We hypothesized that pantothenic acid reduces the absorption of biotin in lactating dairy cows. Twenty-four Holstein cows (8 primiparous and 16 multiparous) were assigned to a 4 × 4 replicated Latin square design with 18-d periods. Cows were 109 ± 30 d in milk and weighed 591 ± 70 kg at the beginning of the experiment. Treatments consisted of a control diet (CON) containing 53% concentrate and 47% forage, CON supplemented with 20 mg/d biotin (BIO), CON supplemented with 475 mg/d pantothenic acid (PAN), and CON supplemented with 20 mg/d biotin + 475 mg/d pantothenic acid (BIOPAN). Data were analyzed with a Proc Mixed model that included the effects of square (fixed, 5 df), treatment (fixed, 3 df), treatment × square interaction (fixed, 15 df), period (random, 3 df), cow within square (random, 18 df), and the residual error (51 df). No differences among treatments were observed for dry matter intake (P < 0.46), milk yield (P < 0.68), fat concentration (P < 0.85) and yield (P < 0.88), protein concentration (P < 0.28) and yield (P < 0.07), lactose concentration (P < 0.90) and yield (P < 0.25), and milk urea nitrogen (P < 0.49). Biotin supplementation increased the concentration of avidin-binding substances (ABS) in milk (P < 0.03). This increase was similar for BIOPAN (P < 0.01). Relative to CON, pantothenic acid did not reduce the concentration of ABS in milk (P < 0.99). In conclusion, under the conditions of this experiment, pantothenic acid did not affect the absorption of biotin in lactating dairy cows. Table 1. Effect of biotin and pantothenic acid supplementation on performance and concentration of avidin-binding substances (ABS) in milk of dairy cows

Item	CON	BIO	PAN	BIOPAN	SEM	P <
DMI, kg/d	21.6	21.5	21.2	21.1	0.49	0.46
Milk yield, kg/d	41.9	41.9	42.1	41.1	1.41	0.68
Fat, %	2.83	2.79	2.88	2.90	0.19	0.85
Fat, kg/d	1.18	1.18	1.22	1.18	0.08	0.88
Protein, %	3.01	3.07	3.03	3.04	0.06	0.28
Protein, kg/d	1.26	1.31	1.30	1.25	0.04	0.07
Lactose, %	4.88	4.90	4.89	4.89	0.04	0.90
Lactose, kg/d	2.06	2.09	2.11	2.02	0.07	0.25
MUN, mg/dL	15.39	15.83	15.42	15.73	0.58	0.49
ABS in milk, ng/mL	28.9b	39.6a	28.9b	43.0a	3.36	0.01