VALUE OF ORCHARDGRASS AND ALFALFA SILAGES FED WITH VARYING AMOUNTS OF CONCENTRATES TO DAIRY-COWS

Orchardgrass was fertilized with 75 kg N/ha five times during the growing season, harvested at an immature stage (primary growth cut in late vegetative stage and regrowth cut every 25 to 28 d), and ensiled. Alfalfa was harvested in late bud to early flower stage and ensiled. Orchardgrass had 52% NDF and 22% CP, and alfalfa contained 40% NDF and 22% CP. The silages were fed in diets containing 20, 40, or 60% concentrate (DM basis) to midlactation cows. Few interactions between forage type and concentrate amount were found. Forage type did not affect milk production (24 kg/d) or composition, but cows fed alfalfa consumed more DM than those fed orchardgrass (22 vs. 20 kg/d). Increasing concentrate from 20 to 40% increased milk production, but no additional response was observed when it increased to 60%. Milk fat percentage was reduced when diets contained more than 20% concentrate, so production of FCM was not affected by amount of concentrate. Increasing amount of concentrate in the diet linearly increased DMI. Digestibility of DM was higher for orchardgrass than for alfalfa diets (67 vs. 63%). Digestibility of orchardgrass NDF was much higher than for alfalfa (72 vs. 48%). Concentrate did not affect DM or fiber digestibilities. High quality orchardgrass was similar in feeding value to high quality alfalfa. Feeding more than 40% concentrate did not improve the nutritional value of these diets.