Nitrogen retention in the pig.

I. 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 divided by N intake) was essentially independent of W, whereas the gross efficiency of N utilization (NR divided by N intake) was influenced by both W and N intake.