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

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