Calculate expected farrowing dates for pregnant sows and gilts. Track pregnancy progress using the "3-3-3 rule" for accurate breeding management.
Last updated: March 2026
Swine gestation is the period from breeding to farrowing (birth) in pigs, lasting 111 to 120 days with an average of 114 days. Pig farmers commonly remember this as the "3-3-3 rule": 3 months, 3 weeks, and 3 days.
This remarkably consistent gestation period allows for precise breeding schedules and farrowing management. Unlike many livestock species, sow gestation length varies minimally between breeds and parity (number of previous pregnancies), making planning straightforward and reliable.
Understanding gestation timing is essential for maximizing farrowing success. Proper nutrition, housing transitions, vaccination schedules, and farrowing preparation all depend on accurate gestation tracking. Commercial operations often synchronize breeding to create farrowing groups, allowing efficient use of facilities and labor.
The calculator uses standard swine gestation ranges:
Key pregnancy milestones for sow management:
The easiest way to remember swine gestation: 3 months + 3 weeks + 3 days = 114 days
This simple formula helps farmers quickly calculate farrowing dates without a calculator.
A sow was bred on January 1, 2026:
Very reliable! Swine gestation is one of the most consistent in livestock. About 90% of sows farrow within 2 days of day 114. The 3-3-3 rule (3 months, 3 weeks, 3 days) is an easy memory aid that producers have used successfully for generations.
Gestation length is nearly identical for gilts (first-time mothers) and sows (experienced mothers), both averaging 114 days. However, gilts may need extra monitoring as they're more likely to have smaller litters and may require assistance during farrowing.
Move sows into farrowing crates or pens 3-7 days before expected farrowing (around day 107-111). This gives them time to acclimate to the new environment and reduces stress during the critical farrowing period.
Signs include restlessness, nest-building behavior, udder development and milk letdown, vulva swelling, refusal to eat (12-24 hours before), and rectal temperature drop. Most sows farrow within 24 hours of refusing feed.
Modern commercial sows average 12-14 live births per litter, though this varies by genetics and parity. Gilts typically have smaller litters (8-10 piglets), while mature sows (parities 3-5) have the largest litters. Litter size has increased significantly through genetic selection.
Yes. Feed a gestation diet (lower energy) for days 0-90 to prevent sows from getting too fat. Around day 90-95, transition to a lactation diet (higher energy and protein) to support rapid fetal growth and prepare for milk production.
Pregnancy can be confirmed by ultrasound (28-35 days post-breeding), lack of return to estrus (18-24 days post-breeding), or visual signs like abdominal enlargement (50+ days). Ultrasound is most accurate and allows early detection of non-pregnant sows for re-breeding.
If no farrowing by day 120-121, verify the breeding date. If confirmed accurate, consult a veterinarian as intervention may be needed. Delayed farrowing can indicate problems like uterine inertia, oversized piglets, or incorrect breeding dates.
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