Fig. 1

Reproductive hormone profile during the porcine oestrous cycle and the corresponding stages of folliculogenesis. Profile of luteinising hormone (LH, red), follicle stimulating hormone (FSH, blue), oestradiol (E2, purple) and progesterone (P4, green) during the oestrous cycle of the pig and the corresponding stages of folliculogenesis. The initiation of the primordial follicle (a) to a secondary follicle (b) is induced by the increase in FSH which is followed by the expansion of the secondary follicle to the tertiary (antral) follicle (c) and then eventually to the pre-ovulatory follicle (d). This is accompanied by the increase in P4 which is involved in preparing the endometrial lining, and the increase in E2 which initiates the rapid release of LH. This LH surge results in the rupture of the follicle, an event known as ovulation (e). The relative hormone levels show the within hormone changes during the cycle; E2 concentrations are in pg/mL whilst P4, FSH and LH are in ng/mL