Bacillus species offer advantages as direct-fed microbials (DFMs) because their spores tolerate the harsh environment of the gastrointestinal tract and some strains can produce enzymes such as xylanase which breaks down xylan and the bonds that link lignin to cellulose, potentially increasing dietary fiber digestibility. This study aimed to investigate the effects of Bacillus pumilus 8G-134 (BP) supplementation on performance of primiparous dairy cows fed low (20%, LS) or high (27%, HS) starch diets from calving to 112 DIM. We hypothesized that BP would improve total-tract nutrient digestibility and performance of cows fed LS or HS diets postpartum. Forty-eight (n = 12/treatment) primiparous cows were assigned to a common prepartum diet 42d before expected calving date. 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 5 × 10⁹ cfu/cow/day until 112 DIM. Factors combined produced 4 treatments: LS+carrier (LSCO); LS+BP (LSBP); HS+carrier (HSCO); HS+BP (HSBP). Fecal samples collected on d 7, 14 were analyzed for NDFd. Data were analyzed using the MIXED procedure of SAS. Apparent total-tract NDFd was greater (P = 0.05) for diets supplemented with BP, by 4.4% (LS) and 8.5% (HS) which tended to increase milk yield, 3.5% FCM and 3.5% ECM by 13.9%, 14.9% and 15.2% for HS diets, but increases in LS supplemented diets were less apparent. The 112 d of BP supplementation increased DMI and milk fat yield, and tended to improve yields of 3.5% FCM and milk protein. Results indicated that BP supplementation to primiparous cows can increase fiber digestibility and milk yield resulting in potential increases in profitability. Table 1. Intake and lactation performance

Item (kg/d)	Treatments					SEM	P-value
LS			HS
CO	BP	CO	BP	S	BP	S × BP
28 DMI
DMI	15.27	16.15		14.23	15.08	0.90	0.16	0.25	0.98
Milk	27.96	28.30		25.92	29.52	1.21	0.73	0.10	0.18
3.5% FCM	28.07	28.57		25.75	29.60	1.24	0.60	0.08	0.17
3.5% ECM	28.33	28.80		26.03	29.99	1.24	0.66	0.08	0.16
112 DMI
DMI	18.97	20.58		18.85	20.30	0.94	0.73	0.01	0.89
3.5% FCM	31.63	33.00		30.87	33.62	1.71	0.95	0.06	0.51
Milk fat	1.10	1.15		1.06	1.18	0.07	0.87	0.04	0.42
Milk protein	0.97	1.03		1.00	1.07	0.04	0.30	0.06	0.92