Detecting oestrus in breeding pigs

Identification of oestrus needs to be carried out each day. A sow is in oestrus ('heat') for 50–60 hours and will mate during that time, but she is only very fertile for 24–32 hours.

Signs of oestrus


The period before oestrus proper lasts 2–4 days. The signs of approaching oestrus include:

  • the sow mounting others when she is in a group
  • swelling and reddening of the vulva (there is little mucous secreted from the vagina at this stage)
  • sows honking, losing their appetite and appearing nervous and restless
  • the sow looking for the boar.


The signs of the onset (beginning) of oestrus include:

  • the sow accepts the boar's sexual advances (i.e. 'stands' or stands still)
  • the vulva is still red and swollen and watery mucous is seen often after sexual stimulation
  • the ability of only the boar to get the sow to stand and insemination (at this time) results in poor fertility.

Peak fertility

  • Occurs in the middle of 24 hours of oestrus (i.e. it starts about 12 hours after the onset of oestrus)
  • Boar and trained staff member can get a strong standing reaction (standing heat) during this time
  • Swollen, red vulva has noticeably subsided
  • Plenty of mucous and it has better lubricating qualities than the mucous that is produced at the beginning of oestrus
  • Mucous colour changes from clear to greyish at peak fertility
  • Sow stands for the boar in the last 12–24 hours but is less inclined to do this for the handler
  • Insemination in the last 12–24 hours gives poor results.

Identifying oestrus by the presence of a boar

Oestrus in a sow may also be detected by the presence of a boar:

  • introduce the boar and allow nose-to-nose contact with the sow
  • allow the boar to attempt to mount the sow (this could take up to 2 minutes).

The boar should be removed if the sow does not stand or if she attempts to bite or fight the boar. Also, separate the sow and the boar if oestrus detection is for the purpose of using AI.