Symposium on Growth: Physio-Genetics of Prenatal and Postnatal Growth

Abstract

The neonate is a result of a series of orderly processes that transform a single-celled ovum into an organism typical of the species. During the early cleavage of the fertilized ovum; cell size decreases progressively with little change in shape; the organism is approximately spherical. During the growth of the embryo, there is an increase in cell number with no change in cell size; the major tissues, organs and their major systems are differentiated. During the fetal stage, the various organs of the fetus grow at vastly different rates, resulting in continuous changes in the conformation of the organism. During the first week after fertilization, sheep and cattle embryos develop at the same rate (Green and Winters, 1945). Then a divergence in the rate of development is noted. Maximum growth in the prenatal life takes place after the formation of the extra-embryonic membranes, differentiation of tissues and organo-genesis. Absolute prenatal growth continues throughout gestation while relative growth (percentage increment change) begins to decrease about midway in gestation. Copyright © 1963. American Society of Animal Science . Copyright 1963 by American Society of Animal Science