Background Preterm human milk has higher protein and electrolyte content versus term human milk during the first 2 wk postpartum and may reflect increased needs for growth by preterm infants. In our lab, a lamb model of prematurity with prolonged assisted ventilation for 21 d is used to study chronic lung disease. Provision of adequate nutrients is needed to minimize potential confounding effects of poor nutrition on outcome variables. Protein and zinc (Zn) are nutrients of particular interest because they play an essential role in metabolism and organ growth and development. The protein and Zn content of preterm ewe milk, however, is unknown.
Purpose To compare total protein and Zn content of preterm (PT) vs term (T) ewe milk, to test the hypothesis that preterm ewe milk has higher protein and Zn content.
Design Milk samples were obtained q 4 h and pooled at 24 h intervals from d 1-21 postpartum from healthy ewes delivered preterm (131-133 d gestation) by cesarean section (n = 6). Aliquots of daily pooled samples were analyzed. Fat content was determined from fresh samples by the crematocrit technique. The remaining samples were frozen at -70°C until analysis. Total protein (g/dL) and Zn (mg/dL) values were determined at d 1-7, d 10, d 14, and d 21 by colorimetric assay. PT to T ewe milk reference values were analyzed by t-test.
Results Mean total protein and Zn concentrations were greater in PT (() vs T (() ewe milk from d 1-21, with the largest differences observed from d 1-7 (p ≤ .05; Figures 1 and 2). Total fat content was lower in PT ewe milk on d 1 (3.1 ± 0.6 g/dL PT vs 5.6 ± 0.6 g/dL T, p = .001) but similar to T ewe milk thereafter (Figure 3).
Conclusion Premature delivery alters the nutrient composition of ewe milk, as evidenced by a two- to three-fold greater concentration of total protein and Zn during the first 21 d of lactation, similar to the differences between human PT vs T milk, presumably to meet needs for growth and development of the preterm lambs.
Supported by CHRC, HL62875, HL56401, T35 HL07744.