A red, swollen vulva on a pig means one of three things: heat, late pregnancy, or pathology. The answer hinges on three checks: where she is in her 21-day cycle, how long since she was bred, and whether the corn has been damp. About 8.2% of PH maize samples carry zearalenone, which causes the same swelling without heat or pregnancy.
The Quick Differential
| Cause | Vulva look | Discharge | Other signs | Timing |
|---|---|---|---|---|
| Heat (estrus) | Red, swollen | Clear → sticky mucus | Standing reflex, ear-stand, vocal | 21-day cycle; signs gone in 3 days |
| Late pregnancy | Swollen, elongated, deep pink | Clear; milk in teats 24-48h pre-farrow | Bagging up, nest-building, restless | ~114 days post-breed |
| Zearalenone | Swollen, reddened in piglets or non-cycling gilts | None or clear | Enlarged piglet teats; whole pen affected | Persists past 3 days; resolves only when feed changed |
| Endometritis | Mildly swollen | White/yellow/grey, foul, up to 90 mL | Failed breeding, returns to heat, sometimes off-feed | Post-service |
| Pyometra | Swollen | Pus, intermittent | Anestrus, dull, weight loss | Older sows |
| Cystitis (UTI) | Wet, soiled | Blood/pus in urine, frequent urination | Common first 21 days post-mating | Any time |
| AI/breeding trauma | Swollen, sometimes bruised | Slight blood, clears in 1-2 days | Recent service | Resolves in 72h |
| Vulva biting | Torn, bleeding | Fresh blood | Blood on pen-mates' noses | Group pens |
| Vaginal prolapse | Pink tissue protruding | None | Older, fat sow | Late pregnancy |
Normal: Heat, Pregnancy, Post-Farrow
Heat swelling starts 2-3 days before the standing reflex, during a pre-heat phase that Queensland's Department of Agriculture puts at about 2-4 days, and fades within 3 days of estrus passing. The peak is bright red and tense, the discharge moves from clear to sticky mucus, and a back-pressure test on a sow in standing heat will hold her still while another pig mounts. AI window: 12-24 hours after standing reflex first appears in sows; for gilts, breed at first standing and again 24 hours later. The full picture is in how to tell a sow in heat.
Late pregnancy swelling starts 10-14 days before farrowing, peaks in the last 3-5 days, and is paired with bagging up. The udder fills 48-72 hours before farrow, and milk can be expressed 24-48 hours before. Gestation runs about 114 days ("3 months, 3 weeks, 3 days"). Cross-check with how to tell a pig is pregnant and the difficult farrowing guide.
Post-farrowing, the vulva stays swollen with bloody-brown discharge (lochia) for 3-5 days. Should be clean and odourless by day 7. Foul or persistent discharge after a week is endometritis until proven otherwise.
Pathology: When It Is Not Heat And Not Pregnancy
Zearalenone (mouldy corn) — the PH lead suspect
The most under-diagnosed cause in Philippine backyard pens. A 2019 PH maize survey by Salvador et al. across 18 provinces found 8.2% of samples positive for zearalenone. Tropical humidity plus corn stored in sacks on concrete equals ideal Fusarium conditions. Pigs are the most sensitive species. As little as 1-5 ppm in feed triggers vulval swelling in pre-pubertal gilts and weaners.
Tell-tale signs: a whole pen of weaner gilts develops red swollen vulvas; piglets show enlarged teats; gilts are not cycling. Inspect the corn for clumping, dark spots, off-smell and dust around the bag. Switch to a clean batch immediately. Add a mycotoxin binder (Toxoff ₱350-500/L, or activated charcoal as a budget fallback) through the May-November humid months. See Philippine feed economics.
The Merck Veterinary Manual notes severe straining can cause vaginal or rectal prolapse, so a swollen weaner and a rectal prolapse in one pen are one problem. Merck adds that zearalenone passes into the sow's milk, so suckling piglets can swell too. Merck calls charcoal-type binders impractical at the doses needed, so dry corn is the real fix.
Recovery is slow: Merck says about 1 week after changing grain (up to 3); ThePigSite's mycotoxicosis guide says three to four weeks. A University of Southern Mindanao study found storage fungi grew more at 20-22% grain moisture than at 14-18%.
One trap: ThePigSite says 5-10 ppm can put sows into anoestrus with pseudo-pregnancy. A sow that never came back into heat is not proof she's pregnant.
Endometritis
A discharge of cloudy, foul-smelling pus after service, usually first seen 10-20 days after breeding (ThePigSite, Endometritis and Vulval Discharge). Volumes run highest in endometritis, around 90 mL, and in those cases the farrowing rate falls to about 14% (Food & Agribusiness, Vulval Discharge). The sow often returns to heat after a "successful" mating because conception failed. ThePigSite's guide advises culling problem sows, because treatment response is poor and such sows farrow only 50-60% of matings.
