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The Influence of Dietary Energy, Protein, and Copper Levels on the Sulphur Amino Acid Requirements of Broiler Chickens
Dissertation Abstract:
Three experiments were conducted using male broiler chicks to determine the influence of dietary metabolizable energy (ME), crude protein (CP), and copper (Cu) levels on the total sulphur amino acid (TSAA) requirement of broilers both during the starter (0-3 wk) and the grower periods (4-6 wk) reared in the tropics. The parameters used in evaluating the TSAA requirements in all the experiments were body weight gain, feed-gain ratio, and carcass composition.
In the first experiment, two factorial arrangements of three ME levels (3,000; 3,200; and 3.400 kcal/kg) x four level of TSAA (0.73, 0.83, 0.93. and 1.03%) and the same three ME levels (3,000; 3,200; and 3,400 kcal/kg) x four levels of TSAA (0.65, 0.72, 0.79, and 0.86%) were used for the starter and the grower periods, respectively. The results showed significant differences (P<0.05) in body weight gain and feed-gain ratio of the broilers with increasing dietary TSAA levels both in the starter and grower periods. There were no significant interaction (P<0.05) between dietary ME and TSAA levels for the performance, with the exception of feed intake of stater broilers. For the starter period, a TSAA of 0.93 percent produced the best performance regardless of energy levels while for the grower period, the requirement of TSAA at both 0.79 and 0.86 percent were suggested. Results further showed that dietary energy levels had no effect on the TSAA requirement of the broilers.
In the second experiment, two factorial arrangements of four CP levels (16, 18, 20, and 23%) x three levels of TSAA (0.83, 0.93, and 1.03%) and three CP levels (16, 18, and 20%) x three levels of TSAA (0. 72, 0.79, and 0.86%) were examined for the starter and grower periods, respectively. The results showed significant intluence (P<0.05) of dietary CP levels on body weight gain and feed-gain ratio in both starter and grower periods. No significant interaction between dietary CP and TSAA levels was noted for the broilers· performance. The results suggested that the TSAA requirement of broiler chickens during the starter period was 0.93 percent and 0. 79-0.86 percent during the grower period. However, the dietary protein levels did not affect the TSAA requirement per unit of diet.
In the third experiment, studies were also carried out with two factorial arrangements of four Cu levels (0, 125, 250, and 375 mg/kg) x three TSAA levels (0.73, 0.83, and 0.93%) The same levels of Cu (0, 125, 250, and 375 mg/kg) x three levels of TSAA (0. 72, 0.79, and 0.86%) were used during the starter and grower periods, respectively. Results indicated that supplementation of Cu at the 375 mg/kg level significantly decreased (P<0.05) feed intake of chicken in both growing periods. This resulted in significant reduction (P<0.05) of the growth rate and interference with the TSAA requirement of the starter broilers. However, the resu lts showed that in grower broilers, Cu had no effect at the levels used to increase the TSAA requirement of chicken. Dietary copper had no influence on carcass, meat, and skin composition of the broilers.
Results of this study indicated that under tropical conditions the National Research Council (NCR, 1984) recommendation for TSAA requirements of 0.93 percent for starter broilers is adequate. However, NCR's recommended level of 0.72 percent for grower broilers is less than the level of 0.79-0.86 percent suggested based on the results of this study. Moreover, the TSAA requirements of broilers per unit of diet were not affected by dietary ME and CP levels. Although the dietary copper level examined interfered with the TSAA requirements of starter broilers, futher analysis showed it had no effect on the grower broilers.