Adaptive responses to fractionated feeding: transient hyperphagia and reversible hepatic lipid deposition in mule ducks.

This study examines a fractionated feeding protocol and analyzes its effects on feed intake and hepatic energy storage in mule ducks. The protocol was applied to 140 animals and included a 5-day acclimation phase with time-restricted feeding (1 h without quantitative restriction), followed by 21 one-hour meals delivered every 12 h, characterized as the fattening phase. Animals were then returned to ad libitum continuous access to food (24 h/day). During the acclimation phase, feed intake increased from 154.97 ± 23.31 to 316.04 ± 22.72 g/animal/meal, reaching 584.59 ± 47.16 g per animal on the first day of fattening phase. Intake remained higher than under ad libitum feeding during the first four days of the fattening phase before stabilizing at around 300 g/day/animal. Different measure and sampling were performed before the first meal of the fattening phase, 6 h after the third meal, and after each odd-numbered meal up to the 21st, as well as after the 4-day return to ad libitum feeding. Mean liver weight was 66.6 ± 10.6 g before the first meal, increased to 134.0 ± 25.2 g after the third meal, and then decreased thereafter to reach 97.4 ± 18.6 g after the 21th meal. However, liver weight remained higher than under fasting and ad libitum feeding conditions for most of the fattening period. Hepatic glycogen remained high (10-15 %) between the third and 21st meals, corresponding to the maximum level achievable by the liver and higher than under continuous ad libitum feeding. Total hepatic lipids increased from 5.54 ± 0.542% before the first meal to 7.68 ± 1.55% after the third meal, before decreasing from the fifth meal onward and gradually returning to their initial level over the entire fattening period. Transcript levels were higher after the third meal than those measured prior to the first meal and under ad libitum feeding conditions for ACC, FASN and ELOVL6. Subsequently, expression levels declined to intermediate values, paralleling the decrease in total lipid content. Overall, although lipid accumulation remained limited, the protocol maintained near-maximal hepatic glycogen levels, a key prerequisite for fattening.