This work addresses the dynamic of phenological development on mean stage weight (MSW), chemical composition, (ash, nitrogen (N), neutral detergent fibre (NDF) and acid detergent fibre (ADF) contents, and pepsin-cellulase dry matter digestibility (PCDMD) for cultivars of six perennial grass species (timothy, ryegrass, cocksfoot, sheep’s fescue, red fescue and meadow foxtail), during their first growth cycle. The study was performed over two years along 3 sites distributed along an altitudinal gradient. The dynamics of MSW, N, NDF, ADF and PCDMD for the species differed according to the environment. For a given sum of temperatures, at Clermont-Ferrand (CL; 350 m), MSW was delayed (note of 2.37) compared with Saint-Genès-Champanelle (SG; 850 m; note of 2.97) and Laqueuille (LA; 1100 m; note of 3.02). Consequently, the NDF and ADF contents were lower and the PCDMD value was higher in the cultivars established at CL (575 g/kg dry matter (DM), 287 g/kg DM and 0.64 respectively) than in those at SG (653 g/kg DM, 349 g/kg DM and 0.51 respectively) and LA (653 g/kg DM, 343 g/kg DM and 0.52 respectively). In all sites, and for the two years, the PCDMD content of timothy (0.60), ryegrass (0.63) and cocksfoot (0.59) cultivars were higher than that of sheep’s fescue (0.47), red fescue (0.53), and meadow foxtail (0.51). The only exception was identified for CL site in the first year of the study, when the dynamic of PCDMD was similar for all cultivars. Sum of temperatures and MSW were closely related to nutritive value of forage, but neither indicator fully described the nutritive value of perennial grasses.