Table I.

Descriptive statistics for sources of Staphylococcus aureus isolated in a dry-cow antibiotic efficacy field trial in eastern Canada in 1999–2000

	Number or score
Variable	Total or mean	Range or s	Prince Edward Island	Quebec	Ontario
Herds	40		3	16	21
Cows per herd	64	27–168	142	48	78
Cows enrolled	92		5	45	42
Lactations	2.9	1–8	2.8	3.0	2.8
Dry-period length (d)	66	18.5	71.8	65.3	66.3
Last LS before dry-off (and 95% CI per region)	5.7	1.3	6.2	5.9	5.4
Infected quarters	121		(5.1 to 7.3)	(5.6 to 6.2)	(5.0 to 5.7)
Infected per cow	1.3		5	65	51
DCT with tilmicosin	53		1.0	1.4	1.2
DCT with cloxacillin	68

s — standard deviation; LS — linear somatic cell count score, from Dairy Herd Improvement test; CI — confidence interval; DCT — intramammary dry-cow antibiotic therapy administered at dry-off