ABW?,average daily weight gain?ADG?,average daily feed intake?ADFI?,and leg meat rate?P<0.05?.The ABW and ADG were increased firstly and then decreased with the increase of Met supplemental level for ducks fed diets supplemented with LM,while the ABW and ADG were increased and then stabilized for ducks fed diets supplemented with DLM.The L-Met and DL-Met requirement for maximum ADG of ducks from 1 to 21 days of age were 0.46%,0.54%,respectively.The requirement of LM is less than DLM.According to growth data of groups with methionine levels of 0.29,0.32,0.35,0.39,0.43 and0.48%,the bio-efficacy of LM relative to DLM was 134%for ADG by the linear ratio-slope regression.Experiment 2 was carried out to estimate the relative bioavailability of LM compared to DLM for Beijing ducks from 15 to 35 days of age fed by corn-peanut meal diets.There were 15 treatments containing a control diet?Met 0.22%,ME 12.75MJ/Kg,CP 18.18%?and control diet supplemented with crystal LM or DLM according to 7 supplemental levels?0.03,0.06,0.09,0.13,0.17,0.22 and 0.27%?.A total of 720 15-day-old ducks were randomly allotted to 15 groups with 6 replicate pens per group and 8ducks per replicate.The trial lasted for 21 days.The results showed as follows:Compared with the control group,optimal addition of methionine in diets could improve growth performance,the length of the left fourth primary wing feather?P<0.05?and could improve breast meat rate?0.05<P<0.10?.The L-Met and DL-Met requirement for maximum ADG of ducks from 15 to 35 days of age were 0.41%,0.37%,respectively.However,there was no significant differance between the requirement of LM and DLM.According to growth data of groups with methionine levels less than requirement?supplemental levels were 0.00,0.03,0.06,0.09,0.13 and 0.17%?,the bio-efficacy of LM relative to DLM was 125%for ADG by the linear ratio-slope regression.Experiment 3 was conducted to estimate the relative bioavailability of excess LM compared to excess DLM for Beijing ducks from 8 to 28 days of age fed by corn-soybean meal diets.There were 11treatments containing a methionine-adequate control diet?Met 0.47%,ME 12.03MJ/Kg,CP 18.99%?and control diet supplemented with crystal LM or DLM according to 5 supplemental levels?0.25,0.50,0.75,1.00 and 1.25%?.A total of 492 8-day-old ducks were randomly allotted to 11 groups with 7replicate pens per group and 6 ducks per replicate.The trial lasted for 21 days.The results showed as follows:Compared with the control group,excess methionine in diets could decrease the ABW,ADG,F/G,breast meat rate,and adnominal fat?P<0.05?.Plasma homocysteine?Hcy?,glutamic-pyruvic transaminase?ALT?,total bilirubin?TBIL?,lactic dehydrogenase?LDH?,mean corpuscular volume?MCV?and red blood cells volume distribution width?RDW?were increased with the increase of methionine level in diet?P<0.05?,while decreased hemoglobin?Hb?,mean corpuscular hemoglobin?MCH?and mean corpuscular hemoglobin concentration?MCHC?.Meanwhile,the decrease trendency of red blood cell count?RBC?was observed?0.50<P<0.10?.According to broken-line model,the MSL of DLM and LM for ADG were 0.89%,0.86%,respectively.There was no significant differance between the MSL of LM and DLM.According to the linear ratio-slope regression,the relative bio-efficacy of LM compared to DLM for ADF and ADFI were 100%,102%,respectively.Experiment 4 was conducted to study molecular mechanisms of methionine toxcity on Beijing ducks.Three ducks were selected from basal diets group?0.47%?and excess methionine in diets group?1.72%?,respectively.Liver were collected for RNA extraction,sequencing and data analysis.The results showed as follows:According to the criteria of|log₂Fold Change|?0.58 and P-value?0.05,there were 1082 differencially expressed genes,which were mainly related to lipid metabolism,energy metabolism and mitochondria apoptosis;There were 467 up-regulation genes and 615 down-regulation genes;Significantly enriched GO term involved in the biological process of lipid metabolism,immune response and mitochondria apoptosis;Significantly enriched KEGG pathway involved in the pathway of calcium signaling pathway,cytokine-cytokine receptor interaction,PPAR signaling pathway and so on.In conclusion,optimal levels of L-Met and DL-Met in diets was beneficial to growth performance and carcass quality of Beijing ducks from 1²1 or 15³5 days of age.However,excess L-Met and DL-Met in diets would lead to depression of growth,liver lesion and anemia.The bioavailibility of LM was higher than DLM when the methionine levels in diets could promote growth of Beijing ducks.The bioavailibility of LM equal to DLM when the methionine levels in diets could depress growth of Beijing ducks.Excess methionine in diets mainly affect mRNAs related to lipid metabolism and active signaling pathways associated with lipid metabolism.