Synchronisation of ovulation for management of reproduction in dairy cows.

Important developments have occurred in the last two decades, since the advent of the Ovsynch protocol, on the understanding and use of synchronisation programmes for management of reproduction in dairy herds. This better understanding of oestrus cycle control associated with suboptimal reproductive performance in dairy herds has led dairy producers to quickly adopt timed artificial insemination (AI) protocols. Recent surveys have documented that fixed-time AI has become an important component of management of reproduction in high-producing herds. Furthermore, timed AI protocols have also demonstrated benefits in pasture-based milk production systems because of the ability to increase insemination rate. In general, successful use of the Ovsynch protocol requires some fundamental physiological principles to be respected, including: induction of ovulation to synchronise follicle growth in the first 2 days of the programme such that a young antral follicle is recruited; maintenance of high concentrations of progesterone during the development of the ovulatory follicle, but also effectively lyse the corpus luteum to result in very low concentration of progesterone at AI; and having a healthy pre-ovulatory follicle of moderate diameter that is highly oestrogenic and responsive to gonadotropins to synchronously ovulate 12 to 18 h after insemination. Current methods oestrous and ovulation synchronisation are still not optimal and future improvements will likely require new technologies for hormone formulation and delivery such that additional interventions are minimised to maintain acceptance by producers.