Seasonal variations in the chemical composition and in vitro digestibility of some Spanish leguminous shrub species

The aim of this study was to determine the chemical composition and in vitro digestibility, and to estimate the in vitro fermentation parameters of leaves, stems, flowers and fruits of three browse legume species (Cytisus scoparius—Scotch broom, Genista florida—Iberian silver-leaved broom and Genista scorpius—scorpion’s thorn) harvested at different maturity stages from uplands in the province of León (Norwest Spain). Crude protein content varied from 123 g/kg dry matter (DM) observed in the mature leaves of G. scorpius to 290 g/kg DM of the young leaves of C. scoparius. The neutral detergent fibre and acid detergent lignin contents ranged from 220 to 662 g/kg DM and from 28 to 189 g/kg DM, respectively, the lowest values corresponding to young leaves of C. scoparius and the highest to the stems of G. florida harvested in summer. A large variability in in vitro digestibility and gas production kinetics was observed among and within species. With the exception of dry matter disappearance at 144 h of incubation and the asymptotic gas production, the highest digestibility coefficients and parameters of gas production kinetics corresponded to the flowers of each species and the lowest to their fruits and/or mature stems. Crude protein content, digestibility coefficients and parameters of gas production kinetics tended to decrease from spring to autumn, whereas cell wall contents followed the opposite trend. These seasonal variations were more pronounced in stems than in leaves. Based on the results presented herein, it is concluded that the leguminous species, specially their leaves and flowers, may represent a high quality feeding resource for grazing ruminants in the rangelands, particularly during dry seasons.