EFFECT OF SUPEROVULATION WITH PFSH OR PMSG ON GROWTH AND MATURATION OF THE OVULATORY FOLLICLES IN SHEEP

Morphological (growth rate, size, granulosa cell number) and functional (steroidogenesis, in vitro response to luteinizing hormone (LH) ) features of follicular growth and maturation were compared during untreated cycles or after superovulation induced by PMSG or pFSH. In vivo alterations in the pattern of follicular growth induced by PMSG administration were monitored by repeated ink marking of the largest follicles. PMSG increased ovulation rate by: (1) recruiting small follicles; (2) causing up to a threefold increase in follicular growth rate; (3) altering the size distribution of the largest follicles at oestrus but not by reversing atresia. Comparison of the morphological features of the preovulatory follicles of control and PMSG superovulated ewes demonstrated a mean smaller size, an increased spread of this size and of the granulosa cell content in PMSG treated compared with control follicles. Comparison at 16 h after sponge removal of large follicles of control, pFSH (15 mg) or PMSG (1000 IU) treated ewes showed that those of control and PMSG treated ewes had a similar granulosa cell complement, whereas pFSH treated follicles were deficient in granulosa cells. When steroid production of these follicles was examined, using in vitro incubation of intact follicles, PMSG treated follicles exhibited a higher progesterone production while pFSH treated follicles exhibited a decreased oestradiol production compared with control follicles. Furthermore, all follicles had retained their sensitivity to LH as evidenced by increased testosterone production after addition of LH to the incubation medium.