A field study on characteristics and diversity of gene expression in the liver of dairy cows during the transition period.

Metabolic and endocrine adaptations to support milk production during the transition period vary between individual cows. This variation between cows to adapt to lactation may have a genetic basis. The present field study was carried out to determine hepatic adaptations occurring from late pregnancy through early lactation by measuring mRNA abundance of candidate genes in dairy cows on-farm. Additionally, the objective was to observe the diversity in inter-individual variation for the candidate genes that may give indications where individual adaptations at a molecular level can be found. This study was carried out on-farm including 232 dairy cows (parity >3) from 64 farms in Switzerland. Blood and liver samples were collected on d 20±7 before parturition, on d 24±2, and on d 89±4 after parturition. Blood plasma was assayed for concentrations of glucose, nonesterified fatty acids, β-hydroxybutyrate, cholesterol, triglycerides, urea, albumin, protein, insulin, insulin-like growth factor-1, leptin, 3,5,3'-triiodothyronine, and thyroxine. Liver samples were obtained at the same time points and were measured for mRNA abundance of 26 candidate genes encoding enzymes and nuclear receptors involved in gluconeogenesis, fatty acid β-oxidation, fatty acid and triglyceride synthesis, ketogenesis, citric acid cycle, cholesterol synthesis, and the urea cycle. The cows in the present study experienced a marked metabolic load in early lactation, as presented by changes in plasma metabolites and hormones, and responded accordingly with upregulation and downregulation of almost all candidate genes involved in metabolic processes in the liver. The observed inter-individual variation for the candidate genes, which was highest for acetyl-CoA-carboxylase and glycerol-3-phosphate dehydrogenase 2, should be further investigated to unravel the regulation at molecular level for optimal adaptive performance in dairy cows.