| Summary: | 碩士 === 國立臺灣大學 === 畜產學研究所 === 92 === The purpose of this study was to determine the different levels of zinc and tryptophan on growth performance and the interaction of zinc and tryptophan in broilers for improving the chicken production efficiency. The experiment was a 3×3 factorial design. The diets contained three levels of zinc and three levels of tryptophan, respectively with low, medium, and high levels. The medium diet was optimal as recommended by NRC (1994). In experiment 1, casein, corn grain, and gelatin were used as basal components in the diet. In experiments 2, 3 and 4, casein was replaced by dehulled soybean meal. The zinc and tryptophan content of basal diet were 19.3 ppm and 0.15%, respectively in experiment 1, while in experiments 2 to 4, there were 20.1 ppm and 0.13%. In the medium and high levels, 40 and 80 ppm zinc and tryptophan 0.15 and 0.3% were, respectively added to the basal diet. Feed and water were provided ad libitum during the experimental period of 3 weeks. At the 15th day after commencement of the experiment, feces were collected for 3 days to determine the apparent metabolizability of zinc. At the termination of the experimrnts, blood samples were taken by cardiac puncture for measuring serum zinc and tryptophan concentration. During the experimental period, feather development of broilers was recorded. After chicks were sacrificed by cervical dislocation, left tibia was removed for determination of zinc content.
The results indicated that chicks fed low tryptophan diet had significantly less weight gain and feed intake than those fed adequate or high tryptophan diets. The weight gain of broiler on low zinc groups was inconsistent. There was no interaction between dietary zinc and tryptophan. Feed efficiency was not significantly changed in chicks fed different levels of zinc and tryptophan. Both zinc apparent metabolizability and serum zinc content were significantly affected by dietary zinc levels. Chicks fed the high zinc diet had significantly lower apparent metabolizability and higher serum zinc content than chicks fed medium or low zinc diets. Serum tryptophan was lower in chicks fed low tryptophan diet. The tibia weight and its zinc concentration were affected by dietary zinc levels. Also zinc and tryptophan levels affected feather development of three-week old chicks. When chicks were fed low zinc or low tryptophan diets, feather development was poorer than chicks fed adequate or high zinc and tryptophan diets. The tryptophan levels in the diet could not affect the apparent metabolizability of zinc in broiler chicks.
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