Effects of forage source on chewing and rumen fermentation in lactating dairy cows

Abstract

The objective of this experiment was to evaluate the effects of partial replacement of corn silage with long alfalfa hay and/or coarse chopped wheat straw on chewing activity and rumen fermentation in late lactating dairy cows fed diets with 50% forage on dry matter basis. Twelve late lactating Holstein primiparous cows including four cows equipped with a rumen cannula, averaging 210 +/- 20 d in milk and weighing 575 +/- 50 kg were randomly assigned in a 4x4 Latin square design. During each of four 21-d periods, cows were fed 4 total mixed diets that varied in the forage sources : 1) CS (50% corn silage), 2) CSW (35% corn silage + 15% wheat straw), 3) CSA (35% corn silage + 15% alfalfa hay), 4) CSWA (25% corn silage + 10% wheat straw + 15 % alfalfa hay). The physically effective neutral detergent fiber (peNDF) contents of the diets which were determined by using the Penn State Particle Separator were as 33.2, 36.3, 33.6, and 35.3% of DM for CS, CSW, CSA, and CSWA diets, respectively. The proportion of particles retained on the 19.0 mm screen of the CS was lower (P < 0.001) than in the others group (3, 14, 12, and 24 % of DM, for CS, CSW, CSA, and CSWA diets, respectively). Dry matter intake was not affected by the diets but peNDF intakes were lower (P < 0.001) with CS and CSA than other diets. Cows spent more time eating the CSW, CSA and CSWA diets compared with CS diet (P < 0.001). Cows fed with CSW spent more time ruminating than cows fed CS diet (P < 0.05). Total chewing time was higher (P < 0.01) in CSW (662 min/d) and CSWA (633 min/d) groups than CS (521 min/d). Mean rumen pH values, ammonia content (NH3-N), acetate/propionate ratio, and total concentration of volatile fatty acids in the rumen fluid were not affected by the treatments. However, the time (h/d) where the pH was under 5.8 value, was increased when cows fed the CS diet (P < 0.001). It is concluded that forage source may have an effect on the chewing activity and rumen pH related to the peNDF and fiber structure. The proportion of particles > 19.0 turn and peNDF may be used as predictor of chewing activity.