Table 7 Estimated hazard ratio from the multivariable Cox regression model with time at culling due to reproductive problems amongst only culled cows and herd as cluster

COD recorded during previous lactation

No

50,375

42,601

n.s

81,680

-

1.0

Yes

0

90

n.s

442

14.2

1.56 (1.24-1.97)

COD recorded during present lactation

No

50,173

-

1.0

42,288

-

1.0

81,169

-

1.0

Yes

202

11.9

1.38 (1.15-1.66)

403

45.3

1.68 (1.45-1.96)

953

178.3

2.06 (1.85-2.29)

Twins or triplets

No

49,927

n.s

41,302

-

1.0

78,539

n.s

Yes

448

n.s

1,389

4.8

1.15 (1.01-1.30)

3,583

n.s

Calving season

Spring

10,328

-

1.0

10,229

-

1.0

23,002

-

1.0

Summer

11,027

31.9

1.24 (1.15-1.35)

10,275

19.4

1.18 (1.10-1.27)

19,862

46.1

1.27 (1.18-1.36)

Autumn

16,890

1.1

1.04 (0.97-1.11)

12,597

1.8

1.05 (0.98-1.12)

23,706

8.0

1.10 (1.03-1.17)

Winter

12,130

2.8

1.06 (0.99-1.14)

9,590

0.5

1.02 (0.95-1.10)

15,552

2.7

1.06 (0.99-1.13)

Region

< 60° latitude

14,113

0.5

1.04 (0.94-1.15)

11,720

0.2

0.98 (0.88-1.09)

21,059

10.5

1.19 (1.07-1.33)

60 to 65 °

31,567

7.7

1.14 (1.04-1.25)

26,789

6.7

1.14 (1.03-1.26)

52,941

18.6

1.24 (1.12-1.36)

> 65 °

4,695

-

1.0

4,182

-

1.0

8,122

-

1.0