This study was designed to compare the evolution in nutritive value between two permanent grasslands that had different botanical composition, during 2 years (2003 and 2004), and to study the relationships between a set of vegetation and digestibility characteristics. Botanical composition, lamina proportions (LP), and in vivo organic matter digestibility (OMD) of grasslands were measured at three different times during the first growth cycle over 2 years: last week in May, third week in June and second week of July. Foliar traits [specific leaf area (SLA) and leaf dry matter content (LDMC)] were measured on grasses in the first period of both years. The LDMC and botanical composition values were used to calculate plant functional types (PFT) of the grasslands at each period. Relationships between OMD and SLA, LDMC, LP and forbs proportions (FP) were tested. Grassland rich in forbs, which was classified in PFT B, showed higher OMD in the first stage of maturity and lower OMD at the end of the cycle in 2004 than grassland rich in grasses, which was classified as PFT C. There were significant relationships between LDMC and OMD across the two first periods. There were also significant relationships between LP and OMD in the first period and between FP and OMD in the third period. The botanical composition of the grassland and consequently its PFT is an important factor explaining the evolution of the nutritive value of permanent grasslands during the first growth cycle.