The objectives of this study were to determine how feeding diets that differed in dietary neutral detergent fiber (NDF) concentration and in vitro NDF
digestibility affects dry matter (DM) intake, ruminal fermentation, and milk production in early
lactation dairy cows. Twelve rumen-cannulated,
multiparous Holstein cows
averaging 38 +/- 15 d (+/-
standard deviation) in milk, and producing 40 +/- 9 kg of milk daily, were used in a replicated 4 x 4
Latin square design with 28-d periods. Treatment diets were arranged in a 2 x 2 factorial with 28 or 32% dietary NDF (DM basis) and 2 levels of
straw NDF
digestibility: 1) LD, untreated
wheat straw (77% NDF, 41% NDF
digestibility) or 2) HD, anhydrous NH(3)-treated
wheat straw (76% NDF, 62% NDF
digestibility). All 4 diets consisted of
wheat straw,
alfalfa silage, corn silage, and a
concentrate mix of cracked corn grain, corn
gluten meal, 48%
soybean meal, and
vitamins and
minerals.
Wheat straw comprised 8.5% DM of the 28% NDF diets and 16% DM of the 32% NDF diets. Cows fed 28% NDF and HD diets produced more milk, fat, and protein than those consuming 32% NDF or LD diets. Dry matter intake was greater for cows consuming 28% NDF diets, but intakes of DM and total NDF were not affected by in vitro NDF
digestibility. Intake of
digestible NDF was greater for cows consuming HD diets. Ruminal fermentation was not affected by feeding diets that differed in NDF
digestibility. Ruminal NDF passage rate was slower for cows fed HD than LD. No interactions of dietary NDF concentration and in vitro NDF
digestibility were observed for any parameter measured. Regardless of dietary NDF concentration, increased in vitro NDF
digestibility improved intake and production in early
lactation dairy cows.
