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 |
Normal: Heat, Pregnancy, Post-Farrow
Heat swelling starts 2-3 days before the standing reflex 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 — clumping, dark spots, off-smell, 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.
Endometritis
A discharge of 30-90 mL of cloudy, foul-smelling pus at any point in the cycle, especially 5-21 days after breeding. The sow often returns to heat after a "successful" mating because conception failed. Farrowing rate in untreated cases drops to around 14% per ThePigSite.
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.
A 5-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.
For ambiguous middle cases — vulva swollen but no clear standing reflex and no pregnancy date — 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.
