Pre- and post-weaning performance and health of calves fed milk replacers with two protein concentrations and two feeding rates

Abstract Text: One-hundred eight (1 to 5 d old) Holstein heifer calves (39.3±0.66 kg) were randomly assigned to 1 of 4 milk replacers (MR) to evaluate pre- (d 1 to 42) and post- (d 43 to 56) weaning performance in a 2 x 2 factorial design of crude protein (CP) concentrations (20% (CP) and 24% (HP)) with feeding rates (FR; 0.57 (1) and 0.68 (2) kg/d). Treatments were MR fed at 15% solids of: 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.  All MR’s were fed at 1x/d from d 36 to weaning at d 42 with water and 18% CP texturized calf starter (CS) offered free choice through d 56.  No significant (P>0.10) interactions of CP by FR were detected for growth parameters.  During d 1 to 14, calves fed CP2 and HP2 had the greatest ADG (0.36, 0.44, 0.36, and 0.45 kg/d for CP1, CP2, HP1 and HP2, respectively) compared to calves fed CP1 and HP1, but the interaction was non-significant (P>0.10).  Pre-weaning ADG’s (d 1 to 42) were similar (P > 0.10).  Calves fed HP2 had numerically greatest overall ADG d 1 to 56 compared to calves fed CP1 and HP1 with CP2 being intermediate. Intake of CS from d 1 to 56 was similar (P>0.10) for calves fed MR with different CP concentrations (0.77 and 0.78 kg/d), while CS intake (0.81 and 0.74 kg/d) was reduced (P<0.05) for calves fed higher MR FR.  Feed conversions from d 1 to 56 were similar 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<0.11) of CP by FR interaction from d 43 to 56 demonstrated calves fed CP2 having greater feed conversions (0.46, 0.53, 0.46 and 0.49 kg/kg for C-, C+, HP-, and HP+, respectively) compared CP1, HP1 and HP2 calves.  Thus, indicating a carryover effect on post-weaning performance for CP2 calves.  The results demonstrate calves fed a conventional MR at different FR with different CP concentrations performed similarly. Calves fed higher CP MR at higher FR had numerically the greatest ADG.  

Keywords: Milk replacers, protein concentration, feeding rate