FGF21 and obesity due to melanocortin 4 receptor deficiency: Given that MAPK1 has been identified as a crucial mediator through which FGF21 modulates lipid homeostasis and energy balance, and considering that FGF21 is a promising therapeutic target for addressing lipid metabolic dysfunction in obesity [21], our subsequent experiments specifically aimed to investigate whether FGF21 is involved in the MAPK1-mediated regulatory role in lipid metabolic disorders in the context of bovine ketosis.