Development and Senescence of the Postnatal Bovine Ovary

Abstract

Ovaries from 116 cows were excised and serially sectioned to permit histological and cytological analyses of the germ cells and their attendant follicles at varying periods from birth to 20 years of age. The population of females sampled was characterized by extreme individual variation in germ cell numbers, ranging from zero or sterility to 700,000 germ cells. Numbers of primordial follicles for a given individual apparently remain stable (133,000 average) until about the fourth year of life and decline thereafter until the near zero point is reached in ovaries from cows 15 to 20 years of age. Numbers of growing follicles rise rapidly between 50 and 80 days postpartum, increase gradually up to 120 days and decline concomitantly with the decline in primordial follicles at the fourth year. Vesicular follicles increase in number coincidentally with growing follicles with a lifetime high of 63 follicles at 180 days postnatal. A slight decline occurred at 8 months of age or near the time of puberty, and no further reduction was noted until the 10- to 14-year period. Primordial follicle quality remains high until 240 days postpartum, after which time most are in varying states of atresia. In most cases the vesicular follicle population is equally divided between the normal and atretic states. Normal follicles are generally in the majority in ovaries from cows up to 10 years of age, and atretic follicles predominate in later years. The significance of the wide individual variability in germ cell endowment is discussed.