Undersowing is a method of supplementing and enriching species composition of grasslands without interfering in soil habitat. The method brings about an increase of grassland biodiversity and allows for maintaining many local ecotypes of fodder grasses in meadow sward. The aim of the study was to assess the effect of enrichment of meadow sward through direct undersowing short-term intensive grass varieties of high fodder value on the quality of produced fodder. The experiment was set up on a meadow of simplified floristic composition on alluvial soil in drying riparian habitat in Żuławy Elbląskie. Two weeks before undersowing the meadow was sprayed with herbicide Fernando 225 EC at a dose of 3 l·ha-1. Undersowing was made in the end of September 2012. Assessment of fodder quality from sward undersown with special mixtures was performed in the years 2013-2015 according to RFV index. Obtained results showed that tetraploid varieties Lolium perenne, Lolium×boucheanum and Festulolium braunii, which constituted 5 - 25% of the sward, and the frequency of mowing were the main factors affecting fodder quality. The use of Lolium×boucheanum and Festulolium braunii significantly improved the quality of produced fodder and thus increased the potential milk production from 1 ha of undersown meadow.