EFFECT OF DIETARY NEUTRAL DETERGENT FIBER CONCENTRATION AND FORAGE SOURCE ON PERFORMANCE OF LACTATING COWS

'Mott' dwarf elephantgrass, forage sorghum, 'Tifton 81' bermudagrass, and whole corn plant were stored as silage and fed as the only forage source in diets formulated to 31, 35, and 39% NDF. The 12 diets were f ed for ad libitum intake as a TMR to midlactation Holstein cows, prima rily to determine the effect of NDF concentration and forage source on DMI and milk production. Increased dietary NDF concentration linearly decreased DMI (3.69 to 3.35%) and OM intake (3.39 to 3.06%) as a perc entage of BW and linearly increased NDF intake as a percentage of BW ( 1.15 to 1.32%). Production of milk (23.0 to 21.7 kg/d) and 4% FCM (20. 7 to 19.6 kg/d) and percentage of milk protein (3.16 to 3.07%) decreas ed linearly as dietary NDF concentration increased. Cows fed dwarf ele phantgrass silage or corn silage, which were higher quality forage sou rces based on greater rates and extents of fiber digestion, consumed m ore DM and produced more milk than cows fed sorghum silage or bermudag rass silage. Cows fed diets containing sorghum silage had the lowest D MI and milk production. Apparent digestibility of NDF and ADF from cor n silage and dwarf elephantgrass silage was greater than that of sorgh um silage and bermudagrass silage. In addition to dietary NDF concentr ation, digestibility of dietary fiber influences DMI and milk producti on.