Reproduction

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

Q: How long after weaning does a sow come into heat?

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

Q: How long is a pig pregnant?

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

Updated 1 Nov 20263 sources

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].

Related tools and references

More reproductive physiology

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References

Features of the Reproductive Cycle (table)MSD Veterinary Manual
Approximate Gestation Periods (table)MSD Veterinary Manual
Breeding Management of PigsMerck Veterinary Manual

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