Oestrus comes from a Greek word meaning 'mad desire'. As biologyonline.com points out, oestrus is a phase in the sexual cycle of female animals. It is characterised by sexual receptiveness in females. Other cues include a bloody vaginal discharge.
When the ovarian follicles mature, oestrogen is secreted. Females are said to be in heat during this phase. Anoestrus is that period when the sexual cycle rests.
Simply put, oestrus makes reproduction possible. If the breeding herd does not reproduce well, fewer pigs will be available to send to market.
When oestrus approaches, there).