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Table 5 Additive genetic (σ 2 a ), animal permanent environmental (σ 2 pe ), residual (σ 2 e ) variances and heritability (h2) of the test-day records of milk yield (Kg) for some selected days in milk and different milking frequency

From: Influence of milking frequency on genetic parameters associated with the milk production in the first and second lactations of Iranian Holstein dairy cows using random regression test day models

Variances Days in milk (DIM)
5–35 36–65 66–95 96–125 126–155 156–185 186–215 216–245 246–275 276–305
Lact 1 (3X)
σ 2 a 5.0 5.7 4.9 5.2 6.1 8.1 9.1 8.0 8.5 21.7
σ 2 pe 9.2 11.0 11.7 11.3 11.9 13.4 15.2 17.8 20.0 18.1
σ 2 e 11.4 10.0 9.1 8.5 9.4 8.5 8.9 9.2 7.5 7.7
h 2 0.20 0.21 0.19 0.21 0.22 0.27 0.27 0.23 0.24 0.46
Lact 2 (3X)
σ 2 a 4.0 4.1 6.3 6.8 7.3 9.9 14.0 16.4 14.7 12.3
σ 2 pe 25.5 21.7 22.3 24.2 25.6 25.7 25.1 25.4 29.3 40.9
σ 2 e 20.9 19.0 15.7 14.3 13.4 12.7 12.5 11.5 11.2 10.1
h 2 0.08 0.09 0.14 0.15 0.16 0.20 0.27 0.31 0.27 0.19
Lact 1 (4X)
σ 2 a 10.1 8.9 12.0 11.6 11.5 11.2 11.0 9.5 9.1 13.5
σ 2 pe 20.3 14.3 11.6 10.7 10.6 10.9 11.4 12.7 15.6 21.6
σ 2 e 8.9 9.5 8.6 8.3 8.5 7.3 7.8 6.0 6.5 6.0
h 2 0.26 0.27 0.37 0.38 0.38 0.38 0.36 0.34 0.29 0.33
Lact 2 (4X)
σ 2 a 16.6 12.0 10.4 10.0 8.7 10.2 14.4 16.6 19.2 15.5
σ 2 pe 18.5 25.0 27.2 26.9 26.1 25.8 25.8 25.9 27.6 37.2
σ 2 e 21.6 16.4 15.2 11.6 12.3 11.4 8.9 8.0 7.9 6.7
h 2 0.29 0.23 0.20 0.21 0.18 0.22 0.29 0.33 0.35 0.26