Effect of alfalfa maturity on fiber utilization by high producing dairy cows.

Six ruminally cannulated cows were used in a replicated 3 x 3 Latin square to study the effect of alfalfa maturity on utilization of DM and fiber. Cows were fed three diets based on alfalfa hay at early vegetative, late bud, or full bloom maturities. Forage:concentrate ratios were: 68:32, 53:47, and 45:55 for diets with early vegetative, late bud, and full bloom hays. Concentrations of NDF in the early vegetative and late bud diets was higher (32.6%) than NDF in the full bloom diet (27.9%) after accounting for feed refusals. Fat-corrected milk yield was similar, but fat percentage was higher for the diet with early vegetative hay than the diets with late bud or full bloom alfalfa. Dry matter intake was higher for the diet with early vegetative hay than the diets with late bud or full bloom hay (26.1, 24.4, and 24.8 kg/d). Ruminal dacron bag incubations of the three hays suggest that the high digestibility of the early vegetative hay was due to more soluble DM, more potentially digestible DM and fiber, and a faster rate of digestion. These factors compensated for the faster passage of the early vegetative hay and resulted in a higher intake and better utilization of DM and fiber.