Fermentation Kinetics and Digestibility of Cultivated Mediterranean Leguminous Shrubs: Effects of Season, Plant Part and Irrigation

This study evaluates the effects of plant part (leaves vs. stems), harvest season (spring vs. autumn), and irrigation on the chemical composition, in vitro ruminal fermentation kinetics, and digestibility of three Mediterranean leguminous shrubs: Acacia fimbriata, Medicago arborea and Anthyllis barba-jovis. Samples were collected under field conditions, analysed for chemical composition, and assessed for in vitro ruminal fermentation, including incubations with and without polyethylene glycol (PEG) to assess the biological activity of phenolic compounds. Crude protein and fibre fractions did not differ significantly among species; ash was highest (p < 0.05) in Ac. fimbriata. In vitro fermentation kinetics were similar among species; however, the response to PEG was higher (p < 0.05) for Ac. fimbriata than for M. arborea and An. barba-jovis. In vitro digestibility was superior (p < 0.05) in M. arborea and An. barba-jovis. Leaves contained higher ash and protein contents and less fibre than stems, resulting in greater gas production, fermentation rate, and digestibility (p < 0.05). Spring-harvested fodder showed higher digestibility than autumn samples. Irrigation had negligible effects, except for a marginal numerical but nonsignificant (p = 0.05) greater extent of degradation observed in browse prior to irrigation. Overall, M. arborea showed a better nutritional quality, whereas Ac. fimbriata was the species with the lowest nutritive value. Forage quality was strongly influenced by plant part and harvest season, with leaves and fodder in spring showing superior potential as a feedstuff for ruminants.