Abstract: 【Objective】Dietary methionine(Met) levels for China’s new cultivation of Jinghong laying hens from hatch to the age of 4 weeks were studied.【Method】The trial had adopted one-factor completely random design. Three hundred 1-day-old Jinghong laying hens from a commercial supplier in YuKou poultry were randomly allotted to 5 dietary treatment groups, and the birds in the treatment groups were fed a diet with different dietary methionine levels, respectively, i.e. 0.2% (0.2% Met), 0.3% (0.3% Met), 0.4% (0.4% Met), 0.5% (0.5% Met) and 0.6% (0.6% Met). Each treatment group consisted of 5 replicates with 5 pens per replicate and 12 birds per pen. The experiment lasted for 28 days. On 14th day, after being deprived of feed for 12 h, 2 birds selected randomly from each pen were slaughtered by neck cut and birds were eviscerated manually. The thymus, spleen and bursa of fabricius were weighed and were expressed as a percentage relative to live BW at processing. On 28th day, after being deprived of feed for 12 h, 2 birds selected randomly from each pen were slaughtered by neck cut and birds were eviscerated manually. The immune organs and digestive organs were weighed and were expressed as a percentage relative to live BW at processing.【Result】No significant differences were found in average daily feed intake (P＞0.05), but the average daily gain was significantly different (P＜0.05), and the birds in 0.4% Met group showed the maximum value with 8.31 g•d-1 and significantly higher than 0.2%, 0.5% and 0.6% Met groups (P＜0.05), with a quadratic curve of a rising trend. Besides, feed/gain ratios were also significantly affected (P＜0.05), and the 0.5% Met group was the best (2.13:1) and significantly lower than 0.2% and 0.3% Met groups (P＜0.05), with a quadratic curve of reducing trend. Body weight was significantly affected (P＜0.05), and the 0.4% Met group was the best (268.70 g) and significantly higher than 0.2%, 0.5% and 0.6% Met groups (P＜0.05), with a quadratic curve of rising trend. Community evenness also showed a tendency of a quadratic curve of rising, the 0.5%Met group (85.19%) was significantly higher than the other groups (P＜0.05). By the end of 2nd week, no-significant influence on the relative weights of the thymus and bursa of fabricius (P＞0.05) was found among different groups. There was a significant impact on the relative weights of the spleen (P＜0.05), the 0.4% Met group reached the maximum. By the end of the 4th week, the relative weights of the thymus, spleen and bursa of fabricius showed a significant positive correlation (P＜0.05) with dietary Met levels and all values had a rise-fall tendency. The relative weights of the spleen and bursa of fabricius in 0.4% Met group were the largest; the thymus index in 0.5% Met group was the largest. No significant differences were found in pancreas index and the relative lengths of the duodenum (P＞0.05), but the relative weights of the duodenum, jejunum and ileumor or the relative lengths of the jejunum and ileum were significantly different (P＜0.05). With the increase of methionine, except the relative weights of pancreas which showed a rise-fall tendency, the relative weights of the duodenum, jejunum and ileumor or the relative lengths of the jejunum and ileum had shown a fall-rise tendency. The relative weights of the duodenum in 0.3% Met group were significantly lower than 0.2%, 0.5% and 0.6% Met groups (P＜0.05). The relative weights of the jejunum in 0.4% Met group were significantly lower than other Met groups (P＜0.05). The relative lengths of the jejunum in 0.5% Met group were significantly lower than 0.2%, 0.3% and 0.6% Met groups (P＜0.05). The relative weights of the ileumor in 0.4% Met group were significantly lower than 0.6% Met group (P＜0.05). The relative lengths of the ileumor in 0.3% Met group were significantly lower than 0.2%, 0.5% and 0.6% Met groups (P＜0.05). There were significant differences among groups in the level of serum urea nitrogen, uric acid and alkaline phosphatase (P＜0.05). The level of serum urea nitrogen in 0.6% Met group was significantly higher than 0.2%, 0.4% and 0.5% Met groups (P＜0.05). The 0.5% Met group was the minimum of serum urea nitrogen, while alkaline phosphatase was significantly higher than the other groups (P＜0.05). Uric acid in 0.6% Met group was significantly higher than the other groups (P＜0.05), but no significant differences were found in albumin, total protein by different methionine levels (P＞0.05). According to quadratic curve estimation of the weight and feed/gain ratio, the optimal methionine levels were 0.466% and 0.507%, which could be averaged to 0.487%.【Conclusion】Combined with the average daily gain, feed/gain ratio, community evenness and other economic indicators, immune index, digestive system, index of blood, the optimal methionine requirement of Jinghong laying hens of 0-4 weeks is 0.49%.

Key words: feed , dietary methionine , Jinghong laying hens , growth development , organ development