Heat detection is one of the most important skills a pig farmer must develop. Missing the heat period means missing the chance to mate the sow, which results in a loss of 21 days (one full cycle). According to ICAR, poor heat detection is a major cause of low conception rates and longer farrowing intervals in India . A farmer should check sows for heat signs twice daily — morning and evening.

Signs of Heat (Estrus) in Sows

The following signs indicate that a sow or gilt is in heat:

• Swollen, red, and moist vulva (most visible sign)

• Restlessness — the sow walks along the fence, appears uneasy

• Loss of appetite — she may eat less than usual

• Mounting other pigs or standing still when other sows mount her

• Frequent urination with a strong smell

• Pricking of ears when touched on the back

• Discharge of clear mucus from vulva

• The sow seeks out and follows the boar

The Boar Exposure Method (Most Reliable Method)

The most reliable and ICAR-recommended method of heat detection is the boar exposure method. In this method, a mature boar (at least 12 months old) is walked along the sow pens or placed adjacent to sows for 10–15 minutes every morning and evening. The smell, sound, and presence of the boar stimulates the sow to show her heat signs clearly. This method is especially helpful in cases where silent heat is common.

Back Pressure Test (Standing Reflex Test)

This is a simple field test. The farmer applies firm pressure on the sow's back with both hands while standing behind her. If the sow stands still and does not move (lordosis response), she is in heat and ready for mating. If she walks away, she is not in heat. This test is most reliable when performed in the presence of a boar.