PH protocol: ceftiofur (Excenel RTU, ₱400-700 per 50mL) at 3-5 mg/kg IM once daily for 3 days. Or long-acting oxytetracycline (Terramycin LA, ₱350-500 per 100mL) at 20 mg/kg IM, repeated every 48-72 hours. Add oxytocin 10-20 IU IM to help uterine clearance. Cull persistent cases.
Cystitis and pyometra
Cystitis: blood-tinged urine, frequent urination, wet soiled vulva. Most PH cases trace to nipple-drinker failures or hot-pen dehydration. Fix water access first, then amoxicillin 15 mg/kg/day for 5 days.
Pyometra: pus discharge plus the sow refuses to come back to heat. Older sows. Usually a cull decision.
Vulva biting and prolapse
In group pens a swollen vulva gets bitten. The NADIS vulva biting guide says the more swollen it is, the likelier the bite, and that the first clue is usually blood on other sows' noses or the walls. Deep bites scar and can tear at farrowing, NADIS warns. Pen her alone and call the vet.
If the "swelling" is pink tissue pushing out between the lips, it's a vaginal prolapse. ThePigSite puts it at about one pregnancy in 200, mostly older sows (5th parity on) in late pregnancy, and warns a prolapse still out near farrowing can stop the cervix opening. Vet job.
Confirming Pregnancy
The vulva is a poor pregnancy test before the last two weeks. University of Illinois swine specialist Robert Knox describes a return-to-heat check three weeks after breeding; I back-pressure test days 18-24. He gives about 28 days for an ultrasound scan, retesting a week later if unsure. Ask your Municipal Agriculturist Office who scans sows locally, and log the date in the farrowing calculator.
A 6-Step Decision Tree
- Pre-pubertal piglet (1-6 months) swollen? Mycotoxin first. Check the feed before anything else.
- Adult sow with standing reflex + about 21 days since last cycle? Heat. Breed.
- About 110+ days since mating + bagging up? Late pregnancy. Set up the farrowing area.
- Foul discharge + off-feed + fever? Endometritis or pyometra. Vet.
- Persistent swelling more than 3 days with no heat and no pregnancy? Mycotoxin or pathology. Not normal cycle.
- Blood, torn tissue, or a pink mass sticking out? Biting or prolapse. Separate her and call the vet.
For ambiguous cases, recheck twice daily for 48 hours with a back-pressure test. If the swelling subsides on its own within 3 days, it was a quiet heat. If it persists, treat it as pathology.
For sow-stress patterns that overlap (savaging, prolapse, lameness), see the savaging sow guide and the prolapse first aid. The same poorly-stored corn often drives all of them.
Bisaya / Cebuano
Para sa mga mag-uuma
Kung naghubag ang kinatawhan sa anay nimo, una pangutan-a: mokaulag na ba (init), buntis na ba malapit nang manganak, o naa bay sakit? Ang pag-init: pula ug hubag 2 ngadto 3 ka adlaw ayha mokaylap, ug mawala sulod sa 3 ka adlaw. Ang pagmabdos: hubag sa kataposang 5 ka adlaw, init na ang teats, mga 114 ka adlaw kuwentaha gikan sa pakigsayaw.
Kung ang biik nga gilt o batan-on nga inahan naghubag ang kinatawhan, pero wala mokaulag ug dili buntis, suspetsa una ang agup-op nga mais. Kining zearalenone (gikan sa basa nga storage) maoy hinungdan. Ilisi ang sako sa mais, butangi og toxin binder. Kung baho ang agas, naa hilanat, dili mokaon, tawga ang vet, dali ug ceftiofur o oxytetracycline.
Sources
- Merck Veterinary Manual: Mycotoxin-Associated Estrogenism and Vulvovaginitis
- ThePigSite: Endometritis and Vulval Discharge Syndrome (onset after service, 50-60% farrowing rate, cull advice)
- Food & Agribusiness pig disease dossier: Vulval Discharge (90 mL endometritis volume, 14% farrowing rate)
- ThePigSite: Mycotoxicosis and the breeding pig
- NADIS: Vulva biting
- ThePigSite: Prolapse of the Vagina and Cervix
- Knox, University of Illinois: Ultrasonography in pigs
- Silvestre et al. 1986: Storage moisture and corn mycoflora
- Salvador et al. 2019: Mycotoxigenic fungi in Philippine maize (8.2% zearalenone positivity)
- AHDB: Heat Detection in Pigs
- Pork Information Gateway: Estrus Detection
