Table 4.

Effect of pasture growth and day length on E. coli O157 shedding in a cohort of 52 dairy heifers; both effects were tested as continuous variables and also were collapsed into three categories for testing

Variable	Parameter	n	Estimate	s.e.	95% CI	P	OR
Pasture continuous	Constant		−0·435	0·091	−0·614 to −0·256	n.a.	1
	kg/ha per day		0·013	0·003	0·007 to 0·019	<0·001	1·013
Pasture categorical	No growth	322	−0·416	0·114	−0·639 to −0·193	n.a.	1
	Low pasture	230	0·046	0·176	−0·298 to 0·391	0·792	1·048
	High pasture	290	0·623	0·164	0·302 to 0·945	<0·001	1·865
Day length continuous	Constant		−5·40	1·75	−8·837 to −1·962	n.a.	1
	Minutes		0·006	0·002	0·002 to 0·010	0·01	1·005
Day length categorical	Short	148	−0·135	0·165	−0·458 to 0·188	n.a.	1
	Medium	262	−0·778	0·214	−1·197 to −0·359	<0·001	0·459
	Long	520	0·212	0·187	−0·154 to 0·578	0·256	1·237

s.e. Standard error; CI, confidence interval; OR, odds ratio; n.a., not applicable as the reference level.