Simple SummaryMore than 10 million tons of coffee are consumed annually in the world, generating two kg of wet spent coffee grounds per kg of coffee consumed, which are considered food waste. Despite the interesting nutritional value of spent coffee grounds for ruminant feeds, their fibre fraction is very high, which presents a limitation for including this alternative ingredient in animals’ diets due to its low digestibility. This study considered thermal and mechanical treatments combined with enzymatic hydrolysis to improve the spent coffee grounds’ nutritive value and digestibility. The main conclusions are that the effect of enzymatic treatments is overwhelmed by the action of ruminal bacteria and that diminution of the particle size is the best strategy to improve the spent coffee grounds’ digestibility.AbstractLignin in animal diets is a limiting factor due to its low digestibility. This study assessed the effects of thermal or mechanical pre-treatments and enzymatic hydrolysis on spent coffee grounds’ (SCG) nutritional value and digestibility. A first trial studied the effect of thermal pre-treatment and hydrolysis with removal of the liquid part and a second trial studied mechanical pre-treatment and hydrolysis with and without removal of the liquid part. Autoclaving did not improve the enzymatic performance nor the nutritional value. Hydrolysis reduced the digestibility of the solid phase and impaired its ruminal fermentation efficiency. Hydrolysates without removing the liquid part improved its nutritional value, but not compared with unprocessed SCG. Grinding increased crude protein and reduced crude fibre and protein, which led to greater fermentation and in vitro digestibility. Thus, grinding emerges as the most promising valorisation strategy to improve SCG nutritional characteristics and their use for animal feed, contributing to the circular economy.