Table 4.

Summarized results of the first difference-in-differences analysis (case herds changed from “BVDV not free” to “BVDV free”) for the effects on calving interval (days), gross margin (euros/kg milk/year), milk yield (kg/cow/year) and somatic cell count (1,000 cells/mL) of dutch dairy herds bovine viral diarrhea virus (BVDV)-free certification.

Effects	Categories	Calving interval		Gross margin		Milk yield		Somatic cell count
		Exponent of estimated coefficient	p-value	Exponent of estimated coefficient	p-value	Exponent of estimated coefficient	p-value	Exponent of estimated coefficient	p-value
Intercept		431	0.00	0.36	0.00	8,455	0.00	200	0.00
BVDV certification status	BVDV-free	Referent
	Not-freea	0.998	0.81	0.968	0.29	0.985	0.34	0.972	0.65
Herd size, n cows		1.000	0.52	1.001	0.35	1.000	0.75	0.999	0.72
Farm intensity, n cows/ha/year	Smallb	Referent
	Mediumb	1.005	0.25	0.993	0.82	0.984	0.34	0.949	0.27
	Largeb	0.991	0.27	0.981	0.57	0.978	0.27	0.917	0.13
Milk yield, kg/cow/year		1.000	0.07	1.000	0.15	–	–	–	–
Year	2014	Referent
	2015	1.000	0.99	0.746	0.00	1.014	0.11	0.905	0.00
	2016	0.990	0.47	0.656	0.00	1.030	0.01	0.953	0.27
	2017	0.992	0.58	0.941	0.23	1.065	0.00	0.880	0.00
	2018	0.984	0.29	0.907	0.06	1.072	0.00	0.823	0.00
	2019	0.978	0.14	0.887	0.03	1.058	0.00	0.774	0.00

^aThe not-free status refers to a herd that participated in the BVDV-free program but had not yet obtained the BVDV-free certification.

^bThe farm intensity variable consists of three categories: Small (n ≤ 1.6 Cows/ha/Year), Medium (1.6 < n ≤ 2.6 Cows/ha/Year), and Large (2.6 < n ≤ 5 Cows/ha/Year).