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Eight Holstein calves (44 ± 1 kg BW at birth) implanted with ruminal cannulaes (20 mm ID) at d 7 ± 1 after birth were used to investigate the effects of milk allowance on concentrate intake and ruminal fermentation patterns. Calves were allocated to one of four treatments (3.0, 4.7, 6.4 or 8.1 L skim-milk-based milk-replacer/d; 130 g solids/L milk). All calves had free access to a barley-based starter concentrate (319 g starch/kg), artificially-dried hay, and water. Ruminal samples were collected every 2 h for 24 h at wk 2, 3, 4, and 5. Ruminal pH was measured immediately and ruminal fluid was stabilized with metaphosphoric acid for later analysis. Concentrate intake was affected by a treatment times wk interaction (P < 0.01). The smallest concentrate intake was found with 6.4 L milk/d (17 g/d in wk 2 increasing to 389 g/d in wk 5) and the greatest concentrate intake was found with 3.0 L milk/d (310 g/d in wk 2 increasing to 1,601 g/d in wk 5 [SEM = 150]). Daily gain from wk 2 to 5 (714 ± 35 g/d) was not affected (P = 0.49) by treatment. The average (5.8 ± 0.1) and the minimum (5.4 ± 0.1) ruminal pH within a sampling period were not affected (P > 0.24) by treatment or wk. Hours/d with ruminal pH below 6.2 (18 ± 2 h/d), 5.8 (14 ± 2 h/d), and 5.4 (6 ± h/d) were not affected (P > 0.18) by treatment or wk. The total VFA concentration was affected by week (P < 0.01) and increased from 71 ± 9 mmol/L in wk 2 to 133 ± 9 mmol/L in wk 5. All data for calves with concentrate intakes above 25 g/d showed no relationship between concentrate intake level and severity of ruminal environment. The implication is that starch-based concentrates in general might be harmful to the juvenile rumen of milk-fed calves and more attention should be paid to formulating rumen-friendly starter concentrates. [ABSTRACT FROM AUTHOR]