Abstract
Four protein (CP) (9.0, 11.5, 14.5 and 17.5%) and three acid detergent fiber (ADF) (11, 18 and 25%) percentages were evaluated in a complete factorial experiment. Five calves were randomly assigned to an experimental ration at 8 weeks of age and fed ad libitum during two consecutive 6-week periods. Live weights and feed intakes were determined weekly. Significant protein × fiber interaction for body gains, corrected for digestive fill, indicated that response to added protein depended on the amount of ration fiber. Protein intakes for maximum live weight gains for 11, 18 and 25% ADF were .47, .66 and .58 kg and produced gains of .97, .91 and .76 kg/day. Dry matter intake increased at all fiber percentages as protein increased from 9 to 14.5% and decreased as protein was further elevated in 11 and 25% ADF diets. Serum urea did not increase, when protein was raised from 9 to 11.5%, but increased sharply as ration protein was elevated above 11.5%. For a corrected body weight gain of .60 kg/day (corrected for digestive tract contents), protein requirements were 271, 318, and 407 g/day for 11, 18 and 25% ADF rations. Net energy gain requirements did not change with varying protein and were determined as .52, .96, 1.32 and 1.61 Mcal/day for corrected body weight gains of .2, .4, .6 and .8 kg/day for the 100 kg live weight calf. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.