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 intake, feed efficiency and composition of gain in male Saanen kids were studied. Four groups of four kids each initially weighing 12.1+/-0.18kg and having a weight gain of 195+/-16g/d were penned individually and fed for 73 to 124 days up to 25kg of BW. They were fed chaffed wheat straw (45g CP/kg DM) which had been molasses sprayed (10%) and pelleted concentrates containing 8.7, 11.7, 14.4 and 17.6% crude protein (CP) on DM basis, the ratio of straw to concentrate being 1:5. Kids were fed controlled to satiation 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 energy were calculated from their initial and final concentrations in the empty body homogenates of the slaughtered kids. With increasing CP level in the diet, feed intake increased from 448 to 608g DM/d, weight gain from 94 to 181g/d, retention of protein from 9.7 to 27.8g/d, retention of fat from 9.6 to 19.1g/d and feed efficiency improved from 4.79 to 3.39kg DM/kg weight gain. Protein composition of gain increased from 103 to 154g/kg BWG while fat (103-105g/kg BWG) remained constant. Regression analyses showed that BWG can be optimized at 136g CP/kg DM and protein retention at 180g CP/kg DM, whereas, dietary nitrogen was utilized most efficiently at 120g CP/kg DM. Extrapolated from the regression equations, maintenance N requirement of the kids at zero N-retention and at zero BWG were 0.38 and 0.16g N/kg W(0.75), respectively. Recommended dietary CP concentrations and maintenance N requirements depend on the traits desired.