Principal component analysis showing the grouping and separation of the by-products based on chemical composition, in vitro digestibility and fermentation kinetics: OLV (olive tree leaves), PPS (pepper skins), GPS (grape seeds), ARTd (hay of artichoke by-products), GBH (green bean haulms), ASP1 (asparagus rinds 1), BRH (broccoli stalk hay), ARTs (ensiled artichoke by-products), TMP (dried tomato pulp), APP (apple and pear pomace), APL (apple pomace), LTC (lettuce leaves), PPC (pepper cores), ALH (almond hulls), GBB (green bean haulms and sugar beet pulp), SBR (sugar beet rootlets, hairs, root tips and beet tails), PHL (pea haulms), BBH (broad bean haulms), ASP2 (asparagus rinds 2), SBT (sugar beet tops and leaves), CPC (clementine pulp), CPO2 (orange pulp 2), CPL (lemon pulp), CPO1 (orange pulp 1), SBPd (sugar beet pulp dehydrated) and SBPs (ensiled sugar beet pulp).