INTRODUCTION: This study aimed to evaluate, using the METHODS: The by-products were included at 10% dry matter in the control (CTR) diet, commonly adopted for adult sheep (80% natural grassland and 20% concentrate), and incubated at 39°C under anaerobic conditions. RESULT AND DISCUSSION: After 24 h of the incubation, the organic matter degradability (OMD24h) and methane production were assessed. After 120 h of the incubation, the organic matter degradability (OMD120h), volume of gas produced (OMCV), fermentation kinetics, pH, volatile fatty acids (VFAs), and ammonia were evaluated. Dunnett's test was used to compare the differences between the control and experimental diets, and multivariate analysis was performed to highlight the differences among the diets based on their