Sow Heat Detection and Breeding Timing for Pig Farmers

Pig breeding is a numbers game. A sow that produces 2.4 litters per year with 10 born alive per litter gives you 24 piglets. A sow that manages only 1.8 litters with 8 born alive gives you 14.4. That difference — 10 piglets per sow per year — is the difference between a profitable piggery and one that barely breaks even.

The foundation of those numbers is heat detection and breeding timing. Miss a heat, breed too early, or breed too late, and you lose a cycle.

The sow's cycle

Sows cycle every 18-24 days, with 21 days being the average — similar to cattle. But there are key differences:

Duration of heat: Standing heat in sows lasts 40-60 hours (2-3 days), much longer than the 12-18 hours in cattle. This gives you a wider window, but timing still matters.

Ovulation timing: Ovulation occurs about two-thirds of the way through standing heat. If heat starts on Monday morning and ends on Wednesday morning, ovulation is around Tuesday afternoon.

Best breeding time: 12-24 hours before ovulation. Since you often do not know exactly when heat started, the practical rule is: breed 12 hours after first signs of standing heat, and again 12-24 hours later.

Signs of heat in sows

Pre-heat (1-2 days before standing):

• Swollen, reddened vulva
• Restlessness, attempting to mount other sows
• Reduced appetite
• Increased vocalisation

Standing heat (the breeding window):

• Back pressure test: Press firmly on the sow's back with both hands. If she stands rigid, locks her legs, and pricks her ears forward, she is in standing heat. If she walks away, she is not ready yet.
• Sticky mucus discharge from the vulva
• Ears erect ("pricked")
• Will stand motionless if a boar is nearby (or if you apply back pressure)

The back pressure test is the most reliable indicator. Do it twice daily during the expected heat window. Morning and evening checks are sufficient for sows.

Breeding protocol

Double mating is standard. Breed twice during standing heat for maximum conception and litter size:

• First service: 12 hours after the sow first stands to back pressure
• Second service: 12-24 hours after the first

If the sow still stands to back pressure 12 hours after the second service, a third service can be done but is usually not necessary.

Natural service vs AI:

• Natural service is most common on Kenyan farms with fewer than 20 sows
• AI is available through some agrovet suppliers and allows access to superior genetics
• With AI, the timing is even more critical because boar pheromones during natural service help trigger ovulation

After breeding

Days 18-24: Watch for return to heat. If the sow shows heat signs again, she did not conceive. Record it and breed again.

Day 28-35: Pregnancy can be confirmed by ultrasound or by observing that the sow has not returned to heat through two full cycles (42 days). Most Kenyan pig farmers rely on the absence of heat signs rather than ultrasound.

Day 112-116: Expected farrowing (3 months, 3 weeks, 3 days from breeding — the pig farmer's rule of thumb). Average gestation is 114 days.

Records that matter

For each sow, track:

The wean-to-service interval

This is the pig farmer's equivalent of the dairy farmer's calving interval. After piglets are weaned (typically at 21-28 days in Kenya), the sow should come back into heat within 4-7 days.

If the wean-to-service interval is consistently over 10 days:

• Check the sow's body condition — she may have lost too much weight during lactation
• Check nutrition — increase feed in the last week of lactation to prepare for rebreeding
• Check for disease — reproductive infections delay return to heat

A short wean-to-service interval means more litters per year. At 5 days, with 114 days gestation and 28 days lactation, you get: 114 + 28 + 5 = 147 days per cycle = 2.48 litters per year. At 14 days, it drops to 2.34. Over 10 sows, that is nearly 2 extra litters per year.

Gilt management (first-time breeders)

Gilts (young females bred for the first time) need special attention:

Age at first service: 7-8 months, at a minimum of 120-130 kg body weight. Breeding too early results in small litters and increased risk of farrowing complications.

First heat detection: Expose gilts to a mature boar (fence-line contact, 15 minutes daily) starting at 5.5-6 months. Record the first observed heat but do not breed on it. Breed on the second or third heat for better litter size.

First litter expectations: First-litter gilts typically produce 1-2 fewer piglets than experienced sows. This is normal and improves with subsequent litters.

Boar management

If you keep a boar:

Do not overwork him. A mature boar can serve 1-2 sows per day. Young boars (under 12 months) should be limited to 1 sow per day with a day of rest between services.

Track his results. If conception rates drop or litter sizes decrease when a specific boar is used, his fertility may be declining. Compare his results over the last 6 months.

Feed him properly. An underfed boar produces lower-quality semen. Maintain body condition score 3-3.5.

Common breeding mistakes on Kenyan pig farms

Breeding on first observed heat signs instead of confirmed standing heat. Pre-heat restlessness is not the breeding window. Wait for the back pressure test to be positive.

Not double-mating. A single service gives 5-15% lower conception rates and smaller litters than double service. The second mating is not optional.

Keeping sows too long. A sow's productivity typically peaks at parity 3-5 (third to fifth litter). By parity 7-8, litter size and piglet vitality decline. Replace sows that have declining litter sizes over consecutive parities.

No records of farrowing performance. Without records, you cannot identify which sows are your best producers and which should be culled. Track litter size, born alive, and weaning weight for every farrowing.

Track your breeding programme at shira.farm.