In the last 15 years there has been a +28% increase in milk production (33.9 to 39.5 kg/cow/d), a 12% decrease in total-tract feed passage rate (9.72 to 8.52 h) and a 1% decline in DM digestibility (66.02 to 65.12). This study examined the dairy cow performance by feeding B-complex vitamins in addition to vitamins A, D₃ and E. A total of 935 Holstein cows were used in a randomized complete block design with cow as the experimental unit, treatment as the fixed effect, and block as the random effect (187 cows × 5 treatments). Cows were blocked by age, reproductive and productive performance and were fed corn/corn silage diets formulated to meet or exceed 2001 NRC recommendations. Treatments were T1 = vitamins A/D₃/E, T2 = A/D₃/E/riboflavin, T3 = A/D₃/E/riboflavin/niacin, T4 = A/D₃/E/riboflavin/niacin/choline and T5 = A/D₃/E/B complex (Table 1). Bulk SCC (T1 = 170.3, T2 = 167.1, T3 = 163.5, T4 = 164.1 and T5 = 162.2 cell/mL, P = 0.03, respectively); days dry (57.0, 56.9, 56.2, 55.3, and 55.6 d, P = 0.04, respectively); incidence of clinical mastitis (16.4, 16.2, 16.0, 15.7, and 15.8%, P = 0.03, respectively); conception rate of first service (53.2, 53.8, 54.7, 55.1 and 56.0%, %, P = 0.03, respectively); conception rate, all services (49.1, 50.6, 51.2, 51.7 and 52.3%, P = 0.02, respectively); peak milk, first lactation (41.5, 40.9, 42.5, 43.4 and 44.3 kg, P = 0.02, respectively), peak milk, third lactation (59.7, 60.2, 63.4, 64.7 and 65.6 kg, P = 0.02, respectively); milk fat (3.86, 3.85, 3.52, 3.51 and 3.53%, P = 0.04, respectively) and milk protein (3.20, 3.24, 3.32, 3.39 and 3.40, P = 0.03, respectively). In conclusion, riboflavin, riboflavin/niacin, riboflavin/niacin/choline and all B-complex vitamins significantly increased productive and reproductive dairy cow parameters. Table 1 (Abstr. 336). Vitamins for 658-kg cow BW

Vitamin1	Unit/hd/d	Dry	Fresh	Lactation
A	IU	151,800	279,330	258,750
D3	IU	35,000	60,750	45,000
E	IU	3,000	4,000	2,561
Riboflavin	mg	500	1,000	1,000
Niacin	mg	3,000	6,000	6,000
Choline	mg	7,000	15,000	15,000
Thiamine	mg	0	240	120
Pyridoxine	mg	0	135	66
Biotin	mg	0	243	180
B12	mg	0	225	135
Pantothenic acid	mg	0	330	240
Folic	mg	0	255	201

¹B vitamins were coated.