Embryonic Thermal Programming combined with Fractionated Feeding induces Early Activation of Hepatic Lipid Storage Pathways in Mule Ducks

Recent studies have shown that fractionated feeding can promote the development of hyperphagic behavior in mule ducks. In parallel, embryonic thermal programming (TM) has been demonstrated to enhance hepatic energy storage under force-feeding conditions. In this exploratory study, we evaluated the combined effects of fractionated feeding and embryonic TM on short-term hepatic lipid accumulation in ducks. Two groups were compared: a CONTROL group (37.6°C during all incubation period) and a TM group (39.3°C for 16 hours per day from embryonic days 11 to 21). TM increased the embryonic relative expression of stress-response genes ( HSP90, HSP10, HSF5 ) compared to controls. At 7 weeks of age, the animals underwent a 5-day acclimation period during which they had access to feed for only 1 hour per day. After this acclimation phase, ducks were offered three voluntary 1-hour meals, spaced 12 hours apart, with a commercial growth diet. Liver weight, hepatic energy composition (glycogen and lipids), and expression of genes involved in hepatic metabolism were assessed before the first meal, 6 hours after each meal, and 24 hours after the last meal. Feed intake remained high during the first two meals but decreased during the third. Despite this, liver weight and energy content increased up to 6 hours after the third meal, peaking in total lipids and oleate proportion, accompanied by upregulation of lipogenic genes expressions ( ACC, ACLY, FASN, SCD1, ELOVL6 ) and downregulation of oxidative genes expressions ( ACOX1, CPT1a, ACSL1, ACAD11 ). Early activation of lipogenic gene expression in the TM group led to higher liver weight and lipid content after the first meal. However, this reflected a temporal shift in lipid synthesis rather than increased fattening, as no differences were observed at the end of the protocol. Overall, embryonic thermal programming modulates the timing of hepatic lipid metabolism in ducks under voluntary fractionated feeding. This exploratory approach requires further optimization, particularly to prolong the transient hyperphagia observed. Nevertheless, it provides a first step toward understanding how nutritional strategies combined with embryonic programming may influence hepatic lipid deposition.