This study’s objective was to identify milk thermoduric microorganism population differences between compost bedded pack and deep sand bedded freestalls herds. Bulk tank milk samples were collected from herds housing cows exclusively on compost bedding (n = 10) or fresh sand bedding (n = 10) in the winter and summer of 2017. Three 9 mL bulk tank milk samples were pasteurized at 63°C for 30 min, 72°C for 15 s, or 135°C for 2 s. Fifty μL of milk was spiral plated on Plate Count Agar in duplicate. Plates were incubated at 35°C and 55°C for 24 h and 4°C for 10 d. A most probable number count was performed to determine growth <10 cfu/mL. Briefly, 1 mL milk was added to 3 tubes containing 9 mL Brain Heart Infusion Broth for each farm, pasteurization, and incubation combination. Inoculated broth was plated for isolation to determine growth. Morphologically unique colonies were isolated and identified using a Vitek 2 (bioMerieux, Hazelwood, MO, USA). Plate counts served as dependent variables and housing type as independent variables in a one-way ANOVA (Proc ANOVA, SAS v9.3; Cary, NC). Plate count results are shown in Table 1. Bacillus licheniformis was the only isolate from compost bedded pack milk. Bacillus coagulans, Bacillus licheniformis, Brevibacillus borstenlensis, and Paenibacillus polymyxa were isolated from sand bedded freestall milk. Compost bedding herds were not significantly greater than sand bedding herds in bulk tank milk thermoduric microorganisms. Future analysis will investigate bedding and teat skin thermoduric microorganism differences in bedding. Table 1. Results of a one-way ANOVA comparing milk thermoduric microorganism counts from compost bedded pack barn and sand bedded freestall barn herds

Temperature (°C)		Count (mean ± SD; cfu/mL)		F-value	P-value
Pasteurization	Incubation	Compost bedded pack	Sand freestall
63	4	2.0 ± 6.4	0.0 ± 0.0	1.0	0.33
	37	14.4 ± 17.6	10.3 ± 11.4	0.4	0.55
	55	2.5 ± 4.0	1.3 ± 1.1	0.9	0.36
72	4	0.0 ± 0.0	0.0 ± 0.0	—	—
	37	3.9 ± 4.8	15.8 ± 15.9	5.2	0.04
	55	5.2 ± 9.4	1.3 ± 0.9	1.7	0.20
135	4	0.0 ± 0.0	0.0 ± 0.0	—	—
	37	56.3 ± 136.9	25.7 ± 73.5	0.4	0.54
	55	0.0 ± 0.0	0.0 ± 0.0	—	—