welve lactating Friesian cows with the average body weight of 435-570 kg were used in this study. All animals in this study were in the 2 nd to 4 th lactation season were randomly distributed into four similar groups (three cows for each group). All groups were individually fed according to NRC (2001) recommendations. The four experimental rations were formulated as follows: control: 52% concentrate feed mixture (CFM) (40% corn grain, 30% wheat bran, 23% undecorticated cottonseed meal, 5% molasses, 0.5% salt and 1.5% limestone) + 20% corn silage (CS) + 28% rice straw (RS), experimental ration 1 (Exp.1): 52% CFM (35% corn grain, 30% wheat bran, 10% corn gluten feed (CG), 18% undecorticated cottonseed meal, 5% molasses, 0.5% salt and 1.5% limestone) + 20% CS + 28% RS, experimental ration 2 (Exp.2): 52% CFM (32.5% corn grain, 30% wheat bran, 15% CG, 15.5% undecorticated cottonseed meal, 5% molass, 0.5% salt and 1.5% limestone) + 20% CS + 28% RS and experimental ration 3 (Exp.3): 52% CFM (30% corn grain, 30% wheat bran, 20% CG, 13% undecorticated cottonseed meal, 5% molasses, 0.5% salt and 1.5% limestone) + 20% CS + 28% RS. Four digestibility trials were conducted to determine nutrients digestibility coefficients and nutritive values of the experimental rations. Each digestibility trial consisted of 15 days preliminary period followed by 7 days collected period. Results showed that the dry matter intakes (% body weight) were higher with feeding on Exp.1 or Exp.2 (3.38 and 3.51, respectively) than feeding on control or Exp.3 (3.25 and 3.26, respectively). The apparent digestibility of CP was significantly (P<0.05) higher with feeding on control (74.60%) than feeding on Exp.
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