Table 2.

Local transmission rate, PIntroLocal, per three month time period in the four different categories of herds, in a study estimating the probability of freedom from BRSV- and BCV antibodies in dairy herds located in two counties in western Norway. PIntroLocal was estimated from the proportion of herds that went from antibody- negative to positive during the study period (2013–2016) and did not purchase livestock.

Herd size	PIntroLocal
	BRSV		BCV
	Northern county	Southern county	Northern county	Southern county
Small herds	0.025	0.015	0.019	0.0078
Large herds	0.028	0.016	0.022	0.0087