Abstract
Dairy cows experiencing negative energy balance (NEB) are prone to metabolic and inflammatory disorders, including ketosis, fatty liver, mastitis, endometritis, and hypocalcemia, which impair productive and reproductive performance. NEB elevates non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHBA), leading to disrupted lipid metabolism characterized by increased fatty acid synthesis (via SREBP-1c, ACC, FASN), impaired lipid export (downregulated MTTP, ApoB100, ACAT2), and reduced oxidation (suppressed SIRT1-PPARα-CPT1A/2 pathway), resulting in triacylglycerol (TAG) accumulation and ketosis. Excess reactive oxygen species (ROS) trigger oxidative and endoplasmic reticulum (ER) stress and apoptosis through JNK, p53/Nrf2, and PERK-eIF2α signaling, while HIF-2α-mediated hypoxia aggravates hepatic damage. Elevated NEFA/BHBA impair polymorphonuclear neutrophil (PMN) chemotaxis and phagocytosis, promoting mastitis and endometritis, and hypocalcemia further weakens immune defense. Rumen-protected choline (RPC) improves lipid metabolism by enhancing VLDL assembly and TAG export (upregulating MTTP, ApoB100, ATG3; inhibiting SREBF1, DGAT2), stimulating fatty acid oxidation (activating AMPK-PPARα-CPT1α), and reducing oxidative stress (suppressing ROS-ERN1). Moreover, RPC decreases IL-6 and TNF-α levels and enhances antioxidant capacity and PMN function. Overall, RPC alleviates NEB-induced metabolic and inflammatory diseases, supporting its inclusion in periparturient management to mitigate NEB and associated disorders.