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Table 4 Logistic GEE model for the probability of a herd with an SCC ≤ 200,000 cells/mL

From: Insights into udder health and intramammary antibiotic usage on Irish dairy farms during 2003-2010

Variable

 

b

S. E.

p-value

OR

95% CI

Intercept

 

-0.72

0.04

< 0.001

0.49

0.45

0.52

Month

1

0.00

0.00

.

1.00

1.00

1.00

2

0.17

0.03

< 0.001

1.18

1.12

1.24

3

0.28

0.03

< 0.001

1.32

1.26

1.39

4

0.48

0.03

< 0.001

1.62

1.54

1.71

5

0.53

0.03

< 0.001

1.70

1.62

1.79

6

0.33

0.03

< 0.001

1.39

1.32

1.47

7

0.00

0.03

0.908

1.00

0.95

1.06

8

-0.04

0.03

0.133

0.96

0.91

1.01

9

-0.12

0.03

< 0.001

0.89

0.84

0.94

10

-0.29

0.03

< 0.001

0.75

0.71

0.79

11

-0.40

0.03

< 0.001

0.67

0.64

0.71

12

-0.29

0.03

< 0.001

0.75

0.71

0.80

Year

2004

0.00

0.00

.

1.00

1.00

1.00

2005

-0.15

0.02

< 0.001

0.86

0.82

0.90

2006

-0.19

0.03

< 0.001

0.82

0.78

0.87

2007

-0.06

0.03

0.036

0.94

0.89

1.00

2008

0.03

0.03

0.284

1.03

0.97

1.09

2009

-0.26

0.03

< 0.001

0.77

0.73

0.82

2010

-0.48

0.03

< 0.001

0.62

0.58

0.66

Herd sizea

Q1

0.00

0.00

.

1.00

1.00

1.00

Q2

-0.10

0.03

0.001

0.91

0.86

0.96

Q3

-0.15

0.03

< 0.001

0.86

0.81

0.91

Q4

-0.36

0.03

< 0.001

0.70

0.65

0.75

Spring calving

Non-Spring

0.00

0.00

.

1.00

1.00

1.00

Spring

-0.10

0.08

0.211

0.91

0.78

1.06

Spring × Monthb

Spring: 1

0.00

0.00

.

1.00

1.00

1.00

Spring: 2

0.47

0.07

< 0.001

1.61

1.39

1.86

Spring: 3

0.40

0.07

< 0.001

1.49

1.30

1.72

Spring: 4

0.38

0.07

< 0.001

1.46

1.27

1.68

Spring: 5

0.38

0.07

< 0.001

1.46

1.27

1.68

Spring: 6

0.42

0.07

< 0.001

1.53

1.33

1.76

Spring: 7

0.49

0.07

< 0.001

1.63

1.41

1.88

Spring: 8

0.46

0.07

< 0.001

1.58

1.37

1.83

Spring: 9

0.36

0.07

< 0.001

1.44

1.24

1.66

Spring: 10

0.14

0.07

0.056

1.15

1.00

1.33

Spring: 11

-0.27

0.08

0.001

0.76

0.66

0.89

Spring: 12

-0.37

0.09

< 0.001

0.69

0.58

0.83

Spring × Yearb

Spring: 2004

0.00

0.00

.

1.00

1.00

1.00

Spring: 2005

0.05

0.04

0.221

1.05

0.97

1.15

Spring: 2006

0.07

0.05

0.107

1.08

0.98

1.18

Spring: 2007

0.11

0.05

0.017

1.12

1.02

1.23

Spring: 2008

0.08

0.05

0.076

1.09

0.99

1.20

Spring: 2009

0.17

0.05

0.001

1.19

1.08

1.31

Spring: 2010

0.31

0.05

< 0.001

1.36

1.23

1.51

  1. a Herd size groups were based on the quartile of the herd size within each year
  2. b Non-Spring herds were the reference category and set to 0