The control of ovarian function in cattle involves the complex interaction of local and systemic feedback mechanisms. This control system ensures that in greater than 96% of cows only one follicle will ovulate each oestrous cycle. A better understanding of the mechanisms involved should lead to improved synchronisation of oestrus in herds, thereby increasing the success rate of artificial insemination, improve the effectiveness of superovulation regimes and provide opportunities for the induction of twinning. It has been estimated that modest improvements in these areas would benefit the UK cattle industry by at least £200 million per year.

Follicular growth in cattle occurs in a wave-like pattern with usually three waves, sometimes two waves but rarely four waves, of follicles growing and regressing each oestrous cycle. This follicle wave pattern is also present during periods of anoestrus. Each follicle wave, which is usually preceeded by a rise in peripheral FSH concentrations, is characterized by the emergence, from the pool of growing follicles, of a large ‘dominant’ follicle.