Growth performance of newborn dairy calves fed a milk replacer with 2 protein concentrations at 2 feeding rates

Objective: The objective was to evaluate the growth performance by calves fed a conventional milk replacer (MR) or modified accelerated MR (24% CP) to prevent the slump in postweaning calf starter intake and feed efficiency. Materials and Methods: A total of 104 (1 to 5 d old) Holstein heifer calves (39.3 +/- 0.66 kg) were assigned randomly to 1 of 4 MR treatments to evaluate preweaning (1 to 42 d) and postweaning (43 to 56 d) performance in a 2 x 2 factorial arrangement of CP concentrations [20% CP or 24% CP high protein (HP) with feeding rates (FR) of 0.57 or 0.68 kg/d]. Treatments were MR fed at 15% solids (as fed): (1) control (CP1): a 20% CP:20% fat MR fed at 0.284 kg 2x/d for 35 d; (2) CP2: the 20:20 MR fed at 0.34 kg 2x/d for 35 d; (3) HP1: a 24:20 MR fed at CP1 rate; and (4) HP2: the 24:20 MR fed at CP2 rate. Results and Discussion: No interactions of CP by FR were detected for growth parameters. During 1 to 14 d, calves fed higher MR FR (CP2 and HP2) had greater (P < 0.01) ADG (0.37, 0.44, 0.36, and 0.45 kg/d for CP1, CP2, HP1, and HP2, respectively) compared with calves fed lower MR FR (CP1 and HP1). Preweaning ADG (1 to 42 d) were similar (P > 0.10). Intakes of calf starter from 1 to 56 d were similar (P > 0.10) for calves fed MR with different CP concentrations (0.77 and 0.78 kg/d), whereas calf starter intake (0.81 and 0.74 kg/d) was reduced (P < 0.05) for calves fed higher MR FR. Feed conversions from 1 to 56 d were similar (P > 0.01) for calves fed different CP concentrations (0.54 and 0.55 kg/kg) but were improved when fed higher MR FR (0.53 and 0.56 kg/kg). However, a trend (P < 0.10) of CP by FR interaction from 43 to 56 d suggested that calves fed CP2 had greater feed conversions (0.46, 0.53, 0.46, and 0.49 kg/kg for CP1, CP2, HP1, and HP2, respectively). This suggests a carryover effect on postweaning performance for calves fed CP2. Implications and Applications: Feeding calves a conventional MR (20%CP:20% fat) at different FR with different CP concentrations resulted in similar performance. Feeding a higher CP MR (24% CP:20% fat) at higher FR did not affect preweaning gain of dairy calves.