Estrous Cycle in the Sow (Female Pig)

The average length of the estrous cycle in the sow (female pig) is 21 days and may vary from 18-23 days.

The sow is a polyestrous species, meaning she exhibits multiple estrous cycles throughout the year without being restricted to specific breeding seasons.

• The estrogenic phase of the cycle is 6-7 days.
• The luteal phase is 14 days with corpus luteum regression beginning on day 16.
• The duration of estrum is 1-4 days, with an average of 2-3 days.
• Silent heats occur in about 2% of porcine cycles.
• Senility (after 6-10 years) may affect estrous cycle.

Symptoms of Estrus (Heat) in Pig

Estrus or heat symptoms are definite and marked and include:

• Reduced appetite
• Restless and nervous
• Often pace back and forth by the fence
• Salivation
• Champing of the jaws
• Sow, if suckling, may ignore her piglets, may try to escape or if free will seek out the boar and stand for service
• Vulval lips swollen and congested
• Mucous membrane pinkish-red
• Mucous discharge
• Mounting other animals
• Grunting and standing motionless for long periods in a position for service is the most noticeable feature. This peculiar immobilizing reflex or stance (lordosis response) can be produced by applying pressure of the hands on the sow’s back or by straddling the sow.