Protein Concentrations for Starters Fed to Transported Neonatal Calves

Six trials were conducted to evaluate the performance of 292 Holstein bull calves (40 to 43 kg average initial BW; less than 7 d old) fed starters with various CP, rumen undegraded protein (RUP), and metabolizable protein (MP) concentrations. Calves were fed either 20% CP and 20% fat milk replacers (MR) at 454 g/d or 26% CP and 17% fat MR at 680 g/d and weaned at either 28 or 42 d. Starter and water was fed free-choice and measurements collected for 56 d. Trials 1, 2, 3, and 4 compared CP concentrations from 15 to 26% CP (as-fed basis). Trial 5 compared 18% CP starters with either A) low RUP, low MP or B) high RUP, high MP that had similar amino acid concentrations. Trial 6 compared A) a control starter, B) a high MP starter, and C) a high MP starter with equal rumen degradable protein as Starter A. There were no differences (P > 0.10) among treatments for any measurements in trials 1, 3, 4, 5, and 6 when starters that were 18% CP or greater were fed or when RUP and MP were altered. In trial 2, the effects of increasing starter CP from 15 to 21% were quadratic (P < 0.05) from 0 to 56 d, indicating 15% CP was inadequate. Also in trial 2, calves weaned at 28 d consumed more starter from 0 to 56 d, but ADG were not different (P > 0.15) than for calves weaned at 42 d. All 6 trials were simulated using the NRC (2001) calf submodel. In each case, energy, not CP, was predicted to limit gains, and observed gains were 109 to 138% of model predictions. Calf ADG, intake, efficiency, hip width change, or body condition score change did not improve when calves were fed starter with more than 18% CP when fed as either a conventional 20% CP, 20% fat MR fed at 454 g/d or a 26% CP, 17% fat MR fed at 680 g/d.