Abstract: 20 Kazakh lambs had an average weight of (24.71±2.07) kg,which were selected randomly as subject investigated with 4 months of age from Yili Natural Grassland in the North Bank of Turks River. The research surveyed and evaluated the changes of weight, feed intake, serum biochemical indicators and hormone contents from 2008 May 15 to September 23. The results indicated that the average daily weight gain of lambs from 4 to 8 months of age were 175 g±34 g, 92 g±36 g, 158 g ±46 g and 81 g±36 g, respectively. It reached two peaks that were 4 to 5 and 6 to 7 months of age and it were higher than other months of age. From 4 to 8 months of age, respective dry matter intake of 0.65 kg±0.21 kg,1.45 kg±0.32 kg,1.74 kg±0.48 kg, 1.95 kg±0.50 kg and 2.30 kg±0.45 kg significantly increased (P<0.01).Hormone contents determination indicated that the highest NPY contents in the whole period appeared in 5 months of age (39.10 pg/mL±2.60 pg/mL), then the lowest NPY contents in 7 months of age (36.87 pg/mL±1.10 pg/mL). No difference was found in CCK, PP, SS and CORT contents in different ages of grazing lambs, however, the highest contents of CCK, PP, SS and CORT appeared in 4 months of age (45.19 pg/mL±9.70 pg/mL), 8 months of age (108.53 pg/mL±19 pg/mL), 6 months of age (160.34 pg/mL±10 pg/mL) and 4 months of age (22.1 ng/mL±4 ng/mL), respectively. GAS and T contents increased linearly by age, the highest T4 contents appeared in 5 months of age (78.3 ng/mL±12.7 ng/mL) while the lowest appeared in 7 months of age (65.83 ng/mL±13 ng/mL). Regularity for changes of MTL, SEC, GH, INS and T3 were the same, increased in 4 to 5 and 6 to 7 months of age, but decreased in 5 to 6 and 7 to 8 months of age.

Key words: grazing lambs; growth and development; hormone