The objective of this study was to determine bedding and milking management practices associated with bulk tank (BT) quality (SCC and TBC), on large Wisconsin dairy farms. Ninety percent (325 of 360) of Wisconsin dairy farms producing in excess of 11,340 kg of milk daily participated in a personally administered survey consisting of 60 scripted questions. Milk quality test results were obtained from milk marketers for a 2-year period for 255 farms. Results were analyzed for 230 farms using the same bedding type (IB = Inorganic, MB = Manure solids, OB = Other organic) in all pens during the entire study period. Farms milked between 270 and 8,100 cows (mean = 908), selling an average of 33,714 kg daily. Farms which herd tested (n = 204) had an average RHA of 12,831 kg (IB), 11,746 kg (MB), or 11,973 kg (OB). The relationships between bulk tank somatic cell score (BTSCS), bedding type, and management practices were analyzed in a repeated measures model using PROC MIXED (SAS 9.4). Bulk tank SCS was least in the winter and spring, intermediate in the fall, and greatest in the summer with seasonal differences decreasing with increasing farm size (P < 0.001). Farms using Iodine based postdip had greater BTSCS than those using other postdips (P = 0.011) and BTSCS was lower on farms drying teats and wiping off predip than on those not drying teats (P < 0.001). Farms with a WMP using MB had a greater BTSCS than those using IB or OB. The SCS for farms without a WMP was less for herds using IB as compared with herds using OB (P < 0.05). Bulk TBC did not vary seasonally (Tukey adjusted P > 0.2) or among bedding types (Tukey adjusted P > 0.75). Table 1. Bulk tank SCS and SCC among farms with differing bedding types and presence of written milking protocols (WMP)

WMP	Bedding	n	SCS	SE SCS	SCC (×103)
Yes	Inorganic	122	4.06b	0.08	210b
Yes	Manure	17	4.55c	0.14	293c
Yes	Other organic	31	4.09b	0.11	213b
No	Inorganic	34	3.76a	0.10	169a
No	Manure	8	3.87ab	0.16	183ab
No	Other organic	18	4.30bc	0.13	245bc

^abcResults with different superscripts within column differ (Tukey adjusted P < 0.05).