Seasonal changes of diet composition of sheep grazing on Leymus chinensis grassland

Nalkane technique is considered to be the most accurate method to estimate diet composition of sheep, and the additionally introduced markers (longchain alcohols and longchain acids) further extended the range of available faecal markers, making it possible to estimate the diet with complex components. In this experiment, the dietary composition of sheep grazing on Leymus chinensis grassland was estimated using alkanes in combination with alcohols and/or acids during the grazing months. The results showed that L.chinensis, Carexdur iuscula and Suaeda heteroptera were the main diet components during the whole grazing seasons, but with evident seasonal changes. In June, the bulk of the diet was made up of S.heteroptera and L.chinensis, C.iuscula came after. In July, the consumption of S.heteroptera and C.iuscula faced a significant decline, but of L.chinensis increased obviously. In August, C.iuscula constituted the most proportion, and the consumption of L.chinensis and S.heteroptera decreased and increased, respectively. For the minor components, like Atriplex patens, Toraxacum mongolicum and Phragmites communis, nonsignificant changes were observed. The plant species distributed vertically and horizontally influenced on the grazing behavior of sheep heavily. In addition, palatability was another influencing factor. The analysis of selectivity index showed that the plant species, like L. chinensis, with high proportion in the diet presented low selectivity. Similarly the low proportion components, like P.communis and A.patens，might show high selectivity.