Effect of season on chemical composition and in vitro digestibility of six native forage shrubs species grazed by goats in protected areas in canary islands, Spain

Chemical composition (organic matter, crude protein and fiber fractions), in vitro organic matter (OM) digestibility and metabolizable energy (ME) of six native shrubs regularly browsed by goats in a natural protected area in Canary Island has been determined in two seasons (dry and wet) along the year. Means values for each individual species, for wet and dry seasons and for species by season were compared. Chemical composition and in vitro digestibility mean values vary significantly among the six species (Chamaecytisus proliferus subsp. meridionalis, Teline microphylla, Adenocarpus foliolosus, Echium onosmifolium, Echium decaisnei and Dittrichia viscosa). In general, they have a medium to high crude protein (CP) and high fiber contents. A. foliolosus (181 g/kg DM) and Ch. proliferus (162 g/kg DM) were the species with highest CP contents. Comparing both seasons' means for the whole of the species, OM, CP and lignin contents showed no significant differences between dry and wet seasons while the rest of fiber fraction and DM values were significantly lower in the wet season. Analyzing the effect of season inside species, differences between dry and wet seasons were no significant for most variables; i.e., in general there was not great variability of analyzed component throughout the year for each individual species. The estimated ME content ranged between 8.4 MJ ME/kg DM for T. microphilla (dry season) and 12.1 MJ ME/kg DM for Ch. proliferus (wet season). Grazing utilization by goats of these browses in the local conditions guarantees a regular intake of analyzed components along the year