The aim of the experiment was to determine the effects of the foliar application of Tytanit, at the same time comparing it with the effects of mineral nitrogen, on the cellulose and hemicellulose content and its effect on Festulolium braunii digestibility. The experiment was founded in the spring of 2014 in the field of the University of Natural Sciences and Humanities in Siedlce, Poland. The plant used in the experiment was the Felopa variety of Festulolium braunii. The effects of Tytanit foliar application at a concentration of 0.2% and 1% and of mineral nitrogen at a dose of 80 and 160 kg/ha were studied in the experiment. During its full use (2015–2017), Festulolium braunii was harvested three times. The content of cellulose and hemicellulose was determined by near-infrared reflection spectroscopy (NIRS) using the NIRFlex N-500. The higher dose of 1% Tytanit contributed to an increase in cellulose content of Festulolium braunii (334.8 g kg−1), at the same time decreasing hemicellulose content (175.0 g kg−1), lignification degree (7.1%), dry matter digestibility (59.71%), and total digestible nutrient content (52.99%).