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Table.8 Estimations of dietary calcium (Ca) requirements of broilers from 1 to 21 days of age based on the best fitted broken-line or quadratic models

From: Dietary calcium requirements of broilers fed a conventional corn-soybean meal diet from 1 to 21 days of age

Dependent variable Regression equationa R2 P-value Dietary Ca requirements, %
Serum ALP activity Y1 = 79.44–79.44X (0.59 ≤ X ≤ 1.00) Y2 = − 670.1 + 999.9X (1.00 ≤ X ≤ 1.18) 0.49 < 0.0001 1.00
Tibia ash percentage Y1 = 44.895 + 6.5766X (0.59 ≤ X ≤ 0.93) Y2 = −55.9373 - 5.3306X (0.93 ≤ X ≤ 1.18) 0.29 0.005 0.93
Tibia ALP activity Y1 = 668.4286–473.9648X (0.59 ≤ X ≤ 0.80) Y2 = 134.7242 + 193.1789X (0.80 ≤ X ≤ 1.18) 0.27 0.007 0.80
Tibia breaking strength Y1 = 11.0110 + 145.1498X (0.59 ≤ X ≤ 0.88) Y2 = 162.1505–27.2524X (0.88 ≤ X ≤ 1.18) 0.37 0.0005 0.88
Tibia BMD Y = 0.0285 + 0.2592X - 0.1400X2 0.24 0.005 0.93
Tibia ALP protein expression level Y = −0.6983 + 4.0791X - 2.2713X2 0.14 0.021 0.90
Middle toe BMD Y = −0.0341 + 0.2024X - 0.1153X2 0.46 < 0.0001 0.91
  1. aRegression equations based on the analyzed Ca concentrations (%) in the diets
  2. bAbbreviations: ALP alkaline phosphatase, BMD bone mineral density