Effect of forage physical form on chewing activity, dry matter intake, and rumen function of dairy cows in early lactation.

To examine the effects of reducing forage particle size on production, chewing, and digesta kinetic parameters in early lactation, 42 Holstein cows (9 ruminally cannulated) were assigned 14 d postpartum to one of three experimental diets with concentrate: alfalfa haylage: alfalfa pellets ratio of A) 60:40:0;B) 60:28:12; and C) 60:12:28 on a DM basis. The trial ran through the 12th wk postpartum, and measurements of chewing activity and rumen parameters were made during the 4th, 8th, and 12th wk postpartum. Dry matter intake (kg/d), milk production (kg/d), and milk fat percentage for diets A, B, and C were 23.1, 23.0, 18.8; 33.7, 35.5, 31.8; and 3.1, 2.9, 2.6, respectively. Rumen parameters and chewing activities were linearly related to haylage in the diet. Ruminal fluid dilution rate (%/h), volume (L), and outflow (L/d), rumination (min/d), total chewing (min/d), total chewing (min/kg DM intake), ruminal acetate (molar %), and NDF digestibility (%) were 16.6, 13.8, 10.0; 62, 58, 54; 243, 193, 137; 437; 367, 204; 649, 566, 376; 28.2, 24.1, 20.0; 58.6, 56.3, 53.8; and 32, 37, 23, respectively. These results suggest that dairy cattle in early lactation require a minimum amount of effective fiber to optimize production and intake. This requirement was met when 28%, but not 12%, of dietary DM was alfalfa haylage.