Table 1.

Crude univariate analyses between seroprevalence of BVL and farm factors in seven prefectures in Japan

Variable and level	Number of herds	Median (IQR1)	P2
Herd size
< 30 head	35	43.3 (13.3, 60.0)	0.514
30--49 head	25	53.33 (16.7, 63.3)
≥ 50 head	30	50.00 (26.7, 73.3)
Cattle introduced into the herd within one year
No	11	46.7 (27.3, 60.0)	0.286
Yes, self-bred cows only	33	52.2 (25.0, 78.0)
Yes, including purchased cows	46	45.0 (13.3, 65.0)
Housing conditions
Tie housing	68	41.9 (13.3, 62.5)	0.001*
Loose housing	22	65.0 (52.2, 78.3)
Availability of own grazing area
Yes	65	43.3 (13.8, 63.3)	0.048*
No	25	52.2 (33.6, 78.0)
Presence of horseflies in summer
Never to seldom	28	26.7 (13.3, 51.8)	0.002*
Sometimes to often	29	47.6 (15.8, 65.0)
Very high	33	63.3 (44.4, 83.0)
Animal dehorning
Yes	58	60.0 (39.2, 73.3)	< 0.001*
No	32	20.0 (8.8, 43.0)
Plastic sleeve used for rectal palpation
One sleeve per cow	73	43.3 (14.5, 68.3)	0.012*
One sleeve for more than one cow	17	60.0 (47.8, 75.0)
Needle used for vaccination
One needle per cow	86	46.7 (16.7, 65.5)	0.100*
One needle for more than one cow	4	64.4 (50.5, 91.7)
Colostrum feeding
No	7	76.7 (60.0, 95.7)	0.003*
From dam to calves	63	42.1 (13.3, 60.0)
Pooled	20	50.0 (36.7, 75.8)
Overall	90	48.1 (17.1, 68.5)

¹Interquartile range

²Mann--Whitney U-test for two-level variables or Kruskal--Wallis test for all others

*Incorporated into multivariate model

Results of the Mann--Whitney U-test or the Kruskal--Wallis test showed that cattle housing conditions, availability of own grazing area, presence of horseflies in summer, dehorning, use of a plastic sleeve for rectal palpation, not changing needles between animals during herd vaccination, and colostrum feeding were possibly associated with seroprevalence (p < 0.15). These seven variables were incorporated in the multivariate model.