Female pigs, known as sows, typically reach puberty between five and twelve months of age. Once mature, they experience estrus cycles approximately every 21 days, though this can range from 18 to 24 days depending on the individual.
The actual period of heat, or estrus, usually lasts between two and four days. Because sows are polyestrous, they can go through multiple cycles throughout the year, making them capable of breeding fairly regularly under the right conditions.