Digestible Protein Requirements of Calves Fed High Energy Rations ad Libitum

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Abstract
Pelleted calf starter rations con-taining8.5 (R-l), 11.3 (R-2), and 12.5% (R-3) digestible protein were fed ad libitum to 3 treatment groups of 12 Holstein heifer calves from birth to 91 kg body weight (Period 1). The concentrate-to-roughage ratio was 80:20. A limited amount of milk was fed until weaning at 6 weeks of age. At 91 kg of body weight, the 36 calves were allotted by factorial arrangement to grain mixes containing 5.1 (R-A), 8.5 (R-B), and 9.1% (R-C) digestible protein to observe calf responses from 91 to 182 kg body weight (Period 2) and possible interactions with protein levels used in Period 1. Rolled grains and long alfalfa hay were separated, but offered ad libitum. Average daily gains during Period 1 (post-weaning values) were 0,72 (R-1), 0.72 (R-2), and 0.73 (R-3) kg, respectively; Period 2 gains were 1.12 (R-A), 1.09 (R-B), and 1.11 (R-C) kg. Average utilization of digestible energy [DE] by treatment groups were 9.48 (R-l), 8.52 (R-2), and 8.46 (R-3) megcal DE/kg gain (Period 1, post-weaning); 13.02 (R-A), 12.97 (R-B), and 13.69 (R-C) megcal DE/kg gain (Period 2). These differences were not significant (P( 0.05). Utilizations of digestible protein [DP] per unit of gain were 0.24 (R-l), 0.31 (R-2), 0.36 (R-3) kg DP/kg gain, Period 1; 0.29 (R-A), 0.39 (R-B), 0.45 (R-C) kg DP/kg gain, Period 2. These differences were all significant (P<0.05). Skeletal growth was unaffected by protein levels. No interaction effects on calf response were observed between protein levels of Periods 1 and 2. Protein consumption is compared to current feeding standards and theoretical requirements.