Hepatic glucose metabolism in dairy cows with or without grazing pastures in early lactation

The study objective was to evaluate the effect of grazing on early lactation changes in hepatic free glucose and glycogen concentrations and expression of genes related with gluconeogenesis in dairy cows. Primiparous Holstein cows (n=18, 3.2 +/- 0.2 BCS; fall calving) were used in a randomized block design and assigned, at calving, to two nutritional treatments during the first 61 days postpartum (DPP) of lactation: TMR ad libitum (TMR) or grazing of Medicago sativa plus 70% of TMR (PAS+TMR). Plasma and liver biopsies were collected at -7 and +42 DPP to measure plasma insulin and glucose, and hepatic free glucose and glycogen concentrations and mRNA abundance of genes related gluconeogenesis. Milk energy output was greater for TMR than PAS+TMR cows whereas plasma glucose and hepatic free glucose and glycogen concentrations did not differ between feeding strategies. Although insulin decreased from pre to postpartum, it was not affected by nutritional strategy. Hepatic pyruvate carboxylase (PC), citrate synthase (CS), and succinate dehydrogenase subunit D (SDHD) mRNA were greater while pyruvate dehydrogenase (PDH1A) mRNA tended to be less for TMR than PAS+TMR cows. Results would suggest TMR cows adapted their hepatic glucose and energy metabolism to the increased demands of their greater milk production.