Forage Evaluation. II. Productive Response of First-Calf Holstein Heifers Fed Early-Cut or Late-Cut Alfalfa Hay as the Only Source of Energy Throughout a Total Lactation

Thirty-nine first-calf Holstein cows were fed early-cut or late-cut alfalfa hays as the only sources of energy for a 280-day lactation. Before calving, the animals had been used in a trial to determine the effect of feeding these two forages on growth rate. After parturition, half of the heifers on each prepartum forage were transferred to the opposite treatment to measure carry-over effects. Fourteen-day comparisons were made for three stages of lactation: Phase I, Periods 1-7; Phase II, 8-15; Phase III, 16-20. Switching hay treatments at calving time caused significant differences in milk production and rates of weight change in Phase I. All cows gained weight during the trial, even though milk production was below the estimated potential. Feed intake and milk production were greater and conversion ratios of hay to milk were higher for cows fed early-cut hay than for those offered late-cut hay. Milk from cows fed late-cut hay during both the pre-and postpartum treatments was significantly lower in percentage o fat and protein.