ChileanJAR

The effect of three phenological stages and two post-grazing residues of alfalfa (Medicago sativa L.) were evaluated on milk production by lactating dairy cattle. The growth stages evaluated were: pre-bud, 10% flower and 50% flower. Post-grazing residues were high and low. All factors where evaluated in a completely randomized block design with a 3 x 2 factorial arrangement. The trial was conducted in two periods: between November and January (period I) and January and March (period II). Ninety-six Holstein-Friesian cows were used, 48 in each period. In both periods milk production was affected by the interaction of growth stage x residue. At the low residue growth stage, milk production per cow was affected by the maturity stage, but with high residue and more mature alfalfa, cows compensated lower quality with higher selectivity and intake to maintain milk production. The highest milk production per ha was obtained with pre-bud and 10% flower stages, both with low post - grazing residues, reaching 8680 and 7225 kg milk ha^-1 for pre-bud and 10% flower, respectively for period I; and 7194 and 7790 kg milk ha^-1 for the same stages in period II. The treatments had no effect on milk composition. The continuous use of alfalfa at a pre-bud stage reduced re-growth capacity of alfalfa at the end of the growing season. According to forage composition before and after grazing, the animals showed a high capacity for selecting their forage.