The article describes an influence of introducing to cow’s diet food supplements and propyleneglycol during the end of an interlactation period and after the calving on enzymatic activity of cow’s rumen contents. Complex supplement had positive impact on amylolytic activity in rumen, similarly to propyleneglycol (p<0,05), but also stimulating cellulolytic activity at the same time (p<0,01). Propyleneglycol has suppressed cellulolytic activity. Fat-splitting activity was not affected by neither adding propyleneglycol, nor by adding complex supplements. Change in these enzymatic activities had an impact on certain indicators of rumen fermentation. Thus, the concentration of volatile fatty acids (p<0,05) and of lactate (p<0,05) has increased, and the level of ammonia has decreased (p<0,05).