Effect Of Dietary Triiodothyronine Supplementation On Growth And Protein Retention Of Black-bone Chickens

The present study investingated the effect of dietary T3 supplementation on growth and protein retention of black-bone chickens,and the carry-over effect of dietary T3 supplementation. A total of 640 black-bone birds were assigned to 4 treatments( I II III IV) with 4 replicates which conclued 40 birds. The control birds( I ) was fed basal diet and other birds were fed basal diet supplemented with 0.1( II )N 0.3(III) and 0.5(IV)mg T3/kg diet respectively. All birds consumed feed and water ad libitum. The whole period was separated into early period (0-4 week) and late period(5-8 week). At 5th week, every replicate was separated into two group(A group and B group) again , the birds of group A was fed basal diet, birds of group B continue fed basal diet supplemented with T3. Protein deposition in leg and breast muscle, growth performance, and serum T3, T4, TSH, GH and Ins were measured at 2th, 4th, 6th, 8th week.At the end of trial,a metabolize experiment was carried to measure nitrogen metabolize efficiency.The results showed that dietary supplemented with 0.1 mgT3/kg improved accumulative growth, average body-weight gain and relative growth ratio before 6th-week, and retarded them after 6th-week.Supplemented with 0.5mgT3/kg depressed growth of black-bone chickens during whole period. In 7-8week, added T3 to diet retarded performance;while withdrawed T3 to diet performance recovered (P>0.05). Nitrogen metabolize efficiency was significantly decreased by dietary T3 supplementation. Protein retention in leg and breast muscle was significantly affected by supplemented with 0.1mgT3/kg at 2nd-week. During 7-8 weeks, protein retention was decreased in leg muscle and increased in breast(P>0.05) by treated with T3 ,and detail, B group of three treated group was lower 12.13%, 5.47%, 1.30% in leg muscle and higher 15.38%,7.82%, 3.42% in breast muscle respectively than that of A group.T3 concentration in serum significantly increased,T4 concentration inserum significantly decreased with T3 added to diet at 2nd-week, and T3 , T4 concentration significantly decreased at 4th-week.At 6th-week, T3 concentration of three A group was 2.37,32.33,38.00 times of that of B group respectively. At 8th-week, T3 concentration of A group of three trial groups was 1.68,10.31and 16.00 times of that of B group respectively;while T4 concentration ofA group was higherl8.53%,39.42%,123.23% than that of B group respectively.lt suggested that:1. Dietary T3 supplementation stimulate growth of black-bone chickens before 6th-week,and optimal dose is 0.1mgT3/kg diet;After 6th-week,dietary T3 supplementation retard growth of black-bone chickens;While withdrawed T3 to dietary,growth is recovered. Nitrogen metabolize efficiency is significantly decreased by dietary T3 supplementation at 8th-week, and correlation between nitrogen metabolize efficiency and T3 is y=13.164x+59.109 (R2=0.8267).2. Protein retention in leg and breast muscle can be promoted by dietary T3 supplementation before 6th-week,and appropriate dose is 0.1mg/kg.3. At 2nd-week, T3 concentration in serum is significantly increased, while T4 concentration in serum is significantly decreased when T3 is added to diet. After 2nd-week, both T3 and T4 concentration in serum is significantly decreased by dietary T3 supplementation during late period, and increased while withdrawed T3 to diet. GH andTSH concentration has no significantly change in whole period.