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Table 3 Milk yield, milk chemical composition and gas emission of dairy cows, by lactation state

From: Mineral status and enteric methane production in dairy cows during different stages of lactation

  Lactation stage1 Statistics
Items Early Middle Late SEM P-value
Yield
 Milk, kg/d 50.43a 42.35b 31.31c 1.789 < 0.0001
 ECM,2 kg/d 45.69a 40.51a 31.65b 1.438 < 0.0001
 Fat, g/d 1720a 1544a 1232b 57.10 < 0.001
 Protein, g/d 1483a 1379a 1119b 43.90 < 0.001
 Casein, g/d 1170a 1089a 883.5b 34.97 < 0.001
 Lactose, g/d 2500a 2084b 1511c 91.36 < 0.0001
Milk composition
 Fat, % 3.425 3.665 3.931 0.5543 0.053
 Protein, % 2.943a 3.271b 3.580c 0.0646 < 0.0001
 Casein, % 2.322a 2.584b 2.824c 0.0526 < 0.0001
 Lactose, % 4.958 9.924 4.819 0.0293 0.130
 Dry matter, % 11.97a 12.48ab 12.96b 0.1228 < 0.01
 Urea, mg/L 225.2a 297.8b 326.6b 10.06 < 0.0001
 Somatic cells, 103/mL 91.5 100.0 126.6 18.61 0.084
 Urea/protein ratio 76.63a 91.32b 91.69b 2.339 0.007
Methane emission
 Methane production, ppm 606.9a 507.9b 471.2b 12.87 < 0.0001
 Methane yield, ppm/kg DMI3 20.40a 16.87b 15.84b 0.441 < 0.0001
 Methane intensity, ppm/kg ECM 13.45ab 12.47a 15.44b 0.457 0.020
CO2 production, ppm 5611a 4118b 4447ab 251.8 < 0.05
  1. a-cMean values in the same row with different superscripts are significantly different (P < 0.05), as determined by Tukey’s post-hoc test
  2. 1Early = early-stage lactation (1–100 days); Middle = middle-stage lactation (101–250 days); Late = late-stage lactation (> 250 days)
  3. 2ECM = energy-corrected milk
  4. 3DMI = dry matter intake