Influence de la mise à jeun sur l'aminoacidémie libre, l'urémie et la glycémie chez la vache laitière

Abstract

protein mobilization, glycemia and milk yield dropped (P < 0.05) on the 2nd day of fasting. The fall in plasma glucose probably resulted from a continuous glucose uptake by the mammary gland for milk lactose synthesis which was not entirely compensated by gluconeogenesis. Within-day variations in plasma metabolites were observed, but these variations were generally lower during fasting than during feeding, especially for plasma glucose which showed variation with time of day during both fasting days. It was concluded that, as in dry cows, a 2-day fasting enhances muscle proteolysis in lactating cows. Contrary to dry cows, however, gluconeogenesis mechanism which attempts to maintain glucose homeostasis becomes insufficient in lactating cows to avoid a drop in glycemia from the 2nd day of fasting. The decrease in milk yield might be, at least partly, the result of that drop in glycemia. Finally, the time course from the last meal is a factor affecting within-day variations of plasma metabolites.