Abstract: This study aimed to investigate the optimal proportion of millet stalks in a mixed diet of millet stalks and alfalfa hay. Five small-tailed Han sheep with permanent rumen fistulae were selected as experimental animals and a 5×5 Latin square design was set up with five individual sheep as replicates to test each of five dietary mixtures. All five diets were composed of a 40∶60 mixture of concentrate and roughage. However, the roughage varied in the proportion of millet stalks and alfalfa hay (0∶100, 100∶0, 25∶75, 50∶50, 75∶25, for diets Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ, respectively). The digestibility and effective degradability (ED) of major nutrition composition in diets were measured using Nylon-bag technique. ED_DM and ED_CP were used as the primary assessment index to calculate an associate effects index (AEI); ED_NDF and ED_ADF were used as a secondary index to reveal the mechanism of the associative effect between millet stalks and alfalfa hay. It was found that: 1) The ED of DM, CP, NDF and ADF was significantly increased with increasing proportion of alfalfa hay (P<0.05). 2) The AEI of groups Ⅲ, Ⅳ, and Ⅴ was 0.8%, 4.0% and 3.7%, respectively, when the ED_DM was the only evaluation index, while the AEI of groups Ⅲ, Ⅳ, and Ⅴ, was 2.5%, 3.5% and 3.1%, respectively, when the ED_CP was the only evaluation index. Thus, diet Ⅳ was the best. 3) In diets Ⅲ, Ⅳ, and Ⅴ the respective contributions of CF to the AEI_DM were 101.55%, 68.75% and 55.41%.

Key words: alfalfa hay, millet stalks, Nylon-bag technique, effective degradability, associate effects