The solid diet of calves is the main determinant for ruminal development. It must contain high digestible ingredients, however with adequate level of fiber to maintain ruminal health. However, levels of NDF for calf starters are still controversial. Forty males and female calves Holstein newborns were blocked according to sex and birth weight and distributed in 3 treatments: (1) conventional calf starter (16% NDF); (2) high fiber calf starter (25% NDF), with soybean hulls replacing part of the corn; and (3) conventional calf starter (16% NDF) plus free access to grass hay. Animals received 4 L/d of milk replacer (MR) until gradual weaning at 56 d. Calves were weighed weekly and feed intake was recorded daily. The solid diets with higher levels of NDF did not negatively affect the starter or total solid diet intake nor the performance (P > 0.05). Daily gains are in agreement with NRC (2001) prediction for calves receiving 4 L/d of MR. All performance data were affected by the age of the calf (P < 0.05). Fecal score and pH were not affected (P < 0.05). These results show that solid diets with lower corn inclusions and consequently lower starch contents can result in similar weight gain as observed for conventional diets. Free access to hay did not reduce feed intake, leading to similar weight gain among groups with or without access to hay. Increasing the NDF of calf starter from 16 to 25%, including a high quality fiber source, have not reduced calves’ performance. Table 1. Performance of calves fed diets with different fiber contents

Item	Treatment			SEM	P-value1
16 NDF	25 NDF	HAY	T	A	T × A
Starter intake, g/d	319.9	435.0	305.3	61.07	0.27	<0.0001	0.045
Hay intake, g/d	—	—	18.6	5.99	—	0.007	—
Solid diet intake, g/d	322.5	435	321.6	60.72	0.32	<0.0001	0.044
Initial BW, kg	35.6	37.3	37.7	1.33	0.21	—	—
Final BW, kg	53.8	58.3	54.9	2.38	0.21	—	—
BW gain, g/d	308.8	350.2	314.1	35.24	0.59	<0.0001	0.868
Fecal score	2	1.9	1.9	0.11	0.83	<0.0001	0.799
Fecal pH	6.8	6.7	7.0	0.12	0.18	0.607	0.349

¹T = treatment effect; A = age effect; T × A = treatment vs. age effect.