| Three phase experiments were conducted to study the effect of dietary lysine, methionine and threonine on growth performances, blood biochemical parameters, apparent metabolism rates and slaughter performance of Yingxiang chickens. The orthogonal 3*3 factorial trial was used to determine the requirements of dietary lysine, methionine and threonine of Yingxiang chickens.In experiment phase 1, 360 one day old Yin Xiang chickens were assigned to 9 treatments with 4 replicas of each treatment. the experimental diets were designed to contain 0.98%, 1.04% and 1.10% lysine; 0.34%, 0.44% , and 0.54% methionine; 0.65%,0.71% and 0.77% threonine,respectively. Chickens were fed designed diets for five weeks from 0 to 5 weeks of age, feed intake, body weight gain were recorded weekly and blood biochemical parameters were measured at 5 weeks of age.The results showed that: (1) Lysine factor had significantly influence on feed/gain(P<0.05); The growth performances in 0.44% methionine level was significantly higher than that in the other levels(P<0.01); Dietary threonine levels had no significant difference on growth performances(p>0.05). (2) In 1.04% lysine level, the activity of alkaline phosphatase and the concentration of total protein in serum were higher than that of the others (P<0.05) ; methionine factor had significantly influence on the concentration of serum urea nitrogen(P<0.05) and total protein(P<0.01).The lowest urea nitrogen and the highest total protein in serum were obtained by 0.54% of dietary methionine level(P<0.05) . Threonine had no significant difference on blood biochemical parameters (p>0.05). Comparing all quotas, under the condition of this experiment, the optimum lysine, methionine, threonine level for 0-5 weeks of Yingxiang chickens can be: 1.04%, 0.44%, 0.77%, respectively.In experiment phase 2, 360 thirty-five days old Yin Xiang chickens were assigned to 9 treatments with 4 replicas of each treatment. the experimental diets were designed to contain 0.87%,0.97% and 1.07% lysine; 0.28%, 0.38% ,and 0.48% methionine; 0.61%,0.73% and 0.85% threonine, respectively. Chicken were fed designed diets for five weeks from 6 to 10 weeks of age, feed intake, body weight gain were recorded weekly and blood biochemical parameters were measured at 10 weeks of age.The results showed that: (1) The factor of methionine and threonine had significantly effect on feed/gain (P<0.05) ; there was no difference in growth performances among the 3 threonine levels(p>0.05). (2) Lysine factor has significantly effect on the concentration of urea nitrogen in serum (P<0.05) .The lowest urea nitrogen in serum was obtained by 0.97% of dietary lysine level; The concentration of total protein in 0.38% methionine level was significantly higher than that of the other levels(P<0.01); The lowest total cholesterol(P<0.01) and protein (P<0.05 ) in serum were obtained by 0.73% dietary threonine level. Comparing all quotas, under the condition of this experiment, the optimum lysine, methionine, threnine level for 6-10 weeks of Yingxiang chickens can be: 0.97%, 0.38%, 0.73%, respectively.In experiment phase 3, 360 seventy days old Yin Xiang chickens were assigned to 9 treatments with 4 replicas of each treatment. the experimental diets were designed to contain 0.66%, 0.76% and 0.86% lysine; 0.20%, 0.34% ,and 0.48% methionine ; 0.47%, 0.57% and 0.67% threonine, respectively. The purpose of this experiment was to determine the requirements of dietary lysine, methionine and threonine of Yingxiang chickens.The results showed that: (1) The factor of lysine and threonine had significantly effect on average daily gain (P<0.05) ; There were significantly difference on feed/gain in lysine and methionine level (P<0.05) . (2) The apparent metabolism rates of lysine(P<0.01), methionine (P<0.05) and threonine (P<0.05 ) increase with increasing lysine, methionine, threonine intake, respectively; threonine factor had significantly effect on protein's apparent metabolism (P<0.05) . (3) The percentage of breast and leg muscle increased with increasing lysine intake (P<0.05 ) . In optimum amino acid level, the abdomen fat percentage decreased significantly (P<0.05) .Comparing all quotas, under the condition of this experiment, the optimum lysine, methionine, threonine level for 11-15 weeks of Yingxiang chicken can be: 0.86%, 0.34%, 0.67%, respectively.
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