An experiment was conducted to evaluate the effects of D-Thyroxine (T4) on compensatory growth of broiler chickens. The experiment was designed in a 2×5 factorial with 5 replicate pens of 12 male or female chicks each. Six hundred male and/or female day-old chicks were weighed and randomly allocated to 5 treatment groups of each sex. Five treatments including: A control (C, with no feed restriction and T4) and 4 restricted groups which were fed a mixture of 50:50 rice hulls and a starter diet with supplementation of trace minerals and vitamins from 4-11 days of age. All groups were fed similar diets from 11-56 days of age, with the exception that the diets of 4 restricted groups R0, R1, R2 and R3 were supplemented with 0, 1, 2 and 3 ppm T4 from 11-28 day, respectively. The lowered LBW of` R0 birds was compensated at 42 day, whereas the LBW of R1, R2 and R3 treated birds was decreased as the level of T4 was increased. The LBW of R1 and R2 treated birds were similar at 49 day and this was lower than (p<0.05) the C and R0 birds. Among the T4 treated birds, only the R1 birds could complete a compensatory growth at 56 day. The LBW of R0 birds was numerically higher than of C birds at 56 day. The FI of birds with the exclusion of ground rice hulls was not different (p>0.05) among the C, R0 and R1 birds during 1-42 or 49 and/or 56 day but this FI value was significantly higher than obtained from R2 and R3 birds. The FCR of R0 birds was numerically better than of C or T4 treated birds, whereas all T4 treated birds exhibited a poorer FCR during 1-42 or 49 and/or 56 day. The performance parameters in male chicks were significantly better than of female chicks. Carcass fat content of the R0 treated birds was significantly lower than that of control or other treated birds (p<0.05). Carcass fat content of male chicks was lower than (p<0.05) that of female chicks. AFP of the R0 birds was lower than (p<0.05) that of control or T4 treated birds at 49 day, whereas all birds had a similar abdominal fat at 56 day. Therefore, compensatory growth in broiler chicks can be achieved at 42 day with diet dilution in early of life. The dietary T4 depressed performance characteristics. Serum Thyroxine was increased by feed restriction and reached to normal level when birds were re-fed.

Keywords