Oestrus cycle of pig is

Oestrus cycle of pig is 21 days.
The oestrous cycle in pigs spans 18 - 21 days. It consists of a follicular phase of 5 - 7 days and a luteal phase of 13 - 15 days. During the follicular phase, small antral follicles develop into large, pre-ovulatory follicles.
The female pig (sow) is ready to breed (reaches puberty) at 5 months of age and will show signs of being in heat. Some slow growing types and animals which are underfed will be older when they reach puberty. The sow will come into heat every 3 weeks throughout the year if she is not mated.