This experiment was conducted to estimate the diet composition of grazing sheep by nalkane technique. In 4. 4 hm2 grazing plots, eight Mongolia sheep were grazing, and their diet composition was estimated by n-alkanes as markers on June, September and December, respectively. The results showed that there was a difference in concentration of n-alkanes among 4 species forages, which C27and C31 were most significant, C33 took the second place, and C29 was the poorest. The diet composition of sheep had significant change with grazing seasons. In summer,the mainly diet of sheep was Artemisia frigida , Cleistogens songorica and Convolvulus ammannii, account for 79. 68％,12. 12％ and 7. 30％ respectively, while Stipa breviflora only 0. 90％.In autumn, the sheep started to consume Stipa breviflora with the pasture of good palatability reduced, increased from 0. 90％ to 3. 81％, and Cleistogens songorica intake increased from 12. 12％to 23. 57％. In winter, the pasture species reduced of sheep consumed, Artemisia frigida occupy 86. 26％ of the total pasture intake, CLeistogens songorica and Convolvulus ammannii reduced to 8. 33％ and 5. 41％ ,respectively, while Stipa brevifLora didn't consumed. In conclusion, n-alkane technique can provide an accurate estimation of diet composition of grazing sheep.%为进一步研究饱和烷烃技术在放牧绵羊食性测定中的应用,本研究在4.4 hm2放牧试验区内,放牧8只蒙古羊,分别于6、9和11月利用饱和烷烃技术对放牧绵羊的食性进行测定.结果表明,同一季节,不同牧草的烷烃模式存在差异,其中以C27和C31差异最为显著,C33次之,C29最差.绵羊的食性表现出明显的季节性变化,夏季羊只所食的牧草主要以冷蒿、无芒隐子草和银灰旋花为主,分别占79.68%、12.12%和7.30%,而短花针茅只占0.90%;而进入秋季后,随着适口性好植物密度的降低,羊只开始对短花针茅进行采食,由原来占食入牧草总量的0.90%升高到3.81%,同时无芒隐子草的采食量也开始增加,由原来占食人牧草总量的12.12%提高到23.57%;冬季家畜采食牧草的种类开始减少,冷蒿占羊只采食量的86.26%,无芒隐子草和银灰旋花分别减少到8.33%和5.41%,而对短花针茅不采食.综上,饱和烷烃技术可以准确测定短花针茅荒漠草原放牧绵羊的食物组成.
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