Table 3.

Details of associations between management variables and seroprevalence to BCV, BRSV or both as estimated using a logistic regression model^a

Variablec	Level	Serological statusb, number of samples		Results from logistic regression model
		+	−	Odds ratio (OR)	95% CId of OR	P-value
Organic	Yes	317	24	0.11	0.02;0.53	0.006
	No	355	3	Reference
AIFe	Yes	435	10			nsf
	No	237	17
Stall type	Tie	300	8			ns
	Free	372	19
Weeks at pasture	Above median	304	19			ns
	Below median	368	8
Milk yieldg	Above median	320	6			ns
	Below median	344	21
Herd sizeg	Above median	377	17			ns
	Below median	287	10
Number of veterinary visits	Above median	343	19			ns
	Below median	329	8
Year of sampling	2005	326	12			ns
	2006	346	15

^aClustering of observations within herds is taken into account. Pearson χ² statistic = 149.5, df = 78.

^bAnimals seropositive to either BCV or BRSV or to both are denoted ‘+’, those seronegative to both are denoted ‘−’.

^cAll variables offered to the multivariable logistic regression model.

^dConfidence interval.

^eAI was performed by farm personnel rather than by professional AI technicians.

^fns: not significantly (P > 0.05) associated with serological status in the logistic regression model.

^gOne herd had missing information.