Strains of Bacillus pumilus, a spore-forming gram-positive bacterial species can be highly resistant to environmental stresses and have the potential to produces xylanase. Xylanase increases fiber digestion and feed efficiency which might benefit cows during early lactation. This study aimed to investigate the effects of low (20%, LS) or high (27%, HS) dietary starch concentration and Bacillus pumilus 8G-134 (BP) supplementation during early lactation. We hypothesized that BP would increase DMI and milk yield of cows fed LS or HS diets postpartum. Forty-four (n = 11/treatment) multiparous cows dried-off 42d before expected calving date were assigned to a common prepartum diet. At calving, cows were fed a LS or HS lactation diet and BP carrier or BP was top dressed on the TMR once daily to provide 5x10⁹ cfu/cow/day until 112 DIM. Factors combined produced 4 treatments: LS+carrier (LSCO); LS+BP (LSBP); HS+carrier (HSCO); HS+BP (HSBP). Blood samples collected on d 7, 14, 21 and 28 after calving were analyzed for NEFA and BHBA concentrations. Data were analyzed using the MIXED procedure of SAS. No changes were observed on postpartum DMI and 3.5%FCM yield; however, NEFA was lower and BHBA tended to be lower in serum of BP vs. Control. Results indicated that BP supplementation during early lactation decreased body lipid mobilization. We hypothesize that greater amounts of digestible energy available from fiber digestion might have caused lower lipid mobilization in cows fed BP. Future research should further investigate the use of BP as a feed additive because it appears to modify blood metabolite concentrations in early lactation. Table 1. Body condition, lactation performance, and blood metabolites in early lactation

Item	Treatment					SEM	P-value
LS			HS
CO	BP	CO	BP	S	BP	S × BP
DMI, kg/d	18.34	18.68		17.18	19.86	0.80	0.16	0.25	0.98
EB, Mcal/d	−10.66	−10.18		−9.29	−7.52	1.83	0.25	0.51	0.71
3.5% FCM, kg/d	39.98	39.87		40.72	42.25	1.78	0.35	0.67	0.62
NEFA, µEq/L	363.95	311.66		475.85	314.84	68.80	0.29	0.05	0.33
BHBA, mg/dl	12.76	10.27		14.52	8.02	2.57	0.92	0.07	0.41