# Pig Reproduction: Estrus, Ovulation, Insemination Timing, Farrowing & Litter Size

> Reproductive physiology of the sow and gilt: 21-day cycle, estrus 36–48 h in gilts and ≥ 48–72 h in sows, ovulation about 70% through estrus, insemination timing, estrus 3–7 days after weaning, gestation 114–116 days.

- Source page: https://wevet.in/reproduction/pig/
- Type: Reproduction
- Publisher: WeVet
- Updated: 2026-11-01
- Audience: veterinarians and veterinary students

Key reproductive figures for pigs from the MSD Veterinary Manual reproductive-cycle and gestation tables [1][2] and the Merck Veterinary Manual chapter on breeding management of pigs [3].

## Key figures

| Feature | Pig | Source |
|---|---|---|
| Age at puberty | 6–7 months | [1] |
| Cycle | Polyestrous all year; 21 days (19–23) | [1] |
| Duration of estrus | 36–48 h (1–2 days) in gilts; ≥ 48–72 h (2–3 days) in sows | [3] |
| Ovulation | Generally around 70% of the way through estrus; approx. 15–24 ova released over a 1- to 4-hour period | [3] |
| Gestation | Ranges 115–116 ± 1 days from first service (average has been increasing) | [3] |

## Detecting estrus and timing insemination

- The ultimate criterion of estrus is standing to the boar or a positive response to the back-pressure test [3].
- Behavioural signs of estrus are most pronounced when the sow or gilt is intermittently exposed to a mature boar [3].
- With heat checks twice a day, gilts and sows should be inseminated 8–12 hours after the onset of standing heat and again 12–16 hours later; with once-daily checks, within 0–4 hours of detection and again 24 hours later [3].
- Most sows show estrus 3–7 days after weaning [3].

## Litter and farrowing

- Embryonic loss of 30–40% is common, which accounts for the usual litter size of 12–16 total born pigs [3].
- The stillbirth rate is usually 5–10% [3].
- Piglets are usually delivered at frequent intervals — on average every 10–15 minutes (range 5–45 minutes) [3].
- Farrowing fewer than five piglets can indicate breeding failure or early embryonic death [3].

## How the sources compare

| Feature | MSD reproductive-cycle and gestation tables [1][2] | Merck breeding-management chapter [3] |
|---|---|---|
| Duration of estrus | 40–60 h | 36–48 h in gilts; ≥ 48–72 h in sows |
| Ovulation | Approx. 40 h after the onset of estrus | Around 70% of the way through estrus |
| First estrus after weaning | 4–10 days | Most sows 3–7 days |
| Gestation | 114 days | 115–116 ± 1 days from first service |

## Frequently asked questions

### When should a sow be inseminated?

With twice-daily heat checks, 8–12 hours after the onset of standing heat and again 12–16 hours later; with once-daily checks, within 0–4 hours of detection and again 24 hours later [3].

### How long after weaning does a sow come into heat?

Most sows show estrus 3–7 days after weaning [3]; the MSD reproductive-cycle table gives 4–10 days [1].

### How long is a pig pregnant?

The MSD gestation table gives 114 days [2]; the Merck breeding-management chapter states that the average has been increasing and now ranges 115–116 ± 1 days from first service [3].

## References

[1] Features of the Reproductive Cycle (table) — MSD Veterinary Manual. https://www.msdvetmanual.com/multimedia/table/features-of-the-reproductive-cycle
[2] Approximate Gestation Periods (table) — MSD Veterinary Manual. https://www.msdvetmanual.com/multimedia/table/approximate-gestation-periods
[3] Breeding Management of Pigs — Merck Veterinary Manual. https://www.merckvetmanual.com/management-and-nutrition/management-of-reproduction-pigs/breeding-management-of-pigs

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Numbers in [brackets] cite the references above. For veterinary professionals. Information supports — never replaces — clinical judgement; always check the current product label and local regulations.
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