Résumé
The effect of extended gradually obligatory underfeeding on milk yield, some milk and blood contents was studied in lactating Friesian cows. The animals were firstly fed on basal lactating diet. The diet was then gradually and weekly restricted for a period of 8 weeks. Blood serum contents showed restriction and thereafter. There was a significant decrease of total serum protein, glucose, calcium and inorganic phosphorus in the second week. Serum magnesium began to decrease in the third week. A significant elevation of total serum lipid recorded in the first week and thereafter. It could be concluded that a physiological response [of milk yield and its fat%] and biochemical alterations [of blood serum contents] indicated the change in metabolism when feed supply was gradually restricted in lactating cows fed on low levels of nutrition