Abstract: 55 Kazak male lambs chosed, body weight and body size were carried out at the north bank of Tekas natural grassland, Zhaosu horse farm, Yili Kazak Autonomous Prefecture in Xinjiang from May 15 to September 28, 2008. 20 lambs were selected for digestion. The results showed that the entire research period, there was a fluctuation in the growth of lambs pastured as the seasonal variations in forage. The growth of lambs reached the highest level at 5 months and 7 months, respectively. The body weight gain overally increased. There was significant difference in the average body weight gain of the lamb aging 7 or 8 months (P<0.05). However, there was obvious significant difference in average body weight gain of the remaining lamb (P<0.01). The monthly average daily gain were (187.8±55.7) g,(100.1±44.7) g,(174.6±45.2) g and (82.1±36.0) g, respectively.Growth rate of pastured lamb body size of 5 months old lamb was bigger than that of 6 months old one, 7 months old lamb was bigger than that of 8 months old. In addition to thoracic deep, the order of the cumulative growth rate of the pastured lamb body size from big to small were chest, body length, body height, thoracic deep, wide chest, tube circuit, respectively. The DM, OM, CP digestion rate of 5 months old lamb were significantly higher than that of 4 months old one(P<0.01). There was decrease in DM digestion rate between 5 and 7 months, the difference between 5 and 7 months was significant (P<0.01). There was consistent in OM digestion rate between 6 and 7 months, there was biggest when 8 months. There was decrease in CP digestion rate between 5 and 8 months, there was no significantly difference between 7 and 8 months, However, there was significant difference in the CP digestion rate for the rest of the months (P<0.01).

Key words: body weight; feed digest; intake; grazing lambs