Maturation of Bovine Female Genitalia from Birth through Puberty

Abstract

Sixty-five Holstein heifers were killed at monthly age intervals in groups of five from birth through 12 mo. of age to determine morphological and biochemical criteria of their reproductive organs. Ovarian weight increased 2.7 times faster than bodyweight. While no ovarian follicles were visible macroscopically at birth, their numbers increased to a maximum at 4 mo., decreased to 8 mo. of age and remained relatively constant thereafter. Gross anatomical and biochemical criteria of uteri, cervices and vaginae increased at rates similar to rate of body growth until 6 mo. of age, but shifted to more rapid growth thereafter. These changes in rates of reproductive growth were most pronounced for organ weights, RNA content and protein content and less marked for DNA content. Height of the luminal epithelium of the tubular genitalia was stimulated at birth and regressed by 1 or 2 mo. of age. Thereafter, increases in height of epithelia in vaginae, cervices and uteri were most rapid after 6 mo., similar to changes in organ weights. Further, secretion blebs on oviducal and cervical epithelia and bodies similar to nuclei apparently extruded from oviducal epithelial cells became more abundant after 6 mo. of age. These data indicate that rapid puberal growth in Holstein heifers commences during the seventh month of age and is largely terminated by 10 mo. because several of the measured criteria increased at reduced rates after this age.