EFFECTS OF CULTIVAR AND HARVEST DATE ON THE COMPOSITION OF NITROGEN FRACTIONS IN FESTULOLIUM HERBAGE

Grasses of ryegrass (Lolium) and fescue (Festuca) genera play an important role in the nutrition of high-yielding dairy cows, but fescue x ryegrass hybrids (Festulolium braunii) are also increasingly used. The growing popularity of F. braunii can be attributed to its supreme agronomic traits, combining the high yield potential of ryegrass: Lolium multiflorum and Lolium perenne, and the high resistance of fescue: Festuca pratensis, F. arundinacea and F. arundinacea var. glaucescens, to biotic and abiotic factors. The aim of this study was to analyze the composition of nitrogen fractions in the herbage of different Festulolium braunii cultivars harvested at different dates. Three F. braunii cultivars were studied: Felopa, Lofa and Perun. The chemical composition of herbage (dry matter - DM, crude protein - CP. water-soluble carbohydrates - WSC, neutral detergent fiber - NDF, acid detergent fiber - ADF) and nitrogen fractions (A, B-1, B-2, B-3, C) were determined in accordance with the Cornell Net Carbohydrate and Protein System (CNCPS). in the analyzed forages, highly significant differences (P < 0.01) were noted in the content of DM and WSC, which were affected by both experimental factors. Significant (P < 0.05) differences in the NDF content of herbage were found between cultivars. In the analyzed forages, significant differences (P < 0.05) were noted in CP, which was affected by both experimental factors. The cultivar Felopa had the highest CP content. The content of WSC decreased at successive harvests. The cultivar Lofa had the highest crude fiber content and a lower content of WSC than the remaining Festulolium hybrids. The harvest date had a significant effect on the composition of all nitrogen fractions, and the proportions of fractions B-2, B-3 and C were also highly significantly (P < 0.01) affected by a cultivar. The composition of fractions B-3 and C was influenced by both experimental factors at P < 0.01. Significant (P < 0.05) differences were observed for fractions A. In all analyzed forages, fraction B-2 had the highest share of the total nitrogen pool. The share of fraction B-3 increased, whereas the content of fractions B-1 and B-2 decreased in fourth-cut herbage. The share of acid detergent-insoluble nitrogen (ADIN) increased at successive harvests, which decreased the nutritional value of forage.