Similar to our observation, maternal leptin treatment or high
maternal plasma leptin concentration is often associated with
retarded fetal growth and lower birth weight in mammals. Pregnant
rats treated with human recombinant leptin give birth to lean
offspring with reduced skeletal growth (Nilsson et al., 2003). Feeding
pregnant ewes (Bispham et al., 2003) with high-protein diet
significantly increased materal plasma leptin concentration which
was accompanied by decreased fetal weight. However, injection of
recombinant mice leptin into the albumen of eggs on d 5 of incubation
advanced hatching, increased hatch weight and improved growth rate
during 56 days posthatching in quails (Lamosova et al., 2003). Our
results seem to contradict with that on quails concerning hatch
weight, but agree well on the fast growth rate during early posthatch
period. Multiple factors, including species, dose of leptin, timing of the
injection, etc., may contribute to the divergence of the results. It is
noted that leptin was administered into the eggs on day 5 of
incubation in quails (Lamosova et al., 2003), which differs from the
present study in which leptin was injected into fertile eggs before
incubation to better mimic the situation of natural deposition of
maternal hormones in the egg. In rodents, obstruction of prenatal
development was followed with the postnatal catch-up growth