AbstractThree stargrass silage (SGS)-based diets formulated to contain 20, 26 and 32% neutral detergent fiber (NDF) were compared as to their effect on dry matter intake (DMI) and milk production. Twelve lactating Holstein cows averaging 110 days in milk were arranged in four replications of a 3 x 3 Latin Square design. Treatments did not affect DMI or DMI as percentage of body weight (BW); mean values for these parameters were 15.4 kg/cow/day and 3.06%, respectively. However, cows consuming 32% NDF diet had a tendency toward lower (8.6%) intake of organic matter (OM) as percentage of BW than cows on the 20% NDF diet. Intake of NDF as a percentage of BW increased (P < 0.01) linearly (0.62 to 0.93%) as dietary NDF concentration increased. Milk production averaged 21.0 kg/cow/day and was not affected by dietary treatment. Reducing dietary NDF from 32 to 20% resulted in a reduction (P < 0.01) in milk fat from 3.09 to 2.66%.This reduction resulted in a 1.3 kg/cow/day increase (P < 0.05) in 3.25% fat-corrected milk (3.25% FCM) as the percentage of dietary NDF increased. Gross efficiency of energy (NEL) use for milk production and 3.25% FCM increased linearly with dietary NDF by 9.7 and 17.3%, respectively. Results point out that for mid-lactation cows at the observed level of production, diets lower than 32% NDF will not result in higher DMI and milk production, and will be less efficient in the use of energy for milk production.
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