[Non-genetic factors influencing on milk and butterfat production of European Holstein-Friesian cows in a seasonal calving system at the 10 region. 1: Effects of year and month of calving]

allaitement bovin laitier breeds condiciones ambientales condition de milieu cows dairy cattle environmental conditions ganado de leche grasa de la leche lactancia lait leche milk milk fat parto parturition primavera printemps race razas spring suckling vaca vache