Table 6 Estimated hazard ratio from the multivariable Cox regression model with time at culling as the dependent variable and herd as cluster. COD = cystic ovarian disease

COD recorded during previous lactation

No

197,900

-

-

144,464

-

1.0

199,409

-

1.0

Yes

0

-

-

256

3.7

1.22 (1.00-1.49)

952

18.7

1.22 (1.12-1.34)

COD recorded during present lactation

No

197,105

-

1.0

143,517

-

1.0

197,792

-

1.0

Yes

795

1.8

0.91 (0.80-1.04)

1,203

2.3

1.07 (0.98-1.17)

2,569

59.2

0.79 (0.75-0.84)

Twins or triplets

No

196,303

-

1.0

140,825

-

1.0

192,986

-

1.0

Yes

1,597

5.2

1.11 (1.02-1.22)

3,895

67.6

1.25 (1.19-1.32)

7,375

162.2

1.25 (1.20-1.29)

Calving season

Spring

38,384

103.7

1.17 (1.14-1.21)

33,772

2.9

1.03 (1.00-1.06)

54,731

4.3

1.02 (1.00-1.05)

Summer

47,907

-

1.0

35,491

-

1.0

48,959

-

1.0

Autumn

68,261

20.5

1.07 (1.04-1.09)

45,229

23.5

0.93 (0.91-0.96)

61,351

71.6

0.92 (0.90-0.93)

Winter

43,348

183.9

1.22 (1.19-1.26)

30,228

25.2

1.08 (1.05-1.11)

35,320

35.7

1.07 (1.05-1.10)

Herd size

< 35

165,420

-

1.0

121,395

-

n.s

169,781

-

n.s

35 to 84

30,489

7.9

1.06 (1.02-1.10)

21,834

-

n.s.

28,555

-

n.s.

> 84

2,047

0.4

1.06 (0.88-1.27)

1,536

-

n.s.

2,088

-

n.s.

Region

< 60° latitude

53,392

34.0

1.15 (1.10-1.20)

37,822

22.3

1.11 (1.06-1.16)

49,708

10.8

1.06 (1.02-1.09)

60 to 65 °

125,037

8.1

1.06 (1.02-1.11)

92,371

1.4

1.02 (0.99-1.06)

130,883

0.4

1.01 (0.98-1.04)

> 65 °

19,471

-

1.0

14,527

-

1.0

19,770

-

1.0