ABSTRACT The study evaluated the effect of heat-treating apple (Malus domestica Borkh.) pomace with different oven temperatures on chemical composition and in vitro ruminal fermentation with or without polyethylene glycol (PEG). Eight replicate samples of air-dried fresh apple pomace (CON) were each oven-dried for 30 min at 60°C (T60), 80°C (T80), 100°C (T100), 120°C (T120), and 130°C (T130). Heat treatment increased (P < 0.05) dry matter, organic matter, neutral detergent fibre and acid detergent fibre of the pomace. The untreated pomace (CON) had the highest crude protein content (94.0 g/kg DM) while the lowest was from T180 (49.84 g/kg DM). The inoculation with PEG had higher cumulative gas production than the one without PEG. Similarly, PEG inoculation increased (P < 0.05) the rate of gas production from fraction b (c), effective gas production, and partitioning factors. It was concluded that heat treatment does not improve the nutritive value of apple pomace.