934 HUMAN MILK: COMPARISON OF NITROGEN (N) COMPOSITION IN MILK FROM MOTHERS GIVING BIRTH PREMATURELY OR AT TERM

Complete 24-hour expressions of human breast milk were collected serially from 7 mothers giving birth at 26-33 wk gestation (Premature,PT) and 8 mothers at 38-40 wk gestation (Full-term,FT) during the first 29 days postpartum. Individual milk samples (69) were analyzed for total N concentration. The regression lines describing the change in N concentration (y) with time in days (d) were y=368 - 4.36d (r=-0.60,p<0.01), and y=310 - 4.15d (r=-0.80,p<0.01), for PT and FT, respectively. Total N concentration in PT milk was significantly higher (p<0.01) than in FT milk over the time studied. The distribution of total N in non-protein N (NPN) and protein N was determined on 7 PT and 8 FT pooled milk samples, representing specific day intervals within each group. NPN as a percent of total N remained constant over the first 29 days of lactation and was similar in the two groups (FT=18.9±0.7,PT=17.8±0.8, mean ± SEM). The proportions of N derived from free amino acid N (FAAN) and urea N(UN) were constant with time and as a percentage of NPN were similar in the FT(7.9±0.4 FAAN;26.8±1.7UN) and PT (8.4±0.7FAAN;25.8±2.0 UN) groups. It is concluded that the higher N concentration of PT milk is due to proportional increments in both the protein and NPN fractions.