During force-feeding period, Mule ducks received increasing amounts of feed to force steatosis of the liver. The intensive lipogenesis is associated with high amount of energy to export as heat. The effects of ambient temperature on heat production and energy metabolism were tested on Mule ducks housed in an open-circuit respiration chamber. The metabolizable energy intake tended to be lower when ambient temperature was higher than 22 °C whereas total heat production was lower when ambient temperature was lower than 15 °C or higher than 22 °C, because ducks have reached their maximal ability of heat vaporization even at the lowest ambient temperature. Alternating periods of intense lipogenesis after the meal with periods of resting metabolism helps the ducks to adapt to high ambient temperature.