The effect of dietary crude protein level on intake, growth, protein retention and utilization of growing male Saanen kids

The effects of increasing dietary levels of crude protein on growth, feed i ntake, feed efficiency and composition of gain in male Saanen kids: were st udied. Four groups of four kids each initially weighing 12.1 +/- 0.18 kg an d having a weight gain of 195 +/- 16 g/d were penned individually and fed f or 73 to 124 days up to 25 kE of BW. They were fed chaffed wheat straw (45 g CP/kg DM) which had been molasses sprayed (10%) and pelleted concentrates containing 8.7, 11.7, 14.3 and 17.6% crude protein (CP) on DM basis, the r atio of straw to concentrate bring 1:5. Kids were fed controlled to satiati on in which case small amounts of the feeds were offered about five times a day as long as the kids wanted to eat. Retention of protein, fat and energ y were calculated from their initial and final concentrations in the empty body homogenates of the slaughtered kids. With increasing CP level in the d iet, feed intake increased from 448 to 608 g DM/d, weight gain from 94 to 1 81 g/d, retention of protein from 9.7 to 27.8 g/d, retention of fat from 9. 6 to 19.1 gld and feed efficiency improved from 4.79 to 3.39 kg DM/kg weigh t gain. Protein composition of gain increased from 103 to 154 g/kg BWG whil e fat (103-105 g/kg BWG) remained constant. Regression analyses showed that BWG can be optimized at 136 g CP/kg DM and protein retention at 180 g CP/k g DM, whereas, dietary nitrogen was utilized most efficiently at 120 g CP/k g DM. Extrapolated from the regression equations, maintenance N requirement of the kids at zero N-retention and at zero BWG were 0.38 and 0.16 g N/kg W-0.75, respectively. Recommended dietary CP concentrations and maintenance N requirements depend on the traits desired. (C) 2001 Elsevier Science B.V . All rights reserved.