Swine Gestation Calculator

A swine gestation calculator estimates the expected farrowing date (EFD) for a sow or gilt from the known breeding (service) date. The practical rule is “three months, three weeks, and three days,” or about 114 days, but any seasoned producer knows there is natural variation. Accurate projections let you schedule farrowing crates, adjust feed and body condition targets, order supplies, and plan staff coverage without guesswork. This guide explains how such a calculator works, what the results mean, and how to use those dates to drive better herd management.

What the Calculator Does

A typical tool accepts one or more service dates and returns:

• Expected Farrowing Date (EFD): Breeding date + 114 days.
• Farrowing Window: A practical range, usually 112–115 days, to reflect normal biological spread.
• Pre‑Farrowing Checklist Timing: Suggested due dates for vaccinations, deworming, crate moves, and wash‑in.
• Feed Curve Reminders: Staging points to maintain ideal body condition without over‑ or under‑feeding.

How to Use the Dates in Practice

1. Record the service date as soon as breeding occurs—precision matters.
2. Enter the date(s) into the calculator to generate the EFD and the 112–115 day window.
3. Layer on management tasks (moving to farrowing, vaccinations, deworming, teat/udder checks, and sanitation).
4. Check barn capacity and schedule crates, heat‑lamps, mats, and supplies accordingly.
5. Share the calendar with staff so everyone is synchronized on critical days.

The Math Behind the Projection

The core calculation is straightforward:

EFD = Service Date + 114 days

Because individual sows, parity, season, stress, and health can shift the outcome, good calculators also show a range. A practical on‑farm convention is:

Farrowing Window = [Service Date + 112, Service Date + 115]

Some herds see slightly different patterns (e.g., 113–116). Track your own data and tune the window to reflect herd‑specific reality.

Interpreting the Output

Field	What It Means	How to Use It
Expected Farrowing Date (EFD)	The single most likely date based on 114‑day gestation.	Use for staffing rosters, feed staging, and readiness checks.
Farrowing Window	Normal statistical spread (commonly 112–115 days).	Have crates, colostrum supplements, and heat sources ready for the whole window.
Trimester Flags	Markers for early, mid, and late gestation phases.	Match feed curves and body condition scoring to each phase.
Pre‑Farrowing Tasks	Auto‑calculated target days for vaccines, deworming, and moves.	Arrive clean, dry, and calm in the farrowing room to reduce stillbirth risk.

Management Timeline Anchored to Gestation Day

Aligning herd actions to gestation day keeps the right things happening at the right time. The table below summarizes common milestones and management focus areas.

Gestation Day	Milestone	Management Focus
0–1	Service (breeding)	Record sire, sow ID, parity, and exact date/time. Minimize stress.
18–24	Return‑to‑estrus window	Observe for returns; re‑breed if needed. Good records improve accuracy.
28–35	Pregnancy check	Ultrasound or other diagnostics. Update records to confirm the gestation clock.
40–70	Organ development	Steady nutrition; avoid over‑conditioning in gilts. Maintain parasite control.
70–95	Rapid fetal growth	Review body condition and adjust feed. Ensure comfortable temperature and airflow.
90–100	Pre‑farrowing vaccinations (herd‑specific)	Boost colostral antibodies. Confirm with veterinarian and your herd protocol.
~110	Move to farrowing room	Wash and dry, calmly load into clean, warm crates. Prepare heat‑lamps and mats.
112–115	Farrowing window	24/7 observation, colostrum management, navel dipping, teat checks, cross‑fostering plan.

Feed Curves and Body Condition

The goal is to farrow sows in correct body condition—neither thin nor over‑fat. The calculator’s schedule helps you time reviews and adjustments. Example planning guide:

Phase	Typical Days	Target Intake (kg/day)	Notes
Early	0–35	2.0–2.2	Emphasize consistent intake; avoid abrupt diet changes.
Mid	36–80	2.2–2.5	Adjust for parity and BCS. Maintain mineral balance and clean water.
Late	81–114	2.5–3.0	Support fetal growth; monitor for constipation; confirm laxative fiber if needed.

Values are examples only. Use your nutritionist’s recommendations and feed label specifications for your herd and genetics.

Pre‑Farrowing Checklist and Timing

Use the farrowing window to backward‑plan final tasks. Here is a compact checklist you can adapt:

Timing Relative to EFD	Task	Why It Matters
EFD – 21 to –14 days	Vaccinations per herd protocol	Maximize colostral antibodies for piglet disease protection.
EFD – 14 to –10 days	Deworming if indicated	Reduce parasite load before farrowing and lactation.
EFD – 7 days	Finalize crate assignments, heat sources, and supplies	Avoid last‑minute scrambling—everything ready for 112–115.
EFD – 4 to –2 days	Move to farrowing house (often around day ~110)	Allow settling in; reduce stress that could disrupt farrowing.
EFD – 1 day	Final checks: temperature, waterers, disinfected tools	Eliminate environmental surprises for sow and staff.

Barn Scheduling and Capacity Planning

Calculator outputs are most powerful when rolled up across the herd. Group EFDs to visualize weekly farrowing loads and prevent bottlenecks. Consider:

• Crate Count: Ensure enough farrowing spaces for the whole 112–115 window, not just the EFD.
• Heat Management: Piglets need warm zones; mothers need comfort without overheating.
• Labor Roster: Align shifts to the predicted high‑activity nights. Cross‑train staff for colostrum and fostering.
• Supply Chain: Order disinfectants, iodine, gloves, syringes, and supplements in advance.
• Weaning Flow: Remember that farrowing schedules drive weaning dates and nursery occupancy.

Record‑Keeping for Better Predictions

The more consistent your records, the better the calculator performs over time. Capture:

• Exact service date and time; boar or semen ID; parity and sow ID.
• Heat/return observations between days 18–24 and 39–45.
• Pregnancy confirmation date and method.
• Body condition changes and feed adjustments by phase.
• Actual farrowing date and number born alive/stillborn to refine herd‑specific windows.

Why Gestation Length Varies

Biology is precise and variable at the same time. Genetics, parity (gilt vs. sow), litter size, stress, season, nutrition, and health status can nudge farrowing earlier or later than the 114‑day average. That’s why planning around a window is superior to planning around a single date. Your own historical data can reveal, for example, that parity‑1 females tend to farrow a little later, or that extreme heat nudges farrowing earlier in your barns. Use these insights to tune decisions—without abandoning the convenience of the calculator.

Troubleshooting Common Scenarios

No Farrowing by Day 116

Re‑check records for the correct service date, confirm pregnancy status, and consult your veterinarian if clinical signs are atypical. Data entry mistakes are common; always verify IDs and dates first.

Apparent Early Farrowing

Confirm the service date, and consider environmental stressors (transport, thermal stress) or health issues. Review vaccination and parasite protocols and the move‑to‑crate process for sources of stress.

Returns to Heat After “Confirmation”

Early embryonic loss can mimic false positives. Tighten pregnancy check windows and standardize diagnostic methods. Log anything that could interfere with accurate readings.

Putting It All Together

A swine gestation calculator transforms a single breeding date into a comprehensive plan. By pairing the 114‑day EFD with a 112–115‑day window, you can create dependable schedules for farrowing spaces, feed, vaccinations, labor, and supplies. Track actual outcomes, compare them to predictions, and refine your herd’s window and protocols. The result is lower risk, smoother barn flow, and better piglet vitality.

This document is an educational guide. Always align with your herd veterinarian and nutritionist, and follow local regulations and welfare standards.