The aim of the study was to determine the nutrient composition and in vitro digestion parameters of Jerusalem artichoke (Helianthus tuberosus L.) herbage at different maturity stages (vegetative, early flowering, full flowering and early seeding) in horses and ruminants. The crude protein (CP), ether extract (EE), ash, non-fibrous carbohydrate (NFC), neutral detergent fibre assayed with a heat stable amylase and expressed exclusive of residual ash (aNDFom), acid detergent fibre expressed exclusive of residual ash (ADFom), acid detergent lignin (ADL), total condensed tannins (TCT), total saponin (TSP) and carotenoids (lutein, zeaxanthin, lycopene and alpha-,beta-,gamma-carotenes)content in plant samples were analysed. The in vitro total gas and methane production, metabolizable energy (ME), true dry matter disappearance (T-DMd), true organic matter disappearance (T-OMd), gas yield (GY24), partial factor (PF24) and microbial crude protein production (MCP) values and volatile fatty acids (VFAs) concentration in fermentation fluid for herbage samples were determined with the in vitro digestion techniques carried out using horse faeces and ruminant fluids. The aNDFom, ADFom, ADL, EE and TCT content increased with plant maturation (P < 0.05). Zeaxanthin, lycopene and beta-carotene content was the highest in full flowering and the lowest in early seeding plant (P < 0.05). With the plant maturation the following parameters decreased (P < 0.05): CP, NFC, ash and TSP content in plant samples, and in vitro total gas and methane production, T-DMd, T-OMd, ME values and molarities of individual VFAs for both horses and ruminants. Consequently, Jerusalem artichoke herbage, especially at vegetative stage, has the potential to be used as quality forage in terms of high/moderate nutrient composition and satisfactory digestion values for both horses and ruminants.