| In order to investigate the interaction between methionine and cystine of early ducklings,two experiments were carried out.In experiment 1,twenty male adult Pekin ducklings were used to measure the true digestibility of methionine and cystine in the low sulfur amino acid dietten ducks were tube-fed with free-protein diets and the other ten ones were tube-fed with low sulfur amino acid diet.In experiment 2,A 4x5 factorial arrangement of treatment was used which include five levels of methionine (0.285%, 0.385%, 0.485%, 0.585%,0.685%) and four levels of cystine (0.325%,0.406%, 0.487%, 0.568%).Low sulfur amino acid diet used in experiment 1 was use as basic diet in experimentDifferent levels of methionine and cystine was added to it to make up experimental diets.eight hundreds one-day male Pkin ducklings were used in this experiment. Four replicates of ten ducklings were assigned to each of the twenty experimental diets.these ducklings were reared for twenty-one days, feed and water were provided ad libitum.M 14-day and 24-day,ducklings were weighed to measure the growth performance and then eight ones of each treatment were blooded and slaughtered to measure the growth of some tissues and organs and some biochemical indexes in plasma.The result of two experiments were as follow:1.The digestibility of methionine and cystine in the experimental basic diet of early Pekin ducklingsThe digestibility of methionine and cystine in the experimental basic diet of early Pekin ducklings were 93.89% and 88.25% respectively(air dry matter).SO,the digestive methionine and cystine of this diet were 0.268%,0.287% respectively(air dry matter). 2.Effects of methionioe and cystine on the growth performance of early Pekin ducklings Methionine had a significant effect on weight gain and feed intake at 14-day and 21-day(P<0.05).At 14-day,weight gain and feed intake rose and failed as the level of methionine was raised,but the quadratic response was not significant(P>0.05).And the quadratic response of weight gain was significant at 21-day(P<0.05).Methionine had no significant effect on the feed conversion efficiency at 14-day,but high level of methionine(0.585%,0.685%) improved it significantly(P<0.05) at 21-day.Cystine had no significant effect on weight gain,feed intake, feed conversion efficiency at 14-day and 21-day,but high level of cystine(0.568%) suppressed the weight gain and feed intake at 14-day(P>0.05) and the suppressions were significant at 21-day(P<0.05) 3.Effects of methionine and cystine on the growth of some tissues and organs of early Pekin ducklingsMethionine raised the leg meat yield and its percentage of live weight of 14-day and 21-day Peckin duckling(P<0.05) and the breast meat and its percentage of live weight of 21-day were improved significantly(P<0.05).but Methionine had no significant effect on the weight of heart,liver,and gizzard and their percentage of live weight of 14-day and 21-day Pekin duckling(P>0.05).Cystine had no significant effect on the weight of leg meat, heart,liver,and gizzard and their percentage of live weight of 14-day and 21-day Pekin duckling(P>0.05) and it also had no significant effect on the weight of breast meat and its percentage of live weight of 21-day Pekin duckling(P>0.05).4.Effects of methionine and cystine on some biochemical indexes of some tissues and organs of early Pekin ducklingsMethionine had significant effect on uric acid,homocystein in plasma of 14-day and 21-day Pekin duckling(P<0.05),but it had no significant effect on total protein in plasma at 14-day and 21-day(P>0.05).high level of methionine raised creatine in duckling plasma at 14-day(P<0.05),but the response was not significant at 21-day(P>0.05).Uric acid in plasma failed and rose as th level of methionine was raised and quadratic response was significant at 14-day(P<0.05),but the response was not significant(P>0.05).Homocysteine in plasma was increasing linearly at 14-day as the level of methionine was raised (P<0.05) but it was not significant at 21-day.Cystin...
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