Liver apolipoprotein B₁₀₀ expression and secretion are down-regulated early postpartum in dairy cows

Fatty liver is a typical condition early postpartum in dairy cows. The aim of the present study was to evaluate gene expression, synthesis and secretion of liver apolipoprotein B₁₀₀ (Apo-B₁₀₀) in periparturient dairy cows. The relationships between Apo-B₁₀₀ with liver lipid accumulation, and metabolic and oxidative status were also investigated. The trial was carried out in a commercial dairy herd. Sixteen multiparous Holstein cows due to calve in April were monitored from 30 d prepartum to 35 d postpartum. Milk yield was recorded, and body condition (BCS) of cows was scored. Blood samples were taken at − 30±3, − 18±2, and − 4±1 d prepartum (before expected calving) and at 3, 17, and 35 d postpartum. Plasma and erythrocyte samples were obtained and analyzed. Glucose, NEFA, BHBA, cholesterol, albumin, Apo-B₁₀₀, reactive oxygen metabolites, thiol groups, and glutathione peroxidase were determined in plasma. Reactive oxygen metabolites, thiol groups, glutathione peroxidase and superoxide dismutase were determined in erythrocytes. Liver biopsies were performed on d − 30, 3, and 35 relative to day of calving. Liver samples were analyzed to determine fat accumulation, Apo-B₁₀₀ mRNA and Apo-B₁₀₀ protein. Milk yield, BCS, and plasma indices of metabolic status showed expected changes for that physiological phase. Oxidative status indices indicated an oxidative stress condition early postpartum. Fat accumulation in liver increased after calving and no significant difference was found between values observed at 3 and 35 DIM. Gene expression as well as cellular and plasma concentration of Apo-B₁₀₀ were higher prepartum compared with postpartum. Apo-B₁₀₀ mRNA was not different between 3 and 35 DIM, whereas both cellular and plasma Apo-B₁₀₀ increased from 3 to 35 DIM. The study demonstrates that Apo-B₁₀₀ is regulated at the level of transcription and post-transcription. Changes of gene and protein Apo-B₁₀₀ expression may contribute to the accumulation of triglyceride in liver taking place early postpartum in dairy cows.