Nitrogen retention in the pig

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Abstract
1. Published results have been used to study the relationships between nitrogen retention (NR), body-weight (W) and N intake in the pig.2. The general decrease in maximal NR (g/d per kg W0.75) with increasing W (kg) was curvilinear for values of W from 1.5 to 45: NR = 3.324−0.098 W+0.001 W2; and rectilinear for values of W from 45 to 165: NR = 1.252−0.006 W. Values for protein requirements derived from these equations agreed closely with published estimates.3. The slopes of the curves for NR (g/d per kg W0.75) v. N intake (g/d) decreased as W (kg) increased from about 2.5 to 190. After extrapolation to a proposed common intercept on the NR axis of -150 mg N/d per kg W0.75, regression analysis of the intercepts of these curves on the N-intake axis v. W gave an estimate of N requirements for maintenance of 246±19 mg/d per kg W0.75.4. The results also indicated that at low N intakes net protein utilization (N retention+ total obligatory N losses ÷ N intake) was essentially independent of W, whereas the gross efficiency of N utilization (NR ÷ N intake) was influenced by both W and N intake.