Docosahexaenoic acid (DHA) alleviates hepatic lipid deposition in dairy cows during the transition period: an integrated in vitro and in vivo study

Abstract Background Fatty liver syndrome is a prevalent metabolic disorder in transition dairy cows, characterized by excessive hepatic lipid accumulation that impairs liver function and leads to systemic metabolic disturbances. Docosahexaenoic acid (DHA), a prominent n-3 polyunsaturated fatty acid (PUFA), not only exhibits anti-inflammatory and anti-oxidative properties, but also holds potential in ameliorating lipid metabolism. This study integrated in vitro bovine primary hepatocyte models and in vivo dairy cow trials to investigate the regulatory effects of DHA on hepatic lipid deposition. Results In vitro, 40 μmol/L DHA significantly reduced triglyceride (TAG) accumulation in steatotic hepatocytes by downregulating genes involved in fatty acid transport (FABP-1, CD36) and lipogenesis (DGAT2, FAS, SREBP-1C), while upregulating markers of lipolysis (CGI-58, ATGL) and fatty acid oxidation (ACADL, CPT1A, CPT2). Transmission electron microscopy (TEM) confirmed DHA-mediated restoration of mitochondrial ultrastructure and enhanced lipid droplet (LD)-mitochondria interactions. In vivo, dietary rumen-protected DHA (180 g/d) supplementation reduced hepatic lipid deposition, improved liver function (evidenced by decreased total bilirubin and alanine aminotransferase), reduced oxidative stress and inflammation (suppressed malondialdehyde, glutathione peroxidase, and lipopolysaccharide), coincided with relieving insulin resistance (reduced insulin and glucose, as well increased adiponectin) in dairy cows with fatty liver. These improvements may be attributed to increased expression of TOMM20 and MtCo-1, promoting mitochondrial biogenesis and β-oxidation, along with an elevated plasma n-3/n-6 ratio. Conclusions Collectively, these findings suggest that DHA supplementation represents a promising nutritional strategy for preventing spontaneous fatty liver in transition dairy cows by enhancing hepatic lipid clearance and restoring metabolic homeostasis.