Two experiments were performed to investigate the effect of zinc sulfate (ZnS), zinc oxide (ZnO) and zinc methionine (ZnM) on degradability of alfalfa hay and wheat straw. To the syringes one of the following treatments were applied:1) no added zinc (C) ,2) 500 ppm of Zn as ZnS; 3) 500 ppm of Zn as ZnO; 4)500 ppm of Zn as ZnM. The results indicated there were not significant differences between treatments in term of gas production measurements for wheat straw. In case of alfalfa hay, supplementation of rumen fluid with ZnM significantly (P<0.05) increased gas production after 48 h of incubation. At this stage ZnO had a little effect on gas production. Addition of ZnM led to a faster response of microbial fermentation compared to other Zn sources. However, supplementation with the rumen fluid zinc supplements had no effect on gas production during fermentation of wheat straw probably due to low nitrogen content of wheat straw which can not stimulate a normal microbial growth. Therefore, further works are required with other feedstuffs to identify the interaction between Zn sources and feed characteristics.

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