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

Abstract

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 Aprilwere 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.