Pigs Weaned per Sow per Year (PSY) Calculator — Litters per Sow per Year

How it works

Farrowing cycle = gestation + lactation + non-productive days · Litters per sow per year = 365 ÷ cycle · Pigs weaned per litter = born alive × (1 − mortality) · PSY = litters per sow per year × pigs weaned per litter

Pigs weaned per sow per year (PSY) is the headline productivity figure of a breeding herd. It multiplies how many litters a sow produces in a year — limited by the 114–116-day gestation, the lactation length and the non-productive days when she is neither pregnant nor nursing — by how many live pigs each litter weans. Cutting non-productive days through prompt re-breeding and culling, and reducing pre-weaning deaths, are the two biggest levers; leading herds now exceed 30 PSY.

Worked example

With 13 pigs born alive, 12% pre-weaning mortality, 115 days of gestation, 21 days of lactation and 12 non-productive days, the cycle is 148 days, so each sow has 365 ÷ 148 = 2.47 litters a year. Each litter weans 13 × 0.88 = 11.44 pigs, giving 28.2 pigs weaned per sow per year — rated "Good". The sow spends 29.6 non-productive days a year.

Sources: Swine eXtension — What are sow NPDs (non-productive days)? · Pork Information Gateway — Non-productive days: their significance and control

Frequently asked questions