Ovarian fertility reserve, present in form of primordial follicles,  which represent the longevity and quality of reproductive activity. Complete depletion of fertility reserve with age due to high rate of consumption will lead to the cessation of ovarian function in mammals and specifically menopause in women. The initial transition from primordial to primary follicle is the key limiting step of follicle development and consumption. Folliculogenesis is primarily a gonadotropin-dependent process in addition to the role of several other factors such as the bone morphogenetic proteins (BMPs). However, the regulation of initial follicle development is generally known as gonadotropin-independent but other conflicting reports indicate otherwise and this discrepancy needs to be unequivocally clarified. Using a computerised stereological analysis the aim of this study was to investigate the role of BMPs in the regulation of primordial follicle depletion and rate of primary follicle survival in different ages of passively immunized mice against BMP receptor 1B (BMPR1B) and BMP-4 with and without treatment with the gonadotropin PMSG. The mean total numbers of primordial follicles in immunized mice with anti-BMPR1B and anti-BMP-4 were significantly (p<0.0001) increased with ratios up to 205% to the numbers present in control animals of the same age. Treatment with PMSG alone has no effect on the numbers of primordial follicles. However, PMSG treatment of immunized mice abolished the increase in numbers of primordial follicles resulted from immunization. The mean total numbers of primary follicles in immunized mice were also significantly (p<0.0001) increased with ratios up to 175% to those present in control animals of the same age. In contrast to the case of primordial follicles, treatment with PMSG alone or as a supplement with antibodies significantly reduced the number of primary follicles to a minimum ratio of 59% of follicles in control animals. The rates of primary follicle survival were decreased after puberty with age and particularly significant in treated animals. However, there was no significant difference in the survival rates of primary follicles between the different treatment groups within a given age.