Table 6.

Results from the multivariable logistic regression analysis of factors associated with being a cow newly or chronically infected with subclinical mastitis in 578 dairy cows from 262 Swedish dairy herds (r2 = 00.6)

Variable	β	SE(β)	ORa	95% CIb (ORa)	P-value
Intercept	-0.17	0.17	-	-	-
Bacteriological finding
1: No bacterial finding	Ref.c	-	-	-	-
2: Staphylococcus aureus	0.71	0.27	2.03	(1.17; 3.52)	0.01
3: Coagulase-negative	0.17	0.27	1.18	(0.68; 2.06)	0.55
staphylococci
4: Streptococcus	0.82	0.33	2.27	(1.12; 4.60)	0.02
dysgalactiae
5: Streptococcus uberis	1.02	0.35	2.78	(1.38; 5.62)	0.004
6: Escherichia coli	0.67	0.58	1.95	(0.68, 5.62)	0.21
7: Other bacteria	0.63	0.38	1.87	(0.88; 4.00)	0.11
8: Contaminated	0.002	0.27	1.00	(0.58; 1.72)	0.99
Days in milk (centered)	0.005	0.0009	n.a.d	n.a.d	n.a.d
Days in milk (squared)	-0.00001	0.000004	1.56e	1.33; 1.83	0.006

^aOR = odds ratio

^bCI = confidence interval

^cRef. = reference category

^dn.a. = not applicable

^eOdds ratio is calculated for an interquartile increase from the mean in days in milk (85.5 DIM) in both DIM (centered) and DIM (squared)