Reproductive function in prepubertal lambs: ovulation, embryo development and ovarian steroidogenesis

Area of Science:

• Reproductive biology
• Endocrinology
• Animal science

Background:

• The reproductive capacity of immature animals is a key area in livestock management.
• Understanding ovarian function in young sheep can inform breeding strategies.

Purpose of the Study:

• To investigate the effects of pregnant mare serum gonadotropin (PMSG) and progesterone pretreatment on ovulation and ovarian function in immature Welsh Mountain lambs.
• To assess the developmental potential of oocytes from PMSG-treated lambs.

Main Methods:

• 23 lambs were treated with PMSG, with varying durations of progesterone pretreatment.
• Ovulation rates were recorded, and oocytes were tested for fertilization and development in rabbits and by embryo transfer to adult ewes.
• In vitro steroid secretion from ovarian follicles was analyzed.

Main Results:

• Ovulation rate increased with longer progesterone pretreatment durations.
• Human chorionic gonadotropin (HCG) did not affect ovulation.
• Fertilized oocytes developed to the morula stage and resulted in a live lamb after transfer.
• Luteal function was comparable to nonpregnant ewes, with elevated progesterone levels in specific conditions.
• Lamb ovarian follicles showed similar steroidogenic capacity to adult ewes, with higher initial estrogen production and decreased testosterone production after progesterone pretreatment.

Conclusions:

• Immature lamb ovaries can be stimulated to ovulate and produce viable oocytes following PMSG treatment and appropriate progesterone pretreatment.
• The endocrine and developmental competence of oocytes from PMSG-primed lambs is comparable to that of adult ewes.
• These findings suggest potential for manipulating reproductive cycles in young sheep.